Strategies for Clay Soils
Whether you choose to amend it or embrace it, you need a
plan to plant in clay soil. Here are some tips.
By Barrett L. Kays, FASLA
C/O Barrett L. Kays, FASLA
You know the “sandy loam” plants love? That’s just the
little bit of topsoil that’s probably not even there when you start working on
the design for your site. If the site’s been graded over, you’ll often find
that the surface soil is subsoil. There’s a good chance that subsoil will be
clayey, and clayey soil comes in many mineralogical and chemical compositions.
Clayey subsoils are normally highly infertile and may have
plant-toxic levels of metals. Clayey subsoils can pose both significant
chemical and physical problems to establishing successful landscapes.
Fertilizing recommendations by soil testing labs often don’t
work for clayey soils. Soil fertility analysis as we know it was established
primarily for cultivated crops. Soil sciences use crop yield studies to
determine the amount of fertilizer to annually add to the topsoil. Landscape architects
have only one shot to do it right. We don’t plow the fields every year. We’re
dealing with highly disturbed soils. We need a whole new soil testing
procedure, but for now we’re trying to throw darts in a room with our eyes
Too often landscape architects solve their soil problems by
hauling in topsoil to hide the underlying problems. The techniques discussed in
this article are less expensive and more sustainable: Test the soil. Amend it
as needed. Break up compaction and incorporate amendments to rooting depth with
tilling. Protect that soil with fencing, with your design, or by limiting the
grading. Use pH-adaptable plants and those able to withstand the drainage
conditions on your site.
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