Pretty cool design. One thing that struck me about your experiment was this "So what I am experimenting with today is throttling back the capillary action by reducing the orifice opening with two trial size openings (45 sq. inches, and an even more constrained 26 sq. inches). My goal is to find the right opening to yield a "moist" result on the meter throughout the container."

I don't know that reducing the size of the wicking chamber is going to be as significant as you are hoping. While it may slow the rate at which water enters the mix, it isn't going to have any impact on how much water the mix can hold.

During the prime growing season with high temps (evaporation) and large plants it might work out, but unless something is removing water from the mix at a pretty good rate the mix will still get just as wet as it did with a larger reservoir opening. It will just take a little longer to fully saturate.

You might want to switch to a less water spongy mix if what you are currently using is getting too wet.

Thanks for the tip on the potting mix. I am using Miracle Grow with Moisture Control, as I thought this product would be ideal for Earthbox type applications. While this is only March and my meter is reading "wet" throughout the 'Tainer, I am hoping by summertime with the 2 tomatoes ramping up their drinking habit, that the moisture content will stabilize into the moist range.

My common sense it saying that the original 76sq. inch wicking orifice is simply too large, and my hope that an effective basket surface area around 40" will be about right. Trial and error....

Raybo

Nothing wrong with some trial and error. You are correct that tomatos drink a lot of water and mix that is too wet right now might be just about right in the summer for grown plants setting fruit.

The moisture meter you are using is essentially a worthless piece of junk ;-) It doesn't measure moisture at all, but electrical conductivity. Here is a link explaining how they work. It's a pdf file so you need Adobe Acrobat reader. In particular look at page 4.

Long story short things that throw the reading off are high organic matter content, fertilizer (salts), clay and anything else that changes the electrical conductivity of the mix.

As a rule of thumb any type of probe instrument for gardening is junk. None of them are reliable. The only ones that have a chance of being accurate come with replaceable probes, special storing procedures to keep the probes functional and without exception a means of calibrating them before use. All others are a complete waste of money.

As far as opening size for the wicking area, just going from visual memory the commercial earth boxes have 2 wicking chambers that are roughly 2"x2" for a total of 8 square inches on the surface, but they are a few inches deep. Gardener Supply boxes (the kind sold for tomatos) have slots running the width of the box that are less than an inch wide. I believe there are 6 or 8 of them (I forget). These are shallow.

The Gardener Supply boxes are better at wicking the water all the way to the surface, but the difference isn't significant. The moral is the water is going to wick no matter what and the mix itself will have more of an impact than the size of the wicking chamber(s)in terms of how wet it gets although the size does influence how quickly the mix wets.

Happy experimenting. If all else fails you can always remove the fert strip and top water

Hey justaguy2,

Thanks for the information on the (in)accuracy of these inexpensive moisture meters. I was just hoping it would be a "relative" indicator of moisture - - not an absolute reading. I have a 3' high Cherokee Chocolate that I transplanted from house windowbox, to outside on Feb 11, and so far, it is doing quite well, even in the "wet" reading on the meter.

Just to be on the conservative side, on the next 13 I am currently building, I am shrinking the orifice to 40 sq. inch. I can always trim out a larger area next year if this smaller area starves the tomatoes for water.

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Raybo

Thanks for the pics of your design. I'm planning on making a couple similar to these, but not sure which container I'll use quite yet.

As for the probe, I've seen them in the stores and wondered if they would work. Wouldn't it give a relative reading if you "calibrated it" by measuring the current through your chosen growth medium properly watered?

fritz,

Sorry about the photo without explanation. That is not a probe - - it is the automatic watering system (AWS) from the EarthBox Company, that I modified to work in my deeper EarthTainer design. Now, I never have to manually water my 25 'Tainers....

Raybo

Raybo, I was referring to the comment about the moisure meters being inaccurate, not your autowater setup.

But speaking of the auto watering, do you just keep the bottom reservoir filled? Or does it have to drain some before filling it? And is the sensor electronic or mechanical?

Fritz,

I have the AWS holder pipe cut to 15.25" which keeps a constant 5.25" of water in the reservoir. The level on/off is sensitive to about 1/8" change in level.

The sensor / filler is a remarkably simple pneumatic diaphragm that is "open" in the relaxed state, and as the air trapped in the cup is subjected to the increasing pressure as the water fills outside the cup, it closes the diaphragm at a set point. The beauty is that there are no moving or electrical parts at all!!

Look up Bernoulli's principle to appreciate how simple and elegant the EarthBox Company's design is.

Raybo

I was thinking that if you are using an automated watering system, why not reduce the water reservoir to and inch or two of water? Maybe 3 would be ideal?

The reason? More room for mix since tomatos seem to need a lot of room/soil to grow well.

Without an AWS it could be difficult to ensure there was always enough water of course. A small reservoir could be a problem for those that have to water by hand.

I guess the norm is 5 to 6 inches because that is the height of the pond filter. Just wondering if that is really important or something you went with because of convenience, meaning you didn't have to cut the filter shorter?

Mark,

I wanted to both use commonly available components to construct the EarthTainer, as well as have a stable base for the self-supporting tomato cage system. With 6 inches depth, I calculate the water gives me a mass of approx 80 pounds.

Certainly, if you used a pond basket of 4" height you could add more potting mix in the container, but at the risk of it tipping more easily. Personal trade-offs, I guess. I used up a 3 cu. ft. bag of mix, so each plant gets 1.5 cu.ft. to play in, which seems to work for me.

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Raybo

Thanks Raybo. Your results certainly speak for themselves. No doubt it is working well for you.

I was thinking of going with a lot less water because I have 18 gal containers. The only pond filters I found were huge. If I used them I feel like I wouldn't have enough soil so I am leaning towards cutting drain pipes to 3-4 inch lenghts. I hadn't thought about the water weight helping to keep it stable. I would think the wet mix would be fairly heavy however.

One more question. I haven't seen the inside of the "real" boxes. Seems like it is just a plastic screen with holes.

Is that the reason everyone drill a lot of holes in the plastic around the pond filter? Seems all you need is the soil inside the filter to wick water upwards. Nothing much would wick up through the holes since it is above the drain hole in the side...right? Is this to allow the roots of the plant to reach down into the water? If so, wouldn't this be bad since it may rot the roots?

Mark,

I don't own an EarthBox, nor have I ever seen one in operation, so can't comment on its construction. I have traded posts a while back with "Earl" (of Earl's Faux fame) regarding the need for aeration holes, and he was convincing to me that the drilled holes let in air to the roots that in regular in-ground gardening, worms and other insects provide.

On the other hand, "Bingster" on the GW Tomato Forum gets outstanding results with just 3 or 4 holes drilled in his design. So, I followed Earl's advice and drilled about 100 or so, in my 'Tainers. With your 18 gallon containers, you might just want to use a coffee can punctured with holes for the wicking basket. The 6" drain pipe should also work well. From my personal experience so far, I would suggest a wicking area of about 20 sq. inches, or so for an 18 gallon container.

Here is an old photo showing the hole pattern I used (since then, I have cut the size of the wicking orifice down to 24 sq. inches).

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Raybo

Thanks again Raybo. Sorry for all the questions but I am getting ready to try to make a few boxes and was having trouble deciding how to do it.

I think I may make a couple similar to your design and a couple more similar to another design I saw. Then I may try one with a lot of holes and one without. Only thing is I'd have to grow the same thing in all of them to get an idea of which was working best. Not sure I want to do that but guess I may have to if I really want to compare.

I had never thought of the roots needing air. Makes sense I guess...but plants in the ground certainly don't get that much air. But maybe they need it with that much water near.