From: GC.SUL@forsythe.stanford.edu (Sullivan)
Newsgroups: rec.gardens
Subject: Re: hillside erosion
Date: 10 Nov 1992 16:48:35 -0800
Organization: Stanford University
NNTP-Posting-Host: morrow.stanford.edu


    : rogerv@sco.COM (Roger Vortman) writes:
Subject: Re: groundcover for steep hilside w/cement



>       My wife went to a local nursery and talked to the resident
>       landscape expert who when she found out we were putting cement
>       in the soil said she didn't want to be involved! Even for money!
>       We are in the process of rebuilding the slope. We had ivy on the
>       slope for 25 years with no problem. It appears that the slope
>       was never originally compacted properly but with 14 " of rain
>       per year it was never a problem. Last year we had 32"! 6" alone
>       the day it failed, and that on top of about 1 week of heavy
>       rain. Some people have said to use coyote bush, oleander, some
>       even ivy. The city inspector said 'no ivy'. Some say to use a
>       spray seeder, but my wife has seen two places that did that and
>       both are totally dead! We are about two weeks from putting
>       something in. The whole project is in progress right now.

Art,

I have several suggestions for you.  One is acacia redolens, which is an
extremely fast growing ground cover frequently used on slopes.  It is supposed
to be hardy to 20 degrees F.  Another is cistus salvifolia, which is another
fast growing ground cover.  Prostrate rosemary is another fast growing
ground cover for slopes.  All three of these do well on little water once
established.  There are several other varieties of cistus that work well,
hybridus for example, but that is a little taller than a ground cover.
Manzanita has several varieties that would also be good, and are quite
attractive as well.  They are not as fast growing, though, so if you want
quick cover for a particular area, these are not the plants.  They are
the hookerii variety, and some varieties of uva-ursi (or something like
that).

We have a house several slopes, the most severe being the one behind the
house.  The previous owners had a variety of iceplant established on the
back hillside that froze in the week of subfreezing weather we had a couple
of winters ago.  So by the time that we moved in (about a year ago), about
the only thing on the back slope that wasn't an annual grass were 5 or
6 small trees.  We basically denuded the hillside, leaving the trees,
and planted a combination of prostrate rosemary, manzanita and cistus
groundcovers (we couldn't find the acacia anywhere...that's what we really
wanted).  We then put in drip irrigation to get the plants established
quickly, and lots of mulch to hold down weeds, along with spraying an
anti-germination thing on the soil to hold down weeds as well.  The
landscaper screwed up a bit and planted the wrong variety of cistus on
the back slope, so after a couple of months he took them out and put in
the right ones.  With the drip irrigation only putting water on the
plants, and the mulch to keep the water from evaporating, the watering
system that we have seems quite effective at the moment.

Anyway, through judicious weeding and lots of positive thoughts, everything
on the back slope (and the other slopes, which we treated similarly) is
looking healthy and green.  Our biggest loss was several manzanitas that
couldn't take the heat and never did get established.  We had intended to
plant in the spring when it was cooler, but our landscaper dragged his
feet, and even though we started on the project in March, we didn't get the
majority of planting done until June and July.  As a result, we don't
have the coverage that we wanted by the time the rainy season is
starting (we hope to get some rain this year), but they are sort of
established.  They will probably really take off this coming spring,
assuming that we don't get any major freezes this winter (most of our
plants are hardy down to 10-15 degrees F so we would have to have a
MAJOR freeze to kill them off).

The plants that have done the best are the rosemary and the cistus.  They
have grown steadily, not deterred by heat or anything else, and so would
be my strongest recommendations, along with the acacia redolens for reliable,
no fail slope cover.  There are a couple of books that may be helpful for
you as well...the Sunset Western Garden Book has sections on problem situations,
Western Landscaping is good, lots on natives, and the book by the SF Bay area
East Bay Municipal Utility district on drought-tolerant landscaping is good
as well.

I would not use cement on a slope, what I would do is to first get the
drainage right, which may involve a retaining wall or two and a French
drain or two.  And then get it covered with drought-tolerant natives, using
only drip irrigation to get them established.  You need a landscape contractor
who understands this sort of problem, but your basic problem is to stabilize
the slope via correcting the drainage.  At that point, the plants will mostly
be for erosion control, which is a very important long term consideration.

Good luck.

-Roger

Roger, I am somewhat confused by your last paragraph as none of the
plants you listed (Cistus, Rosemary) are "drought-tolerant natives.

I guess I am really opinonated because I think it is totally wrong
to build subdivisions on hills in Southern California, then leave it
up to the homeowners to come up with some sort of solution to the
resulting erosion problems.  I think developers of new subdivisions
should be required to REVEGETATE with local native plants, and also
provide the homeowner with a list of what to plant and where to buy
it.  The loss of native plants and wildlife habitat in Southern
California is just apalling.  I saw a program on this that showed
that the practice of building on mesa tops in the San Diego Area
(leaving only canyons natural) was causing such fragmentation that
species of birds and insects were becomming extinct.

The other problem with non-native ornamentals or even species of
natives from other parts of the state is that they can become
invasive and endanger thelocal populations.  Non-local natives can
corrupt the gene pool.

I stayed out of the hillside discussion because I am not familiar
with Southern California flora and don't feel qualified to offer
opinions.  Though I would guess there might be some forms of
prostrate ceanothus, sages, or manzanitas.  Off Soapbox.  I am not
flaming you, but do wonder if you were told the plants on your slope
were native or not.

Now for some constructive help" The best source I can think of in
Southern California is TREE OF LIFE in San Juan Capistrano.  They
grow local natives and can probably help with the hillside problem

Karen

P.S. I know you DID mention the manzanitas, but don't know if the
acacia you mentioned is native
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