How to shore up part of a hill?

heathmitch(Sunset 21/22 CA)July 27, 2005

Hi --

I've been struggling with (and learning about) my steeply-sloping, ghetto-terraced (ancient wood planks held up by stakes made of machete-chopped tree branches in earthquake country, anyone?), clay-soiled, ivy and tree-of-heaven overrun "garden" since we moved in a year and a half ago, and my question is this -- I have some cement stairs that go almost all the way up to the flat area at the top of the garden, but at the top of the stairs there's this weird sloping depression where the soil must have washed away a zillion years ago and you sort of have to pick your way up to the flat area (climbing back down is sorta scary, especially if the clay soil is wet).

My question is this: how can I fill in that depression? Will bagged soil/mulch/gravel be OK if it's tamped down hard enough, or will it just wash away in our rainy season (it won't rain here for another 4-5 months)? Should I ... I don't know, pour concrete there, or something? Grow some sort of wicked-sturdy groundcover over it? Just ignore it?

Any advice would be greatly appreciated,


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maine_gardener(Z 5 Me)

Maybe if you put in soil and just planted grass in that spot the grass would prevent it from being washed out again when it rains.

    Bookmark   July 28, 2005 at 8:34AM
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is there any way of you taking a picture of that? I THINK I know what you're describing, but I don't have DH's visualization skills.

and if it's steep enough to make footing weird, fixing it (putting a landing in, leveling the ground, stepping stones, or real concrete work) might be worth the bother-

but I so know what you mean- it was mildewy roses and grapes on mine, though thankfully there's no slope to deal with.

    Bookmark   July 28, 2005 at 10:18AM
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heathmitch(Sunset 21/22 CA)

Well, my camera's software doesn't like my computer, so ... no pictures, sadly. And I don't think I could grow grass on it .. it's hard-baked full-sun So-Cal clay ... to plant anything, I'd have to dig it up and amend, and I'm worried about destabilizing the slope as it is.

Perhaps (sigh) I'm going to have to call in a professional for this one. Thanks for the suggestions, though!

-- Heather

    Bookmark   July 29, 2005 at 1:43AM
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vetivert8(NI-NZ zone 9a)

When you look down your slope - where did the debris from the slump end up???

If the slope continues on past your garden boundary - what's above you?

I have this picture in mind of quantities of water coming downslope in the wet season, getting in behind a slice of clay and slumping gracelessly toward the bottom - where I'm guessing your house is sitting.

Within the last couple of years we've had some serious 100 year weather events and scenarios such as the one I've outlined are reality - even on old clay cuttings that have been stable since early last century.

If you get a combination of wet weather plus an earthquake then some forms of clay turn into jelly for a while.

It may not be elegant but it should get you across the dip so you can work further up the garden - you might want to install the sort of boardwalking that gets used in national parks for crossing sensitive or sloshy areas on a walkway. Rot-proof rounds driven into the soil for at least a third of their length. Joined by long 2x4s with planking on top - used widthways to reduce the bounce! as you walk.

What you've probably got showing is an infertile subsoil that isn't very weathered yet. As you put the Ailanthus(?) through the mulcher you could add some of the mulch on the bare patch to start forming a pad of humus.

When that has formed you could look around for 'pioneer' shrubs - ones that grow quickly, even have a tendency to weediness, and can cope with the dry. There are also plenty of plants which will do the same. Perhaps even Californian poppies... I know they grow in very difficult soils.

Meantime, do keep an eye on what the water patterns are for that part of the garden, and what the impact might be of removing too much cover - however scruffy - from such a fragile slope.

    Bookmark   July 29, 2005 at 4:34AM
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