[eudamoniac]

I did get a soil test, but not for organic matter; I assume it's zero. My desert neighborhood has caliche under rocky sandy loam, but it also has a lot of very large old trees, so I'm hoping the caliche is permeable and not just that the original builders excavated huge holes. It's so rocky that a soil probe and broadfork is unusable, but as deep as I've tested (2 feet down) I've been able to still dig with a shovel.

This year, since I just moved in, I'm just doing a small 10x10ft testbed. I mixed in a few inches of compost manure, shallowly because the soil is so rocky. My plan is to do a biomass/nitrogen crop mix this spring, which is currently seeded, and then in fall do another similar mix along with deep rooted radish for decompaction. Then hopefully next spring I can plant real things. If I find that after a year of cover cropping the soil is still unusable, then I'll bring out the power tiller and pickaxe for the rest of the yard and get the amendments mixed in deeply. I've read a lot of permaculture books in the last year, and I'd like to garden in that way, but I'm certainly not against buying bulk amendments to get started.

12-18 isn't deep enough for me, since I am going to have large shrubs (need 3ft) and perhaps trees (need 5ft).

[krisroadruck]

We are fighting entirely different battles. The main reason I'm focused on those 12-18 inches is drainage. Heavy clay will stay waterlogged for a really long time and basically drown plants. Once it gets really dry it goes hydrophobic and cracks. But down below the first foot or so, roots aren't breathing, they are just collecting nutrients - which clay tends to have in abundance.

If you are dealing mostly with sandy/rocky soil you've got drainage in abundance. It's possible you have a perched water table with the caliche - but if it's 2 feet of permeable substrate in a desert environment I don't think you are going to be dealing with enough water for it to matter, you'll just get lateral drainage. What you need a way to slow down infiltration, and also stop leaching since the cation exchange capacity of sand is hot garbage. Shade + organic matter is probably going to be your go-to tools. Unfortunately I don't think the free arborist chips solution I did will work for you - might be too arid for them to break down in a reasonable time frame. So it's either import it at cost, or plant and wait. Just boils down to your level of patience vs stomach for paying for "dirt" as it turns out good soil isn't actually "dirt cheap".

Something to consider - most of the no-till / permaculture folks admit that a one time tillage up front isn't that bad. The main issue with tillage is you are disrupting an ecosystem. The fungal networks, the worms, all the little critter infiltration tunnels. But that only matters when you aren't dealing with dead compact degraded soil. Right now there is nothing to disrupt, so if you can combine a one time deep tillage of organic matter, or maybe subsoiling to break up some of the caliche to whatever depth you want - now is the time to do it.

[eudamoniac]

Yeah I'm totally fine with tilling at first, I was just trying to save money on renting a tiller.

Despite being sandy loam the drainage is really bad just a few inches down. I think the rocks are so densely packed together and in such great quantities that it's long to drain. I'm hoping the roots can get through and help this. If not, I'm going to have to rent a big tiller. One thing I've been doing that has obvious benefits is putting wet cardboard as mulch; the soil under the cardboard stays moist far longer. Unsightly, but definitely improving germination. I'll probably do this throughout the garden underneath landscaping rock since cardboard is essentially free.