Page 37 - Green Builder March-April 2016 Issue

CREDIT: USDA quick work of it.
Tilling requires turning over and/or mixing the top 12 to 24 inches
Tough Soils. As the diagram shows, the higher the percentage of
clay, the slower the infiltration rate. of soil, and is a time-honored method for loosening and aerating soil.
For more extreme cases, “subsoiling” may be required. This involves
Expand storage. Including a larger fracturing the soil at deeper levels with a machine consisting of metal
storage layer with an underdrain shanks and either pointed or winged tips.
can significantly slow peak flows
and increase infiltration, protecting You can improve drainage through grading or by altering surface
stream banks and potentially reducing drainage routes, or by amending the soil. Proper plant selection can
combined sewer overflows. mitigate areas where changing drainage and infiltration rates is
difficult (for example, in naturally low, wet spots).
Use alternative practices. For sites
for which mitigating clay soils is too As a last resort, you can remove the soil from the site. This extreme
difficult or expensive, choose features (and extremely expensive) measure should only be taken when no
that do not require infiltration. These other options are available.
include rainwater harvesting, green
roofs and vegetated swales. Soil amendments and additives. Physical, organic, biological, mineral
and chemical amendments can improve soil structure and fertility.

Physical amendments include structures such as geowebs and turf
cells, which stabilize soils within the root zone.

Organic amendments include compost. One of the best all-around
amendments, compost can improve both soil structure and fertility;
it also stimulates biological activity and promotes healthier, more

2. POOR URBAN SOILS

It’s especially important to manage

stormwater on urban lots, since

urban areas are often dominated by

impervious surfaces. But the soils on

these lots are often severely compacted,

lack sufficient organic matter and/or

contain construction debris. (This is, of

course, also a problem if you want to

incorporate other types of landscaping CREDIT: WICKO

and/or grow food.) Fortunately,

there are a number of methods for

transforming these soils. Rockhound. Some landscape rakes, such as this model from Wicko, even have hoppers that collect
Before doing anything, the soil the stones and other debris.

should be evaluated for its structure,

percentage of organic matter and possible presence of contaminants. disease-resistant plants. The quality of compost can vary, so make

Physical reconditioning. These methods physically change the sure you know the source. If making it yourself, make sure the

characteristics of the soil to improve its structure. organic materials are thoroughly broken down before using.

Raking can remove construction debris, stones, loose root pieces Mineral amendments include perlite, hadite and pumice. These

and other objects as small as ¾”. The jobs can be done by hand if commonly used minerals help create large pores in the soil through

the area is small; otherwise a landscape rake and a tractor can make which both air and water can move; they are also sterile and

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