Agriculture Reference
In-Depth Information
grass on the green, rather than draining away. Doing this in a home garden is dangerous
because you may create the opposite problem, which is a very waterlogged soil.
The logical solution is to till the two soils together, but it doesn't always work. It can
work well if the imported soil has a similar sand, silt and clay content to the existing soil,
but if you till the sand into clay or vice versa, the sand often gets embedded in the clay
and forms a soil environment that's like concrete. I've heard and read the recommendation
to add sand to a clay soil many times, but in my view, it's bad advice.
Besides, there's a much better way to improve clay and sandy soil, and that's organic
matter in the form of compost, sheet mulch and cover crops. Work two to three inches of
good compost into the top of a clay soil and it will improve infiltration and probably the
amount of air and water available to your plants. Wait until the clay isn't too wet or too
dry, otherwise you'll make the situation worse. If you don't have compost, other organic
matter will work as long as it's finely ground up. Ground corncobs, buckwheat or rice
hulls, peanut shells — anything that can be incorporated well will help to improve the
clay.
As an aside, for the most part, no amount of organic matter, rototilling and aeration will
fix a serious drainage issue such as flooding. That needs to be addressed by installing
drainage tiles, swales or ditches, or even better, work with nature and put in a pond. So-
metimes this can be fixed by balancing the nutrients in the soil to create a soil that drains
better, by using the nutrient ratios previously outlined.
Since we've been learning about how water moves through the soil, I'd like to mention
an interesting side note about patio pots. Gardeners sometimes put a layer of gravel in the
bottom of a container to improve drainage, but as we've seen it often does the opposite.
The soil on top may have to become very saturated before the water will drain through.
This is not necessarily a bad thing if you want the soil to hold more water, but it's import-
ant to know how this works.
So, if you need to bring soil into your yard in order to build your garden, I recommend
you incorporate it into the existing soil extremely well. If you just drop it on top, you're
potentially creating an interface that will slow drainage. Also, try to find a soil that has a
similar texture to your existing soil. For example, if your soil is clay, bring in a clay based
topsoil rather than a sandy topsoil. Also, use compost for at least 25% of the mixture.
One product that can be useful in some gardens is zeolites, a type of clay. Unlike most
clays, which are sheet-like and easily compacted, zeolites have a honeycomb structure
that stays intact. Probably their biggest claims to fame in horticulture are their exception-
ally high cation exchange capacity and their resistance to the shrinking, swelling and com-
paction that happens with many clays. There are many additional benefits that zeolites
provide, such as providing a high water-holding capacity, supplying minerals, and tying
up certain toxins. A study out of Ukraine used zeolites to immobilize lead and zinc, with
some success.
