Soil preparations for raised beds

[cactus]

I'm undertaking a new project - developing a community garden on property owned by my church. My first inclination is to just use native soil, but I've come around to installing raised beds (approximately 8" deep) filled imported soil.

The local organization that helps community garden organizers recommends putting cardboard down on the native soil and then covering with the "top soil". Here's my question: considering that the native soil is heavy clay (yes clay, really) and will effectively become the subsoil after the raised beds are installed, how much benefit is there in doing a lot of soil prep (tiller radishes, green manure crops, humates, etc) to the existing soil prior to putting in the raised beds? I can't think of any harm in it, but I'm not altogether convinced that it will be as useful as I might think for a vegetable bed. Of course I don't believe that only 8" of soil depth is that useful for planting, so I guess I've answered my own question.

Thoughts?

[grassboro]

I have an area in my backyard (40’X 30’) which arguably may be about the most challenging clay soil that one could have with white, gray, blue, etc. clay. What I ended up doing was a cross between Lasagna gardening and Inter-Bay composting techniques. In Nov. of last year I killed the weeds with RU and started with a layer of 8-10 sheets of newspaper. I then alternated layers of browns (mulched leaves, hay) and greens (manure, coffee grounds, threw in a little fertilizer, etc.) to about 12- 16 inches. Then I covered this with burlap. I kept this moist over the winter and added free coffee grounds as often as I could. By March this had broken down pretty well and I had lots of worms!

I ended up with a successful garden. It is still is a work in progress but will get better every year. Google Lasagna gardening and Inter-Bay composting and see if this is something you may be interested in. You will see I did not follow this system totally. I did not build up as high as is recommended but I was doing it for a slightly different reason, which was to improve the existing soil in a large area without doing a lot of work so I could plant perennials down into the existing soil. You will see that vegetables are planted directly into the Lasagna beds, not down in the soil, since they don’t need a lot of root support in comparison to what some larger woody/perennial plants do.

[cactus]

Thanks for the tips. I've read about lasagna gardening in the past but had forgotten about it.
My biggest concern is that I'll be working against the recommendations of the local gardening experts who have been using simple raised beds successfully.
I'll do some research and see how these methods can fit into our program.

[grassboro]

If you have to do what the gardening police, I mean experts say then they may not like anything that deviates from their plans.

My sister had existing raised garden beds and asked me for advice last winter to make them better. I got her to dump a bag of alfalfa pellets into them over the winter. She had by far her best vegetable garden this past year.

[cactus]

Since I'm the one leading the development effort, I might designate one of the beds as "experimental" and claim that allotment for my own family. Then I shall laugh at how puny all the other tomatoes are in comparison. (Cue evil laugh...)