French Intensive and 24 inch deep raised beds?
I realize a lot of people here are devoted to Mel's Mix and Square foot Gardening ... BUT, I am hoping that someone who has tried or uses French intensive or deeper beds can give me some insight into their gardening, too.
I tried SFG last year with mixed results. I love the idea of intensive growing. But overall I think the 6" of planting depth simply wasn't enough for my particular growing situation (i.e. Raised beds/plywood bottoms on wheels over extremely hot concrete patio that got to 100 throughout summer.) I also think I didn't water effectively, so there's also the user error component. :-)
I also generally like Mel's mix but prefer more than 1/3 compost.
Anyway, I'm getting ready to build more boxes over actual ground (i.e. in contact with native soil) and am debating how deep to make them.
Reading a bunch of the "French Intensive" references, they say to "double dig" to a depth of 24" so roots have a lot of room to grow down. Even when you build a 12" box/frame, the assumption is that the roots grow down into the native soil below the wooden border as they need to.
Well, in my case, for a variety of reasons, I really don't want to use my native soil. Not the least of which is a serious gopher problem, so I need a distinct "box" above ground that I can attach the hardware cloth to. But also, we did some excavation of the yard for some construction last year, so the soil has been compacted and is a lot of hardpan and compacted clay. And finally, long story short, there may be a smidgen of a chance of site contamination... our house was owned by am old jeweler who did a lot of work here on site and I think he may have "tossed" some of his waste into the ground out there over the decades. It's just a suspicion, but I'm reluctant to grow too close to that soil.
So here's my thought for trying more of a "french intensive" approach, but above ground. I would like to build 24" deep boxes (2 rows of 2x12's), so the boxes are deep----plus the 24" is a nice height for my back.
I KNOW Mel advocates shallow depth and 24" might seem like blasphemy, but I'm wondering if anyone has tried it? Or anything more than 12". (I'm getting contractor's pricing on the lumber so the price difference between 2x12"s and 2x10"s and 2x8" is minimal.)
For the soil, I'm bringing in a rich mixed compost from a local soil company that sells by the Cubic yard, which is a very affordable option. I may or may not mix in the vermiculite... I may see after I grow in it a season.
I know the bottom 12" will compact over time, but I can keep the top 12" loose and compact with regular amendments of compost.
So, am I completely nuts? (OK, don't really answer that. LOL) What I really am asking is, can boxes be "too big"? Are there any potential pitfalls of a deep box? I realize some people will say it's wasteful and unneccessary, but aside from that fact, will it work?