My PH results came back as 8.4, 8.1, and 7.6 in the garden areas I want to plant, and the extension office says I need to bring it all down to 6.5.
I have to sift large rocks out of the soil to separate it from the clay. I don't know which raised bed strategy would be the best for my environment. I'm thinking of going with the temporary type, but I'm not sure yet. I really wanna get this project off the ground before its time to plant.
My environment is high desert in a very windy area. I might consider building some high tunnels.
Anyway, how much compost do I need to amend this soil that's virtually 100% clay?
As for loweing PH, my extension office wasn't very specific. They just said to add 3-5 pounds of sulfur to every 100 sq ft. to lower it.
Any kind of compost, except composted pine needles, will help bring down the PH. If the rocks are limestone removeing them will help keep the PH down. As you are sifting your soil that is a good time to add the compost, it helps keep the clay broken up.
The raised beds will drain better than a surface garden and keep your soil amendities more concentrated. In your case this could be good and bad. Draining well will allow some of the alkali to be washed out, but with windy conditions you may need to water more often. A wind break would help that.
There are too many new and different mistakes out there waiting to be made to be wasteing your time repeating the same old mistakes.
Low rainfall nearly always means a high ph and I think just trying to get it toward neutral would be a hell of a battle. 6.5? Not likely! I'd focus on plants that can handle heat and high ph and just keep adding as much organic matter as you can. Don't be hankering for blueberry bushes...
I'm not a fan of raised beds: irrigation is a nightmare in dry climates. I've gone down, rather than up. Check out sunken beds: you'll have them anyway after you've dug out those rocks
While your environment sounds pretty difficult, clay that's looked after is wonderfully fertile and water-retentive. I'm on a sand dune and it's like pouring everything through a sieve. Easy to dig though...
I often have gales and they suck the life out of plants. Good quality knitted windbreak cloth is very effective. And instant. And totally environmentally unsound. Get Black, green looks stupid.
How big is the plot? I am on heavy clay and never really bothered to get it checked. ime its better to watch the land and see how it reacts. So I just started planting and adding compost and mulching really well. After 4 years of this (and decent crops of corn many greens courgettes beans and tomatoes) my ground is now a lovely water retaining composty clay that is a pleasure to work with. The front garden which I have only recently started to deal with is still like the back was a few years ago. I am treating this much the same lots of plants lots of compost lots of mulch and I trust that it will behave in much the same way as the back did
zone 8, 382.5 square meter garden 2 up 2 down 1920's ex-council house. heavy clay soil
I have clay soil with rocks. I'm digging out the rocks and replacing them with buried wood beds, not raised beds. This is more work than a lot of people would probably want to do, but my experience over the past year indicated to me it is worth it in my situation.
This hole was dug by mechanical excavator but the beds in the background were all done by hand. The hole is about 18 to 24 inches deep, going down to what feels like a solid rock shelf:
I think another thing to try might be to build very large hugelkultur (raised wood bed) over the entire garden area, paths and all, if you want to avoid digging out the rocks. But you'll need soil to cover the hugelkultur, so that would need to be brought in from another area.
A good friend of mine had a similar situation on a mesa of the Rio Grande in southern New Mexico....high desert clay. His first approach was to bring in a truck load of sand because sand+clay eventually makes soil. His second approach was to source mountains of aged horse manure. This became the basis off all his raised beds, which were formed with cinder blocks and lined with hardware cloth on the bottom and the top to keep critters away from seedlings. His third approach was to have a group of geese and ducks that had their own little pond. Water from the pond was pumped into the beds as a fertilization. His fourth approach was to buy truckloads of spoiled hay for basically the price of transportation. This was used to heavily mulch everything. The moral of the story is almost all of his initial fertility was imported. Once he began to establish perennials and good soil, it was like dominoes and his fertile zone expanded as he continued to pump water onto the property and trap rain water that would have run down the slope.
Just some observations from someone who has seen an attempt at permaculture in a similar environment
I have clay soil on a north slope. I was wondering if you have to till anything if you lay the material that prevents weeds inside a raised bed. It does sound like a clay mixture would be better but I really don't have time this year.
I have clay soil. I've found that working in organic matter (my situation used fallen mulberry leaves) loosened up the soil in more than one way; it got broken down by the worms tunneling. A quick dig down in areas with little leaf matter worked in showed heavy compacted soil. In patches that got the leafy TLC, a clod of soil would show tunnels going every which way and with a little squeeze of the hand, would crumble. Making my clay soil into a welcoming place for worms has done much to improve the soil itself and the health of what I grow.
If you need aeration, then working in organic matter should be high on the totem pole. I don't know if sand worked in would be as beneficial as some nice, healthy compost/worm castings... but vermiculite or perlite could do the same without the worry of cementing the soil.
Clay soil is second only to organic matter in the amount of nutrients it holds. It is really good, just a pain to work as it must only be worked, or traveled on when it is at the correct moisture level.
On your exposed site, I would not use raised beds as mentioned before they will dry out so much faster. I would mulch the beds areas with compost and go for it. I would remove the biggest stones out of the way first.