Are the boxes open on the bottom?

Many folks have pretty good success growing in 100% compost. In my own experience, I have found that clay is not as bad a growing medium as some would have you believe. It can be easily compacted, so walking on it as little as possible is rule number one. But, it also has very good moisture retention, nutrient retention and adds a good base for roots to be able to anchor in. If this was my garden, I would probably amend my existing soil (removing as many of the large rocks as possible) and go with the clay/compost mix.

As an aside, my yard is ALL clay, beneath about 3 inches of top soil. I thought my garden was doomed when I first saw it, but I have amended it for 6 years now (4 years before I started to SFG, and two years since). My garden NOW has a nice loam to it, more worms than I care to count and my veggies couldn't be happier (if they have any type of emotion!). My amendments were peat and compost. (In the last year, I added some vermiculite to the mix, as I was finally able to track some down that wasn't more expensive than I was willing to spend.)

Everything grows well, although last year's "cold" summer had an adverse effect on my tomatoes and peppers.

Anyway, welcome to the board and don't be afraid to fail. Just try something. Failing to try is trying to fail!

I agree 1000 percent with EG about clay soil. It gets a bad name but it has the best Cation Exchange Capacity (ability to hold and transfer nuits to plants) of any soil and drains fairly well. It seems to hold moisture in real dry weather. The biggest negative is it tends to take longer to dry out and CANNOT be worked when wet - unless you want chunks of dirt that can rival rocks in hardness.

I had to build a raised bed this year and used dirt that has a fair amount of clay, aged horse manure and compost. I won't know for sure how it will finally turn out until later this summer but so far, of the 30 veggies I planted in it, the only ones not looking super fantastic are the Jicama and two Swiss Chard plants. This is despite one of the wettest Junes on record. Not one big storm, just a couple of downpours (1-3") per week.

Mike