Clay Soil on a Steep Slope

15 years ago

My most recent project was to remove the grass (fescue) in a portion of my front yard and replace with drought tolerant ground cover. The grass was planted 20 years ago when we moved into this tract home and had become patchy and ugly. We're trying to get away from having to water so much. As I started shoveling, I discovered the first problem-the trees in the front (large Camphor, patio sized pear, some unidentified tree + neighbor's Cypress) had invaded the area, intertwining their small, medium and large roots with the grass, sucking up all the water. I spent days chopping and digging out all the roots only to find the second problem about 18 inches down-a solid clay base that is dry and impenetrable. Not much I could do about that so I amended what soil was left and planted the ground cover. Now for my next project...the steep slope behind my house. When they built this tract of homes in this hilly area, they made some lots at the top and then leveled some hills and made other lots at the bottom. We at the bottom got the slopes. When we moved in, they sprayed seed including Gazanias, Sea Lavender and Poppies. Gazanias remain and a few Sea Lavender but they are time consuming as we have to go back and replant the empty spots yearly. If you picture the slope as one large rectangle tilted, and divide into thirds, the left third is a mix of gazanias and ivy that has crawled over/under my neighbor's fence, the right third is my experiment with native Salvia which has done wonderfully (I discovered a great nursery about 30 minutes away that carries native plants and picked up some sage plants last year) and the middle is hard clay with a few scraggly gazanias here and there. I want to add more salvia to this middle. I have tried using a shovel and a pick ax to loosen it up enough to dig down far enough to mix in some organic compost but can't get further than 2 inches or so. The experimental side was easier for some reason. Any suggestions? And remember, water just runs off.

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Comments (4)

ken_mce
15 years ago
If you can't reasonably dig down, what about building up? What would you think of putting in a lasagna bed (kind of a big wide sheet of compost) and planting into the compost? the idea is that you let the compost hold moisture against the clay and you let whatever lives in the soil do the work of penetrating into the clay.

You might help it along by planting a first year crop of Daikon radishes. You plant them not so much because you love radishes, but because they have a very persistant attitude about poking their root down into the soil. This leave lots of radish root sized holes into the clay the next year. After this first year of prep work you go full strength with natives and allow them to take over.

I should note that I am not familiar with zone 9. Up here in yankeeland I would expect the above to be resonably reliable.
californian
15 years ago
I bought a Bosch Brute 66 pound electric jackhammer with a clay spade to dig holes in my rock hard clay on my hill. I have used it so much I wore two inches off the end of the clay spade which is made of hardened forged steel almost half an inch thick. You can rent one at most tool rental places, but you have to be pretty strong to use it and its backbreaking work.
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If you have worms, you are better off than me. The first thing I would do is mulch the heck out of it. Then when I planted, I would bareroot the trees to correct for girdling and j hook roots and also to prevent soil interface problems. I have also noticed almost every container tree/shrub I plant is planted too deeply in the pot and the trunk flare is covered. Keep that basal flare above grade. I work almost exclusively on hillsides and there are a couple issues to deal with. You really need to control waterflow. I like zigzag swales to slow down the water and make sure a lot gets into the ground. If you make crescents, remember that they will overflow with enouh water and you need to control that. Pick an overflow location by making a low spot in the crescent and reinforce that with rocks. Also remember that hills have great drainage so you will probably want a swale above the tree as well. That will give the water a place to soak in and then travel underground to the tree below.
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Twice in one week I'm going to suggest a soil test. I rarely do that except when people have trouble growing the grass. I suspect you don't have clay in your soil, but you have a mix of mineral salts which cause the soil to act like clay. You can often fix that completely but you have to know the amount and ratio of all the salts. Only a great soil test can give you that. Or if you really have clay, the soil test will reveal that, too. But statistically 98.6238694% of people on this forum who think they have clay actually don't. I don't know what the stats are, but only about 2 per year really do have clay. As it turns out, we know just where to get a great soil test. Logan Labs in Ohio can give you what you need with their $25 test. Look at some of the other posts about soil tests on this forum and check out the kind of advice that you get for free. Also it would help if you could post a picture of your situation. I'm having trouble imagining what this looks like.
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oregongirlie
15 years ago
If you can find out what natives grew there before the subdivision, that could be a place to start. If you break up that soil, will it just wash away? Is there anything nearby that's growing well? Anything in the neighborhood you could identify and use? Usually with native plants, it's best not to mess much with the native soil. Though if it's a "leveled hill", that could be another story. The native nursery people might know what to plant.
Dan _Staley (5b Sunset 2B AHS 7)
15 years ago
Natives in highly disturbed soils don't work that well, as the original properties are gone.

Nonetheless, this situation is common and happens all the time. Usually the slope goes away and the homeowner builds some sort of wall. Don't go the cheap route and do wood - do a block wall, and not the boring block at HD. Spend 100.00 more and get a nicer block - your property value will easily absorb it and you'll be glad you did. Spend ~1/3-1/2 of your time on the underlayment and base course. "There's never enough time and money to do it right the first time, but there's always enough time and money to do it right the second time..."

Dan

Clay Soil on a Steep Slope

Comments (4)

ken_mce

californian

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oregongirlie

Dan _Staley (5b Sunset 2B AHS 7)

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