Steep slope no place for slick top dressing!
Let's avoid some pain and advance as a group by pooling our
blunders. Here's a mistake we've learned to avoid -- the hard way!
--playing out on a much bigger scale and more visible place. Wonder
how many motorists are noticing and learning?
Steep highway embankments along below-grade freeways are a major
concern to transportation engineers. Plantings there are vital to
stabilize the slope, muffle noise, and provide visual relief.
Right: The presence of shrubs and groundcovers also
eliminates mowing, an inherently dangerous job on such steep
terrain.
Slope isn't the only challenge, either. Heat is a major issue.
The slope at top right on this page faces due south. It warms and
dries earlier in spring, heats more in summer than this north face.
We've seen spontaneous combustion of the mulch layer on that type
of hill, during a summer heat wave.
Give a nod to those road crews
Highway landscape crews do amazing things on steep slopes amid
breakneck traffic and gut-churning noise. Much of their planting
takes, successfully stabilizing the soil, eliminating mowing,
buffering the noise and beautifying the ride. But when these big
"gardens" slip, the fix is even harder than the initial work.
We've watched some slips go through repair and renewed
erosion for decades, noting one after another surface treatment
applied, only to fail again. Lesson? When the base is flawed, the
veneer can't hold.
Watch and learn, or sigh in relief
We who have smaller areas and slopes less steep should watch,
count our blessings and learn.
Mistake #1: Loose soil over hard
Many factors combine to cause or allow erosion. One major
contributor is this week's featured mistake: Loose soil added over
hard packed soil. Those embankments were graded with heavy
machinery before being blanketed with a soil-compost mix, and
mulch. Water that permeates the new layer slows and puddles when it
reaches the underlying hard pan. It forms a slick a few inches down
that can move everything above it like water floats a boat.
Whether you're on level ground or a hill, it's important to
loosen the original soil before adding new -- even if all you can
do is to scrape across a hill to create long, transverse furrows.
That rough contour provides a transition layer where water's
absorbed a little better and the disparate soil types and roots
have a chance to knit.
Mistake #2: Aiming for ultra-smooth
Another thing to avoid is an unbroken slope. Smooth can look
better, and we all know that looks are often be-all, end-all in
landscaping. However, terracing is ancient, simple and proven
effective -- even without structure to reinforce it.
Related information
In What's Coming Up Issue #43.
Refer to it on your copy of the Asking About Asters
CD,
Retrieve it from your personal archives (if you've been our reader
for a few years),
Or watch for it to join our Ensemble Weekly Editions here
at GardenAtoZ.com. It is "in line" and we post more to this library
every day.