Amending soil on steep, rocky slope - Zone 10/SoCal

6 years ago

Hi, all!

The CA Gardening and Ground Covers forums don't seem to get much traffic, so I thought I'd post here -- TIA for your indulgence.

I live in TX, but visit my mom periodically (read: I'm not around 24/7 to handle/monitor yard projects, unfortunately). She has a sandy/rocky/dry slope in her backyard. Pic 1 and Pic 2 are the extent of it, and the right side continues onward to the street (but not as sloped a section):

When my dad was alive, for decades he tended the entire yard. He planted various ground covers (albeit w/ spotty success) and a couple of juniper trees in this slope area. Since my dad's passing several years ago, my mom has been in simple 'weed control' mode. At 85, she's finally been convinced by us that she should not be climbing around up there!

Even with a small amount of misting with a hose, the water (and dirt) just comes down the slope in streams, accumulating at the bottom.

This past week, I planted six trailing lantana (see Pic 2). Digging each hole was an absolute bear -- rocky, dry, hard. I amended with some steer manure and planted the best I could. The lantana are doing great, but I have to take a lot of care misting the soil to avoid runoff.

Am I amending the soil properly? Is there a better way? I have only the local big box stores at my disposal.

Eventually, we may just have to hire a local landscaping company to plant the entire area; but I'd like to do what I can on a small scale for now. I'd also read that it's best to incorporate more than one variety of ground cover/plant to optimize erosion prevention, but that'll have to be waaaayyyy down the line. We're just trying to stabilize the hill, keep the weeds at bay, and make the upkeep (watering) easy for my mom.

In TX, mulch rules. Out here, not so much (it seems); and I'm not sure why. But I'm thinking placing mulch around any new plantings would be a good idea (?).

Lowes has this stuff:

This, from HD:

Better than nothing?

Again, thanks for any advice.

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Comments (4)

Embothrium
6 years ago
last modified: 6 years ago
Continue the terracing with blocks up the entire slope, so that all of it is stabilized enough for planting. Then apply the mulch to minimize drying of the soil, plant next winter or early spring after the soil has been moistened all winter by whatever rainfall comes next time. Other than say the middle of summer spring - apparently in this case after the soil has already dried out - is the worst time to plant in Mediterranean climate areas with hot dry summers.

Plant by pulling aside small areas of mulch for each plant as needed, putting the excavated soil in a bucket to keep it off the mulch. And make it easy to pour it back in the hole around the plant (do not modify the planting hole back-fill by adding amendments - plant in loosened existing soil instead).
javiwa thanked Embothrium
gardengal48 (PNW Z8/9)
6 years ago
Without going into excessive detail, it is never a good idea to amend individual planting holes. If you do need to amend, do so over the entire area before planting. Personally, I would add a bunch of compost or other organic matter to that slope to lighten that heavy, rocky soil and to help with aeration and water retention. Then plant with a single species of groundcover.........combining more than a single variety is seldom successful as one will always be more vigorous than the others and overwhelm and outcompete the less vigorously spreading types. Make sure it is woody based, evergreen (no herbaceous selections), low growing and drought tolerant once established. Local nurseries (not the box stores) will have multiple selections available if you are not familiar with CA plants. If in full sun, I'd consider Point Reyes ceanothus, a CA native.

And I would recommend mulching after planting. It will help to keep the weeds down while the groundcovers establish and will help to hold moisture in the soil. The smaller or finer the particle size, the less likely it will be to slough off or wash away down the slope with rain or irrigation.........look for shredded bark rather than bark chunks.
javiwa thanked gardengal48 (PNW Z8/9)
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I don't think you really want to go digging into that slope to remove rocks - you're going to contribute to destabilizing and erosion if you do that. Your slope isn't overly steep, but you don't want it eroding all the same. If you are finding a lot of rocks coming to the surface after each rain then that is a sign of erosion. Wildflowers are good plants for a slope as they can handle the marginal soil and water conditions and many of them have deep roots. Amending your soil the traditional way is a problem for this area and those plants don't really need it much anyway. One thing I would advise against is using large bark pieces for your mulch. These are likely to roll down the hill with a decent amount of rain or be pushed down with snow. They also don't break down to amend the soil which is something you sound like you do need. Shredded bark of various sizes would be a better bet. As it breaks down, worms will eventually move this new rich soil down to the rocky clay stuff. It takes awhile, but it is a thousand times easier than digging amendments into a rocky slope! Newspapers to smother the weeds are an ok idea, but they won't break down on a slope as well as they would on flat ground, and they might just slide off. Putting down a layer of shredded bark mulch three inches deep in the areas you want to kill off the weeds will be just as good if not better at weed killing and soil amendment. Planting things in behind rocks as you say you have been doing is a good way to give the new plants a secure spot to develop. It'll take two or three years for that slope to fill in nicely, so don't be impatient and plant things too close together! One thing to consider would be terracing the slope to some degree. If you have a lot of big and medium sized rocks, make little arcs of walls about 6" high and fill in behind them with your peat moss, manure and black earth. This way you can plant some larger shrubs or plants that require a slightly better soil. BP
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javiwa
Original Author
6 years ago
Continue the terracing: I'll pitch that to my brother who'll be doing the heavy lifting. Though, I think it was his intent to remove all the cinder blocks my mom accumulated over the years.

...never a good idea to amend individual planting holes: Yes, that's the advice I follow whenever planting in the Houston-area gumbo/clay. Amending as I did for the lantana was the only way to keep the sandy/rocky soil in place...it just kept sliding away. Had I the time, amending the entire area would've been the way to go -- and I'm sure when/if a landscaping company is brought in, that's what they'd do.

combining more than a single variety is seldom successful as one will always be more vigorous: good point -- got it.

Noted regarding mulch: is the bagged stuff from Big Box (I'll try to find shredded) better than nothing? Again, I'm doing a small scale experiment with the lantana for now -- we'll see how things go. I won't be back til late July, when the hillside will be in the throes of summer.

Thanks again, Embothrium and gardengal.
gardengal48 (PNW Z8/9)
6 years ago
ANY mulch is better than nothing :-))
javiwa thanked gardengal48 (PNW Z8/9)

Amending soil on steep, rocky slope - Zone 10/SoCal

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Embothrium

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Amending soil on steep, rocky slope - Zone 10/SoCal

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Embothrium

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