Hi Sandy,

I replied to your post on the veggie forum assuming these beds would be open to the earth.

With closed bottoms they should be considered large, but shallow containers and treated differently.

There is an excellent thread by Tapla (AL) in this forum I will refer you to for more details.

The nitty gritty of it is that with shallow containers drainage is of paramount importance to plant health. When connected to the earth Mel's mix drains really well, but in a container it doesn't and can't. Other than Al's thread here is a University link explaining why.

Bottom line is you would do your students a favor by recommending a free draining potting mix and water soluble fertilizers over a small particled mix (such as Mel's mix) and relying upon compost for nutrients.

Thanks, justaguy2. The article and thread clarify a lot of issues. I'll look them over closely. I hadn't considered the possibility that Mel's mix would cause a drainage issue in the closed container of a bed with a bottom. (Thanks for your explanation on the veggie forum about that kind of bed.) Since I don't have any experience with the "pure" formula, it surprised me. My primary concern was plant nutrition but I can see now that fertilizer might be lower down the list of concerns. Plants with water logged media around the roots certainly have a worse problem than lack of nutrients.

I'm always learning.

Sandy

Just remember that YOU are responsible for ensuring your plants get a full compliment of nutrients in a favorable ratio. You can't depend on the soil to provide them. On a scale of 1-10, with 1 being growing in the garden and 10 being hydroponics, container culture is probably a 7 or 8. That is how different gardening in containers is than growing in the ground.

Growing in a raised bed pretty much follows the rules of conventional gardening because the earth acts as a giant wick to 'pull' moisture from the raised bed soil - containers are much different.

Al

Does Mel suggest lining the beds? I have his books but don't remember this--I thought you just put newspapers down which would break down.

I would not line the beds with anything permanent or as Jag says it is just a shallow container.

In his book he doesn't recommend lining the beds, but he presents it as an option with no repercussions to the plants.

I respect the work Mel has done and is doing trying to help people grow their own food, particularly in third world nations, but it's just not true that a bottom can be placed on the bed separating it from the earth with no repercussions to drainage (As I know you know, Farkee).

Mel suggests that these beds can be built up on legs to make them wheelchair accessible or they can be put on hard surfaces such as patios or driveways. That would give them a solid bottom and make them "containers" rather than the more typical raised bed with soil beneath. It was this type of bed that concerned me most regarding fertilizer but, thanks to the knowledgable people here, I've been alerted to the drainage issue.

The information by Al is just superb. I've always thought that the gravel in the bottom of a container and/or the drainage holes made the soil less likely to become water saturated. But then again, I knew about perched water tables in native soils from our line of work. I just never put it into a container.

I do have another question after reading Al's information. How does the wick work to remove excess water? And why doesn't gravel in contact with the bottom of the soil layer do the same thing? I know a little bit about capillary action but not enough to understand this. I know I'm showing my ignorance by asking this but I'd rather ask and look dumb than not ask and look dumber! LOL

Sandy

Sandy - as soil particle size increases, the level of perched water in THAT material decreases, until at around 1/8" particle size, the PWT disappears entirely. The problem is in the fact that if the "drainage" layer is more than 2.2X the size of the soil particles, the water will 'perch' in the soil.

An unscientific explanation that's easy to understand: The wick 'fools' the water into behaving as though the container is deeper than it is. The perched water 'thinks' the container is actually deeper, so it travels down the wick looking for the bottom of the container. When it gets to the bottom of the wick, the water traveling down the wick behind it pushes it off the wick. If the conditions are right, and the soil is not too water-retentive, the entire PWT can actually be contained in 2-4" of a very thin wick dangling outside of the container.

I'm glad you asked - I hope that clears it up, if not - ask again & I'll try a different tack.

Al

Al, I understand most of your explanation. The only thing I don't quite get is the part about the particle size greater than 2.2x the soil particle size causing the effect to no longer work. This would mean that gravel wouldn't work but would something smaller such as sand work, or at least work better than gravel? Or is that still too large? Also, there's a product called Permatill which has rather small particle size. Would that work in place of larger gravel? Or is it still too large also?

Thanks for taking the time to help me with this problem. I want to be able to give my students what really will work if they choose to make these beds with solid bottoms without them having to spend excessive amounts of time and money building specialized soils. I'd hate for them to lose plants due to MY ignorance!

Sandy

An aside from my (very limited!) research on capillary action...

Excess fertilizer (salts) causes negative water potential in the soil with "less" negative water potential in the plant so the water moves from the plant to the soil instead of the other way around, causing the plant to wilt or "burn." Is that right? Or do I need to go do more reading?

It was Mel's book that got my husband and I gardening over 25 years ago so I really appreciate his work. I read that 'Square Foot Gardening' is the number 1 selling garden book of all time. I don't really follow all the dictates now but it sure helped in the beginning when a big traditional 'row' type garden we tried failed miserably.

It was also the picture of the wheelchair accessible garden in Mel's book that gave me the idea of raising long containers up on legs 15 years ago.

I took an organic vegetable gardening class from an organic farmer who used raised beds made of concrete blocks who recommended a mix of 70% coarse sand and 30% muck or top soil (later to be amended with compost). Extension agent and college hort instructor also recommended same thing. I had it tested when 18 yards arrived and of course it was bereft of practically everything but I add compost and other organic matter every season.

Also did 25 raised beds at Homeless Shelter and we used same 70/30 but what was delivered was also very rocky. Worked great--the peppers we grew were phenomenal as was everything else.

Forgot to mention that at the shelter the day the beds were filled I brought 25 bags of peat humus and 13 bags of cow manure so each bed (4' by 8') got one bag of peat humas mixed in and 1/2 bag of cow manure.

Lol - I was going to suggest we take the discussion to the Water Movement thread because we were walking all over the OP's thread - then I realized you were the OP - so I guess we can talk about whatever we want to - huh? ;o)

I think you need to lose the idea that a drainage layer is a good thing. Using something finer than the soil in a container bottom to make the soil drain is problematic because, like it or not, the fine layer becomes part of the growing media and roots won't like it.

You CAN structure your layers so that you can use layers of increasingly larger particles to facilitate drainage, but practically speaking, it isn't workable for the average grower. It would entail layering particles one over the other so the particles in the upper layer are no smaller than 2.2 x the size of the particles below.

If you have a drainage layer that works, either the particles in the drainage layer are so small that they won't support good root growth/metabolism, or the soil is comprised of particles large enough that no drainage layer is required. The latter scenario is the basis of how all my soils are formulated. I want them to be right at the meridian between a soil that does and a soil that doesn't support a perched water table. The size of the particles in the gritty mix are all in that 1/8" range (no perched water at all) and the average size of the particles in the 5:1:1 mix are just a little smaller. That's no accident. ;o)

Making the beds with a solid bottom, but with a few hols so the soil forms a bridge between native soil and the soil in the beds will find you growing in a raised bed that acts like a garden. If your beds are on concrete, or the bed is raised (air underneath) or has a solid bottom, it will behave like a container. The difference is that in the former case, the earth acts as a giant wick & 'pulls' all perched water from the beds, while in the latter case, w/o the soil bridge for continuity of the wicking action, it won't.

Al

Farkee,

Are these raised beds solid bottomed or in contact with the earth?

Yes, Al, we can discuss just about anything on this thread having to do with these containers. I want to learn more so whatever will help me is fair game!

Ok, if I understand this, the ideal is a soil that doesn't maintain perched water but still holds enough moisture for plant health. The next best thing would be a soil with a very minimal PWL. I've looked at your recipes for soil mixes and they look good but I suspect the average suburban homeowner (my students) isn't going to the trouble to make up a soil with ingredients that hard to come by. Do you have any suggestions for amending Mel's mix or some commercial potting soil that will work in these beds with solid bottoms? I don't remember seeing pine bark fines in the local stores, but can't say they don't have them since I've never actually looked... on my list of things to do this weekend! Is there something else that would help that's more readily available?

Farkee, I've been gardening since I was knee high to my dad when he had a small truck farm (mumble, mumble) years ago, mostly in large row-type gardens. I knew about intensive gardening but always thought it looked like even more work than I was already doing. Then I found Mel's book and knew I had the answer for my current garden. I've gone from a 3000 square foot garden to two SF beds of about 40 sf each. I'm planning to build another bed this summer, soon enough to plant a few things for a fall garden I hope. I'll never be able to match the production of the big garden but then again I don't have a big family at home anymore to eat all of it and I don't have the energy for it either. Now I try to persuade everybody that the principle behind SF gardening is the way to go, especially for suburbanites who have flower beds that can easily be converted or all that lawn that's just pretty but unproductive. It seems to have become something of a mission in life! LOL

Sandy

Wow, again! I've been reading more of your posts on various container topics and you are just a font of wisdom, Al. I've been on other forums here for a few years but not much on this forum so I guess I've missed you before. I assure you I won't make that mistake again! It is really great to "meet" someone with such depth of knowledge who is so willing to share it with others.

Please don't take my last post as a criticism of your formulas for soils, just inquiry into an easier to obtain mix for those less intense about gardening. I'm mostly talking to people just starting out vegetable gardening, not people like some of us who are already passionate about the subject.

Many thanks, Al, for sharing your knowledge and experience with us.

Sandy

Sandy,

There are a couple things you can do to try and steer your students in a productive direction. I understand that telling them to all make their own mixes may not be practical given the audience.

What you can do is go purchase a few different brands of commercial potting mix that are common in your area and your students will find easily and give each of them a perched water table test. It's very simple to do with a clear plastic cup. Fill with mix, saturate with water and poke a hole in the bottom and let it sit and drain. When no more water comes out the bottom look to see if there is a PWT and note it's height.

Simply prefer the mix that has zero or the least PWT and recommend that mix to your students.

Secondly, the use of a wick coming out of the drainage hole will assist with draining the PWT allowing the students to use a slightly less than idea media and still have good chances for success.

Oh, before I forget. Do all your students a favor and warn them away from Hyponex. It tempts lots of folks due to it's deceptively low price, but it's pure garbage.

That's a great suggestion, justaguy. Since I'm doing these classes for the cooperative extension (I'm a Master Gardener Volunteer) I can't actually recommend or warn against any name brand product but I sure could do the demo and let them draw their own conclusions. I've bought my share of horrible potting soil and other products over the years and it would be a good way for them to see what's inside those opaque bags before they buy. I'll work on this next week (after I get past the cookout we're hosting this weekend!)

Sandy

are we invited ? :)

justaguy, all these raised beds are right on the ground --about 6 or 8 sheets of newspaper was laid down at the shelter --with my own 15 raised beds at home I didn't bother with the paper.

This is a kiddie pool filled with soilless peat based mix available everywhere. Depth of soil is about 6 inches. Those are dwarf bok choy and romaine. I think the majority of your participants will want to just buy a bag premixed.

Last pics,
Raised on legs inspired by Mel B.:

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I wish GW had an edit feature--when I said the majority would rather buy premixed I meant for containers--It would be awfully expensive to go that route for raised beds.

Of course you're invited! The more, the merrier, especially gardening nerds who promise not to criticize my weedy lawn which would be all veggie beds if I had my way all the time. Offerings of food and beverage accepted at the back door. (No offense meant but one of the agriculture gurus at VA Tech is very proud to call herself a plant nerd!)

Farkee, that's a beautiful batch of lettuce! And I like the bed on legs. Would you mind sharing the construction details of that bed? I've always worried about this kind of bed not being stable enough with all the weight.

Sandy

Those are about 8 years old now. I had built elevated beds made completely out of wood before but I asked a friend to design and build these using 21' drainage pipe cut lengthwise. You must carefully brace in the middle and I have even beefed up those braces with extra wood. They are 10 feet long. Use a light soilless mix. The soil can be reused year after year just 'refresh' with new mix. Only attempt if you know you have it sturdy and it won't fall over sideways. I enjoy building 'stuff' myself and have made several more elevated containers --easy on the back --planting and harvesting.