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ferretbee

Idea for SWC Wicking Chamber & Orifice Experiment

14 years ago

Raybo got me thinking about the size of the wicking chamber orifice in addition to the size of the wicking chamber itself, and how they effect the amount of water wicked to the soil chamber. I'd like to get a better handle on how to manage the moisture level of the potting medium in these contraptions without so much blind trial and error. I've read that inexpensive moisture meters are pretty inaccurate, so I go to thinking about alternative ways to measure moisture--how about weight?

The experiment would take 4 identical SWCs (I'm making some smaller 3.5 gallon buckets that work well for this):

- Bucket 'A' would use a 2 inch pipe for wicking chamber with a 2" orifice.

- Bucket 'B' would have a 2 inch pipe and a 1 inch orifice.

- Bucket 'C' would have a 1 inch pipe and a 1 inch orifice.

- Bucket 'D' would have a 2 inch pipe and a .5 inch orifice.

The potting medium for all containers would be wetted in bulk, and a measured amount of water and weight of wetted potting mix added each container. Each container would be weighed to make certain they all have same total weight. The tops would be covered and the fill tube opening covered so the only opening would be the overflow hole. All 4 buckets would sit in the same room with a fairly constant room temp for 10 days to allow plenty of time for the systems to equalize. At the end, the water would be carefully pumped out of the reservoirs using a pump siphon and each bucket weighed. In theory, the best performer (the dryest potting medium) should weigh the least. If nothing else it should give a good indication if orifice size or wicking chamber volume is more important.

If the experiment works, it could be a great way to test out different potting mediums as well. Of course there are plenty of other variables like ambient temperature, warming from the sun, plant water usage at early vs. later stages, but at least this could give us a baseline for some of the other variables,

I'm open to any and all suggestions and feedback.

Comments (62)

  • 14 years ago
    last modified: 9 years ago

    ferrettbee,

    From recollection, the EarthBox does not use a wicking basket, but has two wicking "pockets" in the corners which total about 8 square inches. From my own experience with the EarthBox I own, the straight Miracle-Gro became too saturated with moisture this past season, so that is why I am attacking the "problem" by trying to find a mix combo that wicks more slowly.

    Keep up the good work with your scientific analysis!!

    Raybo

  • 14 years ago
    last modified: 9 years ago

    ferretbee - I've never tested the drainage characteristics of MG potting mix, but will definitely add a little bit of perlite to mine this year.

    Already I'm really surprised by how much water wicks through such a small hole EXACTLY

    Regarding my problems with wet potting medium, I didn't have a single split tomato last year You don't live in a humid environment - that's why.

    EG

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  • 14 years ago
    last modified: 9 years ago

    So I try to understand things in terms of inputs and outputs.

    Main inputs as I see them, contributing to moisture gain:
    -How "wicky" the mix is (hydrophilic?). Can a 1" diameter column of peat transport more water in a period of time than pine bark fines or perlite? Can it transport water further throughout the mix from the wicking hole?
    -How big the orifice is to your reservoir at the aeration bench level. Not sure how this relates to container size.

    Main outputs, contributing to moisture loss:
    -Evaporation off the top, minimized by plastic film or mulch
    -Evaporation off the sides if your container is gas permeable (ex: terracotta)
    -Plant use, highly variable as the season progresses

    Other considerations: How aerated the mix is (plant health issue, maybe directly related to the "wickability" of the mix?)
    Any others? I'm designing next years SWC, so please chime in if you've got something to share

  • 14 years ago
    last modified: 9 years ago

    OK, so I've wrapped up Wicking Test #3, but first here's a recap of Test #2:

    {{gwi:3714}}


  • 14 years ago
    last modified: 9 years ago

    Wicking Test #3

    Each cup starts filled with moist MG Potting Mix and weighs 10oz.
    Each bowl starts with 8oz of room temp water (66 deg) and weighs 8.5oz.
    Test start time 10:30am

    {{gwi:3717}}

    For this test I was looking at:
    - Small holes vs. large holes
    - Smaller total orifice surface vs, larger total orifice surface
    - Single hole vs. multiple holes
    - Results of A, B, and C vs. Wicking Test #2

    Results of Wicking Test #3: First off, this test convinced me that my Cup A results of Wicking test #2 were an anomaly. Cup A in this test showed steady water usage, where Cup A in test 2 had very slow wicking until around 23 hours, when it suddenly wicked almost 3 oz in 2 hours. My best guess is that there was a non-porous piece of something blocking, or an air pocket behind the slit. After test 2, I suggested that based on the first half hour of wicking that it was possible a 16oz wicking chamber with a 1/8 inch hole could wick up to 4.5 gallons a day. As I thought about this more, I realized that a lot of the early fast wicking we see in these tests is likely due to water table equalization between the water level of the bowl and inside the cup. The amount of volume inside the cup up to the water level at the beginning is about 3.5oz. I think a lot of the water taken in at the very beginning is just filling the bottom of the cup.

    Next, as I looked at the results of the first hour, I noticed the single hole cups were wicking more than their multi-hole counterparts. This prompted me to check the total weights of everything and I found cups B, C, and D were about a .5 oz lighter than the rest. I dont know how or where I made the mistake, but my best guess is after tweaking the water levels, I didnt lift up the water bowl and set it down (sometimes I need to do that with this scale to get an accurate reading). This discrepancy may account for most of the differences between the single and multi hole cups. I was very careful this time to wet the mix the night before and let it sit so the moisture would distribute evenly. I think I did this job too well, since there is very little difference between the cups. The only difference I can really see is that the slit cups did meter water wicking more than the holes. The 4 slit cup did wick faster than the 1 slit cup, but slower than hole cups. I was surprised at how little difference there was between the ½ inch and 4 hole cups in comparison to cups A and B. Even when the weight discrepancy is taken into consideration, the multi hole cups didnt wick more water despite have more holes and more orifice surface area. Perhaps we would have seen more dramatic differences if the potting mix started out dry. When I conducted the test suggested by engineeredgarden, I used almost dry mix and the results were dramatic, so I may try again with dry (or dryer) mix. At least I have spiffy charts to show.

  • 14 years ago
    last modified: 9 years ago

    ferretbee,

    Nice scientific approach. My "nose" is telling me that since the moisture movement up in the cup happens at a glacially slow speed, the actual "geometry" of the opening (slit or hole) may not make a difference in throttling the capillary movement of the moisture. We need some experienced Hydrology Engineers on this Forum to help explain what the data means that you are capturing.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    So if the orifice size has very little effect on how much or how little water is wicking within a certain period of time, then isn't the bottom line of the test the fact that it's all about the ingredients and percentages of ingredients in the mix rather than the orifice?

    Just wondering...

    Nice charts ferretbee!

    Donna H.

  • 14 years ago
    last modified: 9 years ago

    We need some experienced Hydrology Engineers

    That would be helpful. If it wasn't for the original cup and bowl test, (and EG's trials), I'd conclude that the size and number of openings isn't a major factor. I think it is worth noting that the higher the saturation of the mix, the less difference there seems to be between the configurations.

  • 14 years ago
    last modified: 9 years ago

    Dona,

    From my purely unscientific understanding of water movement and capillary action in a SWC environment, I would agree with you. The wicking and moisture retention properties of the Combo Mix play the predominant role.

    The exception to this would be when the "take-rate" of the plant's root system exceeds the throttling opening whereby replenishing the uptake doesn't happen fast enough. Think drinking a Slurpie through a small diameter cocktail straw.....

    Raybo

  • 14 years ago
    last modified: 9 years ago

    then isn't the bottom line of the test the fact that it's all about the ingredients and percentages of ingredients in the mix rather than the orifice?

    Very possibly. There's a couple of other things I'd like to look at as well.

    I also need to figure out why the results of 'Wicking Test #1' were so different than #2 and #3. Based on #1 results, I should have seen much more difference between Cups B and D. I can think of 2 possibilities. The first is that the mix in #1 was very dry, while the mix in #2 and #3 was moist to very moist. The other difference is that in #1, the holes were on the bottom, but in #2 and #3 I put them on the side. My thinking was to prevent any discrepancies caused from contact between the bowl and cup bottoms. A possibility is that the space between the bottom of the bowl and the bottom of the cup creates a capillary action that helps the process along.

    It should be easy enough to dry out some mix and cut a couple of holes to see what's going on here.

  • 14 years ago
    last modified: 9 years ago

    ferettbee,

    You mention that the initial potting mix was "very dry". Wicking and capillary action won't properly happen unles the potting mix is wetted first to initiate the "conveyor belt". The EarthBox folks make this very clear in their instructions. You need to start the system with moist potting mix to begin with.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    "The exception to this would be when the "take-rate" of the plant's root system exceeds the throttling opening whereby replenishing the uptake doesn't happen fast enough. Think drinking a Slurpie through a small diameter cocktail straw..... "

    Oh absolutely! That was clearly demonstrated last season between the different varieties of veggies I planted. My bush beans (which did fabulously!) were absolutely in love with the relatively equal wetness of the mix although they were in 3.5 gal containers while the tomatoes were really saturated toward the bottom and then dry closer to the top in the 5 gal containers and did miserably (there was some human error here also.)

    My initial thoughts, which I posted in this forum under "My First Growing Season With SWC's - Notes And Comments From A Complete Beginner" noted that based on how poorly my tomatoes did, the culprit was likely the container size. In retrospect, my reasoning was obviously flawed as many people have successfully grown tomatoes in 5 gal buckets. And why shouldn't they? The EB's dimensions are 29L x 14W x 11H and hold TWO plants. A 5 gal bucket's dimensions are 12W x 14H and basically hold ONE plant. Although the soil depth for the 5 gal bucket is about 1 1/2 times deeper (which could be lessened if necessary) and the width is 2" less, (EB's dims divided by two) it now seems foolish to believe that those two factors would by the ONLY culprits here.

    Which brings me back to the growing mix.

    As I stated before, my mix had 'issues' with compacting. Not so much of an issue with smaller root systems in smaller containers, but a HUGE issue with the tomatoes with a more complex root systems and growing in larger containers.

    So I guess if the mix is has the correct percentage of ingredients, is blended properly and is properly wet, then the wicking chamber (although primary to the function of the SWC) takes on a secondary role once the hydration equilibrium has been found. From that point, uptake of hydration and nutrition should be a 'done deal, based solely on the mix. Hmmmmmmmm...

    These experiments are absolutely fascinating! And so helpful to us newbie SWC growers. Thanks Ferretbee, your results have really given me a lot more to consider.

    And Raybo...I'll be following your "mix" thread with increased scrutiny... <:->

    Donna H.

  • 14 years ago
    last modified: 9 years ago

    Donna,

    My trials for 2010 will focus on both the 3:2:1 and 3:3:2 ratios of Potting Mix, Bark Fines, and Perlite. I will do some 'Tainers using these ratios with Miracle-Gro as well as Sta-Green using the same plant pairs, to observe which produces healthier, more productive tomatoes.

    For my Pepper plants, I will focus on the 3:3:2 ratio, but again, I will do some with Miracle-Gro and some with Sta-Green Potting Mixes.

    So my 30+ combination trials of the Fall Season should collapse down to about 6 Mix Combos for 2010.

    Next, I am going to experiment with traditional Fertilizers like the "Old" Tomato-tone, as compared with ALL SEASONS 19-6-12 CRF (that I pay $0.66 per pound in 50 pound bags) to see if there is a significant growth and yield difference between the two.

    A never ending "experiment", but it keeps my brain working......and off of Dear Wife's "radar-screen" when I disappear outside.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    Hi Ray, I did consider the Earthbox instructions about pre-wetting the potting medium, which is why I wet the mix for tests 2 and 3 to a similar level of moisture recommended when setting up a SWC. I don't think it's necessary for these little tests since I'm looking at the wicking at the bottom level. If you dip the corner of a dry paper towel in water, the water will wick up a couple of inches. What I saw with EG's simple cup and bowl demo was that the big hole wicked a lot faster than the little hole. The difference was visible to the naked eye in just 5 minutes. So far, I have been unable to replicate that simple result with wetted potting mix, and I notice that more saturated the mix becomes, the less difference there is between the cups. So I'm thinking I may need fairly dry mix in order to see and quantify any difference. I don't have any dry mix so right now I have a pan filled with potting mix in the oven....

    I was re-reading Al's water movement post and thinking about your 'straw' analogy and how a small hole might meter water better than a large hole. I don't know if it means anything, but I checked how long it took for 8oz to empty out of a 1/8 inch hole. It was really fast (under 2 minutes)--far faster than a plant uses water. Now obviously, gravity and capillary action are different forces, but I can't help but wonder why, in a low pressure low volume situation it would throttle one way, but not so much the other...

    Donna, that was a great post. I looked it up again and noticed that most of the veggies that did well had lower moisture readings. I can't help but wonder if the plants were healthy because of less moisture, or there was less moisture because they were healthy. I also noticed you mentioned using 2 cool whip tubs for some containers. Were those a little larger than the other wicking containers, and if so was there any correlation between wetness and the larger wicking baskets?

  • 14 years ago
    last modified: 9 years ago

    With this test I was trying to replicate EG's small hole vs big hole demo, and also check for differences between side holes and bottom holes. Based on tests 2 and 3, it seems the more saturated the potting mix gets, the less important the opening size and configuration is, so for this test I used MG potting mix right from the bag that was slightly moist and non cohesive when squeezed. It still wasn't as dry as I would have liked. This time, I also started with the cups full and weighing 12oz, and a little more water in the bowls, starting out at 10.5oz. I checked the total weights at the beginning this time to make certain everything started on a level playing field. Here's today's spiffy chart:

    Conclusion: Again, there's no indication that the small holes slow down wicking. There also doesn't seem to be a big difference between side holes and bottom holes for most of the test. The bottom holes are a bit slower at the beginning, but I think a lot of the early water uptake in the first few minutes is just the water leveling out. I can't explain yet why this test doesn't correlate with the EG's demo, or his trials. I am pleased with the similarities between the side and bottom holes since I have an idea that requires a single side hole in the wicking chamber.

  • 14 years ago
    last modified: 9 years ago

    Ferretbee,

    I want to be very much supportive of your experiments, so please take my comment in a constructive mindset. Above (2 posts) you use the analogy of a paper towel wicking up water, and that dry potting mix exhibits the same properties. I do not agree with this at all. Take a full cup of dry potting mix, then pour a stream of water on the top of the mix. 99% of the water will simply roll of the surface and dribble down the outside of the cup.

    Dry potting mix is "Hydro-phobic" - - it will not wick up water in its dry state. You really need to make a concerted effort to immerse the potting mix and stir it about in water for it to become saturated. I had this experience this evening where I wanted to start 18 Pepper seeds in dry potting mix. I had to take over an hour of constant watering and re-watering to get the potting mix to fully saturate in the cups.

    I have also seen in EarthTainers where I didn't fully saturate the potting mix upon filling, that there were permanent pockets of potting mix that never became wet throughout the season. Analogous to mixing Sackrete concrete mix, you water the wheelbarrow with a lot of water, thinking you are flooding the mix, then start to turn over the concrete mix only to find the layer an inch below is totally dry.

    I advise folks who build EarthTainers to really soak the potting mix when installing initially in 3 inch layers, until water comes out of the overflow holes; then let the 'Tainer "stabilize" a week to equalize moisture before planting the vegetables.

    Just my personal experience from several years of observation. Why dry potting mix is "Hydro-phobic" is beyond my technical ability to explain.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    Hi Raybo,

    I welcome all comments and suggestions, that's the best way to figure things out. I understand what you mean about dry mix being hydrophobic, and I agree that wetted mix is important in starting a SWC. It's especially critical in the soil chamber since the higher you get from the reservoir the harder it is for capillary action to overcome gravity. In this case, I'm not worried about mix begin too dry for a little cup test since the mix is so close to the water. I'm not planning on using 100% bone dry mix, but I want the mix to take longer to get saturated so there's more time between the initial water rush and high saturation to see differences in performance. The worst case scenario here is that I run a test and have a couple of cups that won't wick. I promise that no plants will be harmed during the filming.

    EG may be right, and I may need to upscale to full size SWCs to properly evaluate anything. If that's the case, at least these little tests have provided some useful info for a methodology of evaluating larger containers. I think a 3.5 gallon in a 5 gallon setup will be best for this. I made some mini-SWCs out of 5 cup containers, but I think they're way too small to provide much useful info.

    One thing the potting mix casserole has revealed is that my MG Potting Mix is made up of mostly fine dust. There's no visible shreds of peat, it's all small particles with occasional chunks of wood. No wonder my containers were waterlogged.
    After I use the MG I've dried in the oven, I'm not going to use any more for testing purposes. I was able to pry my frozen bag of Sta-Green from the ground and will thaw it out for future tests.

    I'm hoping I can find a good supply for pine bark fines cheap. It seems to be the key ingredient in many successful SWC mixes.

  • 14 years ago
    last modified: 9 years ago

    Ferettbee,

    I would suggest you commence your experiments with slightly moistened Potting Mix - - not bone dry. I believe this will give you a "kick-start" to your wicking evaluations.

    I get my Bark Fines at Home Depot. About $2.00 per cubic foot, so it is much cheaper than the potting mix. Here is a photo of what to look for:

    {{gwi:681}}

    I try to expose these to sun and rain water to get them to "age" a bit before putting them into their 'Tainers.

    Happy Hunting!!

    Raybo

  • 14 years ago
    last modified: 9 years ago

    "Donna, that was a great post. I looked it up again and noticed that most of the veggies that did well had lower moisture readings. I can't help but wonder if the plants were healthy because of less moisture, or there was less moisture because they were healthy. I also noticed you mentioned using 2 cool whip tubs for some containers. Were those a little larger than the other wicking containers, and if so was there any correlation between wetness and the larger wicking baskets?"

    Ferretbee: Thank you for your kind words. And I do think you raise an intriguing point regarding the moisture levels, but I found that most of the pots were TOO moist for my liking. On my meter, the ideal level of moisture would have been 3.5 - 7.5. In reviewing my results, they were as follows:
    Strawberries 10+ WAY too high!
    Green Beans: 8 Too high
    Eggplant: 5 PERFECT
    Hot Peppers: 6 PERFECT
    Green Peppers: 8 Too high
    Zucchini: 5 PERFECT
    Watermelon: 5 PERFECT
    Cantaloupe: 7 PERFECT
    Tomatoes: O for the first 1" and increasing for the full length of the meter tines at which point it was 10.

    I used 24 oz. cottage cheese containers for all the 5-gal double SWC's and a 6 oz. yogurt container for the 3-gal double SWC's. It's interesting that using the 6 oz. yogurt cups that I thought were appropriately sized to the smaller 3-gal containers, actually wicked up the most water. BUT...in that case, due to a relatively small root system, the uptake probably didn't keep up with the amount of saturation.

    In looking at the other veggies that had high moisture levels, they're root systems were also relatively small so Raybo's point is also valid:
    "The exception to this would be when the "take-rate" of the plant's root system exceeds the throttling opening whereby replenishing the uptake doesn't happen fast enough."
    I would only add that the reverse is also true (as was demonstrated in my SWC's last year): When the "take-rate" of the plant's root systems is LESS than the throttling opening when used in combination with a dense soil mix, replenishing the uptake actually happens FASTER than the plant requires and thus, its roots remain saturated.

    So while the orifice may be small, and the wicking chamber may also be small, the problems really occur when they're used in combination with a dense mixture by a plant whose root system can't possibly handle the extra water.

    Using a formula from a SWC book, I made the growing medium from raw ingredients. I'm not fond of MG potting mix...too many sticks and fungus gnats, so I like the fact that I can adjust the percentages to accommodate each plants needs. I'm beginning to think that I should use one mix for most of the plants in the 5 gal SWC's and a completely separate one for JUST the tomatoes since that is where I seem to have the most trouble with wicking and high moisture variables.

    As far as the wicking chamber and orifice sizes, based on your results, I don't see any reason to change those two factors for my SWC's.

    Donna H.

  • 14 years ago
    last modified: 9 years ago

    Donna,

    After experimenting for many Seasons now in SWC applications, I have personally become convinced that the Combo Mix is 90% of the equation, and the wicking orifice opening is perhaps 10%. Also to your point on varieties, I find that my sweetcorn likes large amounts of moisture, but tomatoes are more productive in a mid-range moisture environment. More trials to continue this Season...

    Raybo

  • 14 years ago
    last modified: 9 years ago

    Thanks for the extra info Donna, I find all of it interesting and helpful. According to your post, you used slits in your wicking chambers instead of holes. In my tests, slits showed some promise of restricting water intake, but only until a certain saturation point. That 'could' explain why your Zucchini, Watermelon, and Cantaloupe containers weren't too wet. They're all heavy drinkers, so it's possible they exceeded your wicking chambers ability to saturate the soil chamber. Were you able to get moisture readings when the plants were small?

    I tend to agree that a proper mix is most likely the main factor for a good SWC setup. What I'm attempting to do is narrow down how some of the other variables might effect the moisture level of the mix in the soil chamber.

    I have concluded that making a bunch of holes in my wicking chambers is very likely not necessary. If this is correct, then it also means that there's no advantage to using a pond basket over a food container with a couple of small holes. Raybo might want to test this out since it would reduce the cost of building an Earthtainer, and also make it a little easier to source the wicking chamber. This is untested, so I'm not encouraging anyone to alter his design until it's been verified by Raybo.

    Test after test, it seems like the 1/8 inch hole cups wick slightly better (and definitely not worse) that a much larger 1/2 inc hole. I don't know if I'm quite ready yet to build an 18 gallon SWC for an Indeterminate Tomato with just a single 1/8 inch hole in the wicking chamber, but I think there's a good possibility that it would delivery enough water to such a thirsty plant. I'm still unconvinced that it would keep the soil chamber from getting too wet if the mix is too hydrophilic. I don't doubt EG's trials, but I may have an alternate explanation as to why his 4 and 5 gallon setups with a the 1/8 inch wicking orifice are working so well.

    I have some more results I'll post later.

  • 14 years ago
    last modified: 9 years ago

    My reason for this test is that I've been unable to reconcile the results I saw with EG's cup and bowl test and Wicking Tests 2, 3 and 4. When I tried the initial cup and bowl test, I just scooped some potting mix from the top of the bag and it was pretty dry, so I thought I'd try a test with dry mix to attempt to recreate the results. To get some dry mix for the test I baked some MG in the oven for day.

    My main concern was small hole vs. large hole in dry potting mix. I was hoping large hole would wick faster so I could reconcile Test 1 with 2, 3, and 4. Raybo was concerned about using dry mix, so I added a 3rd cup to the test with moist potting mix for comparison.

    Again, small hole did a bit better than the larger hole. The dry cups caught up with the most mix in about 20 minutes, and then wicked more water than the moist. At about 3 hours, the dry mix cups were moist about half way. I'll leave them overnight to see how far up capillary action will carry up the dry mix.

    This still didn't answer why Test #1 was different.

  • 14 years ago
    last modified: 9 years ago

    I want to figure out why it seems the large hole wicked a lot faster than the small hole the first time I tried this. What I saw wasn't just random, the larger hole definitely wicked water to the top faster, but in all my subsequent tests, that has not been the case, so for wicking test #6, I decided to recreate that 1st test as closely as possible, but under the more controlled conditions and record keeping as the other tests. When EG suggested the test, I didn't have any cups around, so I used a couple of dixie cup type bowls set in food containers. The main differences between this and the plastic cups in the other tests is that the potting mix container is more shallow, and the bottoms of both the dixie bowls and food containers are smooth, while the Solo plastic cups are indentated on the bottom with lettering molded in. So for this test, I used 2 dixie cup bowls set in 5 cup Rubbermaid food containers. Since Test #5 trashed the dry mix theory, I used slightly moist mix.

    I could see early on that the larger hole was wicking more water than the small hole. I'd wondered if the smooth surfaces of the cup and container had anything to do with capillary action moving water to these bottom holes, so around 12 minutes I looked at them from the bottom (the food containers are clear). I didn't see anything much under Bowl A, but under Bowl B, I could see small particles of potting mix moving quickly towards the hole. What I believe happened is that the larger hole allowed some mix to spill out, and this created a small gap of space between the bottom of the bowl and the bottom of the food container. I could slightly lift a corner of the bowl and watch the flow of particles speed up. Lift up too much and flow nearly stopped. When I checked Bowl A again, there were no particles trapped or moving under the bowl.

    My theory here is that capillary action between the smooth bottom surfaces moves water into the orifices faster than a hole on the side. I'll need to find some smooth bottom cups to test for certain. I don't know if the larger hole wicked faster in this case due to the size of the hole, or from the space created by mix that fell out of the larger hole.

    I had already somewhat discarded the idea of side hole vs. bottom hole after Test #4. But watching these wick from the bottom got me thinking about the slightly slower wicking of the bottom holes in the early part of that test. If the bottom of a smooth cup could help create more wicking through capillary, and the gap is critical, then perhaps the rim of a cup against the bottom could also restrict, or even stop water from wicking into a bottom hole...

  • 14 years ago
    last modified: 9 years ago

    Ferretbee: You're welcome! I love the exchange of information that goes on in this forum.

    Yes...the 'heavy drinker' scenario is probably what happened with the larger plants. Unfortunately, I did NOT take moisture readings when the plants were small. I was just so darned thrilled that they were healthy, I didn't bother. This year, I will keep much more detailed records...to be sure!

    I too am keenly aware of the cost and wanted to keep it as low as possible since this was my first attempt at SWC's. The cottage cheese and yogurt containers worked quite well and yes...I did slits since the container material did not lend itself to drilling holes.

    As far as the 3.5 and 5 gal double SWC's are concerned, I do NOT believe that the pond basket is necessary. But with a larger container design such as Raybo's 31 gal SWC, it just might be, especially for tomatoes. By the time I get around to building those however, Raybo will probably have improved on the design yet again!!! ;-)

    Donna H.

  • 14 years ago
    last modified: 9 years ago

    Ferretbee,

    You certainly don't need to use a pond basket as the wicking basket - - any sturdy container with the approximate dimensions of 4 to 5 inches in diameter, with a 4 inch depth will work just fine. The Pint containers you get in the Deli Department at a food store will also work great.

    I still have a concern about attempting to "throttle" the moisture intake with small holes in the wicking unit. My experience is that the intake required in gallons per day for May, will be significantly exceeded when August rolls around, as the plants uptake rate will be 3-times the daily amount at that time.

    If you could devise a valve that could be dynamically adjusted as the plant's uptake increased, this would be ideal. How to do that inside a SWC is another challenge....

    Raybo

  • 14 years ago
    last modified: 9 years ago

    Another thing that bothered me about the results of Tests 2,3,4,5 is that EG (engineeredgarden) has been testing DIY 4 and 5 gallon bucket SWCs with smaller and smaller wicking chamber orifices. I believe his basic design for a 4 gallon SWC are 2 kitty litter buckets with a yogurt (or similar) container as a wicking basket, and is now using just one 1/8 inch hole. He's been using MG mix and getting good mid level moisture readings. The plants he's using for trials are not huge drinkers. My little tests indicate that a small hole wicks just as much as a big one (and maybe a bit more), so what's going on here? Could my tests be wrong? Do I need to go 'full scale' to go further?

    So going back to Test #4, where the bottom holes wicked slower at first, and then onto #6 where I noticed the bottoms of the bowls against the bottom of the container, I began to wonder if the bottom rim of one of these cups could actually act like a valve.

    I took an empty plastic cup with a 1/8 inch hole in the bottom and placed it in an empty glass bowl with a smooth, flat bottom. I pressed lightly on the rim of the cup while I poured about 8 oz of water into the cup. A little water came out the bottom, then it stopped. I filled the cup all the way up with water and no more moved into the bowl. I then lifted the cup up a bit to allow some water into the bowl, then sucked the water out of the glass with straw until the cup was empty. No water from the bowl moved into the cup. That's working like a valve.

    Now, in EG's containers, it could be that the bottom rim of the wicking chamber pressing against the hard bottom of the bucket is acting in a similar way as the slits restrict some water flow, or perhaps it's more extreme and the more water that wicks up into the wicking and/or soil chamber, the more weight is pressed on the rim of the wicking chamber, and the less water gets in. In many 'bucket in bucket' SWC designs, the wicking chamber just sits in hole in the bottom of the top bucket and is not physically connected to either bucket, so it is possible that it could move a tiny fraction as the weight of the mix changes. It's a long shot that it actually works that way, but if it did, it would be self regulating and very cool...

    EG's been working on full trials with complete SWCs and growing plants. I have some cups of dirt, so take my ideas with a grain of salt.

  • 14 years ago
    last modified: 9 years ago

    Raybo,

    How many gallons a day can your ET's go through at peak times?

    If you could devise a valve that could be dynamically adjusted>

    I'm working on it. I have all the parts, and cost under $8 at Lowes. Based on my cup tests, I'm skeptical that it will work well to make adjustments, but it should work great as an on/off for the water reservoir.

  • 14 years ago
    last modified: 9 years ago

    So, all wacky cup valve theories aside, here's a pretty straight forward test that seems to have some conclusive results, 32oz cup vs. 18oz cup. I also had a 1-1/4 inch pipe to try out a small volume, but it didn't wick. Possibly, I packed the mix in too tightly:

    This seems pretty conclusive, even after accounting for the greater water displacement and water leveling out, the big cup wicked noticeably more water than the small cup. At 4 hours I added 4oz of water to each bowl since J was almost empty. I'd like to run again using a wider bowl for J so the water level would be similar to B at the beginning. I don't know if more wicking from a larger wick chamber would equal more water in the soil chamber, but it's a possibility that I'd like to examine further.

  • 14 years ago
    last modified: 9 years ago

    I've continued my wicking tests and believe I've learned a lot. Just the process of running the tests and trying to analyze the results has been helpful. After several tests I've concluded that the early results are nothing more than the water level evening out, so I've changed my tests a bit. I'm now starting with some highly saturated potting mix in the cups filled up to about the water line, and letting the water level even out before proceeding. This should give me a better idea of the actual differences in wicking. This makes it more difficult to start with exactly the same amounts of water and potting mix, so I'm weighing the water reservoir at the beginning of the test and will post results as water removed from the reservoir. Some of this is evaporation, but previous tests show this is less than .1oz per hour.

    On the other end of the spectrum, so far all tests have shown that the more saturated the mix becomes, the less important and physical differences in the mix matter. Over time, most of the setups have wicked the same amount of water.

    I'll soon be posting some results which will (hopefully) make more sense than some of the previous ones.

  • 14 years ago
    last modified: 9 years ago

    This was a simple A-B test where I used landscape fabric in the bottom of the cups to keep mix out of the water. One cup had a 1/2 inch hole and acted normally, but the other cup had a 1/8 inch hole and kept floating. I weighed it down but it took nearly 20 minutes for it stop floating. Due to this unexpected result, I'm throwing out the results, but will add a landscape fabric test to Wicking Test #10.

  • 14 years ago
    last modified: 9 years ago

    This is a follow up to Test #7, which seemed to indicate a larger wicking chamber would move water faster than a smaller one. I let cups B and J run for a couple of days and added 4oz of water a couple of times. The larger cup slowed down when the water level got low, and the water uptake leveled off once both cups were very saturated. That seems logical, but I wasn't totally satisfied with the test. I will be repeating this test as part of #10, and hopefully reducing some of the variables of #7.

    The purpose of Test #9 is to take a further look at mix volume and water depth in the wicking chamber and how (or if) it effects water uptake. Specifically, does the amount of mix in the wicking chamber below the water line effect water uptake? Designing this was a little trickier than previous test, but I think I did a decent job.

    {{gwi:3721}}

    I made 2 wicking chambers out of small water bottles, one short, and one tall. I marked them an equal distance from their respective tops (this would be the water line). I filled each container up to the water line with full saturated mix, and then each reservoir with water up to the line. After a few minutes, I filled the cups to the top with slightly most MG mix and started the test:

    Only very slight difference (I'd say within the margin of error), but nothing major and not what you would expect if the larger amount of submerged mix had a 'booster' effect on water uptake.

    If a larger wicking chamber moves more water, but the volume of mix below the water line doesn't matter, then (by my reasoning) the surface area of mix in contact with the water line is a key component in how much water the wicking chamber can move.

    I have an idea for a demonstration with a sponge that might illustrate this better.

  • 14 years ago
    last modified: 9 years ago

    This test gets a bit complicated because I'm running several different experiments at the same time. It includes some repeats of previous tests in addition to some brand new ones. I switched to Sta-Green Potting Mix for this test, and also filled the cups to the water line with saturated mix and let the water level even out before starting. For the odd sized cups (J and L), I started with same water depth as the rest:

    {{gwi:3723}}

    Here's the setup for the large wicking chamber J:
    {{gwi:3724}}

    Here's some results, I'll try to explain each cup and what we're trying to compare:

  • 14 years ago
    last modified: 9 years ago

    Cup B is the same cup I've used in many of the earlier tests. It's purpose here is primarily as a control to compare against some of the other cups. It's an 18oz plastic cup with a 1/8 inch square hole on the bottom of the side.

    Cup H is the same as B, except the hole is on the bottom and I'm keeping the top covered to reduce evaporation. It's purpose is primarily as a control for Cup Q, but also as a repeat of 'side vs. bottom hole'. The results of B vs H are pretty interesting. Now that we've removed the initial water leveling off, we see it wicks just a well as the side hole, possibly a bit better. This is consistent with Test #4. I still think there might be some funky stuff happening with bottom holes that needs further investigation.

  • 14 years ago
    last modified: 9 years ago

    This is a repeat of #7. This time, the water reservoirs were started at the same depth, rather than the same volume. Over time, just the additional mix in J will allow it to wick more, but I'm looking to compare the results up to saturation of L.

    Cup J: 32 oz cup with a 1/8 inch hole in the bottom side. The diameter at the bottom is 3.75 inches.

    Cup L: This is the tall cup made from a water bottle in #9. It's 12oz and has the same hole, and is 2.5 inches in diameter.

    Looks like J is the winner (or loser if your SWC is too wet). The bigger wicking chamber wicks water faster than the smaller one. It's also interesting to note that L wicks at a similar rate to control B. Despite the fact that L has less volume, they have about the same diameter at the water line. This lends further credibility to my theory that the surface area at the water line has an effect on water uptake. L hits it's saturation point sooner since it has less volume.

  • 14 years ago
    last modified: 9 years ago

    Ive suspected that landscape fabric could slow down wicking and draining, so I added it to this test.

    Cup M: Identical to the control (B). I added a circle of 15 year landscape fabric inside the cup at the water line. I soaked the fabric for several minutes before the test.

    For most of the test, M wicked half the water of B. It's starting to catch up as B gets more saturated. This seems pretty conclusive to me. While landscape fabric is permeable to water and air, it does slow it down. Hold a piece to your mouth and try breathing through it to demonstrate.

    This could have a couple of implications in SWCs. In Raybo's Earthtainer instructions, there is a layer of fabric between the wicking and soil chambers. If it wasn't for this layer, the ETs might be much wetter. It's also possible that fabric on the soil bench impedes draining, making it harder to dry out an over saturated soil chamber, and/or restricting air to the roots.

  • 14 years ago
    last modified: 9 years ago

    In earlier tests, the 1/8 inch holes wicked just as fast as the 1/4 inch and 1/2 inch holes (possibly a bit more). For this part, I wanted to try even smaller holes to see if there was a difference.

    Cup N: Identical to B, but with a pinhole made with a large safety pin in the bottom of the side.

    Cup O: Identical to B, but with a 1/16 inch square hole on the bottom of the side.

    It looks like we finally have a failure (the good kind). Cup N seems to have stopped wicking. This is the first cup to stop wicking before saturation. It might be interesting to see if multiple pinholes would yield similar results.

    O wicks a bit slower than the control (B), but not that much, especially when you consider it has 75% less surface area of the hole in B.

  • 14 years ago
    last modified: 9 years ago

    One of the early solutions proposed to reduce wetness of the Earthtainers was to make the opening between the wicking chamber and the soil chamber smaller. I wanted to look at that closer, so for this test, I kind of 'simulated' a smaller opening inside of the cup.

    Cup P: Identical to the control (B), but has a circle of plastic with a 1/2 inch square hole in the middle buried about 2/3rds of the way up.

    I don't fully understand these results. I expected if anything differed from the control, it would happen later on in the test, but this cup lagged behind a bit from the beginning.

    This could be an anomaly, so I won't draw any conclusions until I see this result repeated.

  • 14 years ago
    last modified: 9 years ago

    For this test, I wanted to try out my theory that the bottom rim of a wicking chamber cup with the hole in the bottom could act like a shutoff valve with weight added.

    Cup Q: Identical to Cup H. For the water reservoir, I used a glass bowl since the plastic bowls had some embossing that might hinder a good seal. At beginning of test I placed a bowl and a container of water weighing a total of 2lb 10oz on top of the cup rim. After the first hour I weighed Q just once per hour so the 'seal' would be disturbed less.

    I can't say it sealed it 100%, but it did slow down wicking by a wide margin. In real life, I don't think it's a major concern, but it could happen under the right conditions.

  • 14 years ago
    last modified: 9 years ago

    Ferretbee,

    The original wicking orifice opening in the first EarthTainer was a 8.5" by 8.5" opening (75 square inches). At that time I was absolutely convinced that even with this size opening, getting the moisture to wick up 10" to the top surface was going to be problematic. Little did I understand Capillary action, and how this size opening actually caused the moisture to WOOSH up into the potting mix.

    I gradually modified the orifice opening down to a 2" by 8" opening (see the original EarthTainer Construction Video) and it turns out the potting mix still got too saturated. That is when I shifted focus to the mix composition as the main determinant of moisture saturation.

    Keep in mind that the commercial EarthBox uses two wicking "chambers" that combined, total only 8 square inches, and mine with straight Miracle-Gro potting mix gets far too saturated. When emptying it, I get the distinct aroma of rotten eggs (SO2) so that is telling me something is amiss.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    Hi Raybo,

    As I recall, you made 3 changes to the ET Watermeiser:
    - Smaller wicking basket
    - Lower Water Line (and larger soil chamber)
    - Smaller wick to soil opening.

    I think all of those could have contributed to improved balance, but it'd be great to know how much each aspect of the changes contributed.

    I beleive the MG Mix (AKA Peat soup) was a major contributor to my waterlogged SWCs, but I also beleive there was also a mechanical component since the 5 gallon SWCs were wetter than the 18 gallon. There must be something to it, since soil bench sagging can lead to super saturation.

    I took some measurements of an Earthbox last night at a local garden center. The wicking chambers were just about 3 inches cubed, so the surface area would be 18 square inches. I was struck by how short the EB and Grow Box are. The EB is just about 10 inches deep for the reservoir and soil chamber. Depth is a major factor in wicking and draining, so I think it's probably a lot easier to balance a 10 inch deep container than a 20 inch. I found out the Earthboxes are manufactured just a couple of miles from here.

    I'm hoping my stupid experiments can guide me when making changes so I'm not so darned clueless.

    I've read that a tomato plant can drink up to a gallon a day. That sounds low to me, so if anyone has any thoughts please chime in.

  • 14 years ago
    last modified: 9 years ago

    Ferettbee,

    My original EarthTainer I used a 9" by 9" by 6" wicking basket. By reducing the orifice, I was able to go to a lower 4" high, 5" diameter basket. This increased the potting mix volume potential in the EarthTainer II by 20%, which is a good thing for root development.

    The surface area of the EarthBox wicking is 2" by 2" in the two back corners, which adds up to 8 square inches - not 18 square inches. the wicking volume (combined) is 2x2x2 for each chamber, adding up to a total of 16 cubic inches.

    Regarding daily plant uptake, I do believe a tomato plant in the prime of Summer can intake 1+ gallons per day. I would love to incorporate a mini-flowmeter in the AWS someday to actually chart how the plant intake rates varies per day throughout the Season.

    Raybo

  • 14 years ago
    last modified: 9 years ago

    I converted the data to a chart to make it easier to see the results:

  • 14 years ago
    last modified: 9 years ago

    This is basically a repeat of some earlier tests:

  • 14 years ago
    last modified: 9 years ago

    In test #3, I didn't see the expected results of multiple holes vs. single hole. This time 'B' (single hole) wicked slower than 'F' (4 holes), as you would expect. In #3, I may have made slight weighing errors at the beginning, and I think it also helps to start with the mix saturated up to the water line. It's also interesting that 'N' (4 pinholes) wicked at a very similar rate to 'B', and that 'B', 'F', and 'N' all wind wicking almost the same amount of water.

  • 14 years ago
    last modified: 9 years ago

    This was supposed to compare the difference with a piece of landscape fabric in the mix (repeat of #10). Unfortunately I forgot to put the fabric in when setting up, so had to go back in about 10 minutes later to fix the error. I have to throw these results out since the process of messing with the mix may have altered the result.

  • 14 years ago
    last modified: 9 years ago

    This is a repeat and expansion of the orifice test (cup P) in #10. this time, Cup P had the plastic disc with a 1/2 inch hole in the middle buried about 1/3 from the top. Cup R had a disc with a 1 inch hole buried about 2/3 from the top. This time, 'P' was similar to the control 'B', but 'R' wicked slower and less volume. Furthermore, 'P' and 'R' never got fully saturated at the top. The mix above the discs was dryer than the other cups.

  • 14 years ago
    last modified: 9 years ago

    For this test, I wanted to repeat aspects of #4,5, and 6. I wanted to use cups with flat bottoms, but couldn't find any so I used styrofoam cups and trimmed of the bottom lip and sanded flat. I also switched to Rubbermaid containers for the water reservoirs since the plastic bowls had lettered embossed on the bottom.

    {{gwi:3726}}

  • 14 years ago
    last modified: 9 years ago

    I was more careful this time to make certain they started with the same weight of saturated mix to the water line, and again with moist mix above that. I think there are probably differences in the ratio of water to mix at the start, but the only way around that is to start with completely dry mix. This may account for some of the variations in results I've seen with some of the tests.

  • 14 years ago
    last modified: 9 years ago

    The larger bottom hole 'C', and multiple bottom hole cup 'D' wicked at similar rates and slightly faster than the control 'A' and small bottom hole cup 'B', but all converged after a few hours. After that, I can only attribute the slowdown of 'D' to a more saturated mix at the beginning of the test.

  • 14 years ago
    last modified: 9 years ago

    I've been reading a lot about Al's mixes, and also got some good advice for overwintering a bell pepper by transplanting it to a fast draining mix. We all know that water molecules slow down when the get cold (forming a solid below 32 degrees) and speed up when they get hot (forming a gas at boiling point). I wondered how great of an impact less drastic temps have on wicking, so Cup 'E' was identical to 'A' but went into the fridge. The water temp dropped to 36 degrees at 1 hour, then to 32 at 3 hours. I removed 'E' from the fridge at 24 hours and wicking slowly resumed. I should have added an evaporation control in the fridge, but it's still pretty clear that cold slowed wicking compared to the room temp (65 degree) control.