I have self-watering plant beds, and I'm quite satisfied with them. However, I also make as much use of plastic plant bags as space permits, but they do seem to have one deficiency that I would like to eliminate, or at least reduce. That deficiency is the great disparity of moisture at the different levels. I've noticed that the bottom layer can be sopping wet even while the top layer is dry. I have a remedy in mind, but before I change my planting methods, I thought I'd check to see if anyone else has any experience with my proposed remedy. My proposed remedy is to use different soil mixes at the different layers so that the difference in drying out would not be so dramatic. There are other things I've thought of: wicks from top to bottom, ventilation shafts, etc.; however, altering the soil mix at different layers seems to be most promising. Incidentally, I have been using a mix of 1/3 peat moss, 1/3 vermiculite, and 1/3 garden soil, although I'm thinking of switching to ready-made potting soil to save time.
I wouldn't use garden soil in containers of any sort even if you've mixed it with other stuff. As far as the layers of different moisture levels that you're noticing--that occurs in pots too, it's not something unique to plant bags. I'd suggest reading the sticky threads in this forum about water movement in containers--that will explain what's going on and give you ways to address it.
I like the garden soil because it adds stability. However, I'm not alone in using it. Many of the books I have about container gardening advocate its use in potting mix. In fact, my mix is exactly as prescribed in one of them.
Al's mixes will be counterproductive from the perspective of reducing watering frequency in this application because when your grow bags are resting on the ground, hydrologically speaking they are mini raised beds & will perform better with something a little closer to garden soil than the well-aerated mixes I like & suggest for conventional container culture. In short, the earth is acting as a giant wick & pulling almost all the water from interparticular air spaces. You need to make those air spaces smaller by using smaller particles to hold more water. This is an about face from what works best for conventional containers.
I should have said that I will be looking for the articles you mentioned. The only reason I haven't yet done so is because I dread the experience. My previous searches had little to show for them. I spent a great deal of time, but only rarely found what I had been looking for. Nevertheless, I'll try again.
I'm not quite sure what you are saying, so I'll be looking for articles you have written. This should be easy. Incidentally, by "conventional container" do you mean pots? Also, I might mention that I have tried punching holes in the sides of my plastic bag containers near their bases, but I wasn't satisfied with the results. The problem is that when I watered the bags, the water flowed out the holes before saturating the soil medium. Finally, I never could reach any conclusion about using ventilation shafts. I placed several perforated plastic tubes in the bags. The holes were in that soil layer of the bags that dried too slowly. However, I wasn't able to determine if they were working.They should, so maybe it's a matter of the determining the optimum number of tubes, their diameter, and the number and placement of holes. I think I'll try again in a more methodical way.
Okay, I found your page and I have printed three of you posts. That should be enough; however, if I don't find what I need, I'll explore further. At the moment, I don't think that will be necessary.
I might add that I finally decided to do something about this problem when I had plants die. They died because I hadn't watered them enough, and that happened because I thought was OVERWATERING. Why did I think that? Well, because the bottom layer was too wet. That's one of the problems with moisture layering, it can be deceptive. You don't know what to believe, the top or the bottom layers. Anyway, when I took the advice of my nurseryman and watered, the results were immediate. I didn't even have to wait overnight, the plants--surviving ones--started noticeably picking up within a few hours. Most heartening.
Actually, I remember that when my plants were sickening, I thought it could only be from one of two causes: overwatering or too much Nitrogen. I was wrong.
I try to moisten my medium before using in any container for just that reason. I think that Al means regular flower pots with a bottom and with drainage holes when he speaks of conventional containers. I have had zero luck with "self-watering" containers, some wise person here once quipped "they call them self-watering because you'll be watering them your SELF", and that is exactly how it worked out for me.
How well SWCs work is closely linked to how favorably the soil wicks, which is directly related to its particle size. Too coarse and they wick inadequately, too fine & they wick too effectively. Their biggest plus is the convenience factor, but the trade off for convenience is a sometimes too high level of soluble salts in the soil solution and lack of control over nutrition by the grower.
I get best results with and have settled on as my preferred method, fast (draining) soils and watering/fertilizing from the top, using synthetic soluble fertilizers.
I have wicks in my self-watering beds, and I have thought of using them in my plastic grow bags. Here's a picture of my main SWC. It works just fine. Oh, I just remembered. What's "thread hijacking". Picture later.
Here's my main self-watering plant bed. It's roughly 4'X8'X2' and the water level is 9". You'll notice a drainage hole at the top of the water layer. I laced wicks throughout it when I built it, but who knows how long they will last. It was my first construction project, and I'm shamelessly proud of it.
I just now saw your postings. Thanks for the kind comments. I wasn't sure I'd be successful because the sides are of 1"X4", but the models I followed used 2'X4". That's why I placed the supports (also 1"X4") at mid-point. I was worried that the bed would push out at that point, but there was no such pressure or movement. From now on, it's 1"X4" for me. Oh, the color is something else. The wood is actually white pine, but it turned that beautiful color after I coated it with a very toxic termiticide with a transparent coating above that. I had to coat the termiticide because it has such strong smell, and because the people who follow me might not know about the toxic layers. It was actually even more beautiful, but it has faded a bit. I guess i'll give it a touch-up.
Thanks for the links, but I had already printed three of Tapla's articles, including these two. However, I have to admit that I haven't read them yet. I'll do that tomorrow.