Here are my observations.

The plastic cover on an SWC is not watertight. It reduces evaporation at the media surface (water conservation and reduce build up of solids) provides shade and allows the wicking water to reach the roots near the top. Some use straw or mulch instead of plastic. For SWC designs like the Earthtainer, any rain water would trickle down through the media and out the overflow with or without the plastic cover.

Without knowing more, I would say your design is not a self watering raised bed. You are missing the aeration bench, separation of water reservoir from the media and ability to changeout the water. Wet compost will collapse quickly in the bed.

What you have described will be goopy mess because the bottom of the media will always be saturated and will go anaerobic. (IMHO)

Rick

I tried one without the plastic(thought it was a nuisance)and the local critters had a great time digging in it and throwing media out of it. I do cover the plastic with fir bark to improve the appearance. Al

Good input from both of you. I know what you mean about the local critters, as my chickens are free range and love to scratch in the garden. I'm counting on tomato cages in the boxes to help keep the chickies out. The dogs liked to dig in my raised beds as well, so I ended up having to put a cattle panel over the top to discourage two and four legged critters. Chickens love to eat tomatoes also, so I have had to make the lower ends of the cages chicken proof as well.

Rick, Thank you for explaning the plastic cover better and that mulch can be used instead without damaging the wicking properties of the bed. You make good points about aeration. The raised beds will have drain holes at a height half inch below the ag drain pipes. The water should not get higher than that, so some aeration would still be present over at least half the bed or more.

While the bed will not be 'drainable', the Australians call them 'wicking worm beds', and there are good online references of doing beds this way. They also intentionally let the beds go dry a couple of times each year as a control of misquito and other types of undesirables.

For me, this setup would be designed to store water between rains, making it less frequent to actually have to add water myself (I have to haul water in a tank to the garden). I would also hope that it would help maintain a constant water supply to reduce 'spliting' of tomatoes from a heavy rain. Can you tell that I have tomatoes on the brain?
Carol

Carol,

More information helps.

I assume the drain is a half inch below the top of the perforated ag pipes. I also assume standpipes will be used to fill the ag pipes and help with aeration.

Here are a few thoughts.

I would not put any compost between or below the pipes. It will go anaerobic. Instead use small size redwood bark and peat moss as the wicking material. Make sure the wicking material is mounded slightly to ensure good contact with the weed barrier over the pipes.

Consider using braided rope wicks that extends from the inside bottom of the pipe up through the weed barrier and into the media.

Good Luck
Rick

Thank you again, Rick, for these recommendations. The redwood bark sounds like an excellent idea. Many of the Australian worm wicking beds use a product called scoria next to the ag pipes. I had to look that up. It was a volcanic rock, and I am unable to locate a local source so far. The redwood bark sounds like an excellent substitute.

You are right that there would be a standpipe for filling the bed when necessary, as well as the overflows. The rope for wicking sounds like it might be good insurance to help the system function fully. Can you advise the fabric of the rope? I'm thinking nylon, for example, would not wick? How far would it wick? Would I run it the full length of the bed above, or just a short distance with multiple wicks?

I was able to buy eight 5gallon bucket SWCs from someone locally who did not have much success with them. They seem to have been constructed exactly as online videos recommend. I want to add some compost to MG mix in these buckets and add worms for additional aeration and soil enhancements. It just bothers me to have a steril media to grow my plants in.
Carol

Carol

Here is a few suggestions,

First you may want to look for the drain pipe sock to keep the water clean. Most big box stores have it, right next or close to the drain pipe. It is a good wicking material.

Just cover the pipes with the "sock" and tie off the ends.

Some Aussies use sand around the pipes. You may want to look at hydroton (expanded clay pellets to put down around the pipe. Most hydroponics stores will carry it.

vermiculite and perlite, my understanding is vermiculite for moisture control and perlite for air.

I've grown tomato plants in hydroponics with hydoton as the media to hold the roots in place.

Al may chime in about using the 5-1-1 mix, but I think that if you are going to do araised bed with sub-irrigation that is a close system like a tote or container you may want to go without compost.

Stan

The sock sounds perfect, Stan. I'll check it out this weekend. I'm very rural (in spite of being only 20 miles from WM corporate headquarters)and no hydorponic stores. Sounds like way too heavy to order... but interesting.

No word of encouragement so far that earth worms would be able to keep compost from compacting........ Sounds like I need to go back to the worm wicking beds and study them more. Thanks so much for the help.

"You are right that there would be a standpipe for filling the bed when necessary, as well as the overflows. The rope for wicking sounds like it might be good insurance to help the system function fully. Can you advise the fabric of the rope? I'm thinking nylon, for example, would not wick? How far would it wick? Would I run it the full length of the bed above, or just a short distance with multiple wicks? "

My experience is rope will wick forever down but only about 6 inches up. I choose braided polypropylene rope about 3/8 inch diameter. Use rope like climbing rope not like water ski rope. Put a few rope samples in a jar with water and see which ones get wet the highest.

As long as the wicks get up into the media, it should work. I think the references you posted limited the depth of the bed to 300 mm. This is probably the limit of the wicking capability of your media.

For your smaller buckets, I would use a soiless aerated media and not add the worms. No place for them to hide from the heat.

Hope that helps,
Rick

I see what you mean about heat in the buckets, Rick. I have not used containers as small as 5 gallon before and heat could very well be a factor. Many of the Australian boxes were made of styrofoam, and heat may be why that is a container of choice. I see some experimentation with styrofoam coming up. :)

I'll buy a few types of ropes and try your experiment. The losers won't go to waste - there is never too much rope on a farm.

The garden beds I'm experimenting with are not to save space, or really so much about having to haul water. I'm just getting up enough in years to want to do things an easier, more efficient way. The container gardening for me started after a new hip replacement. But I'm really not trying to pick any fights with Mother Nature.