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Does Sand Improve Clay Soil Drainage?


My childhood home sat atop a bluff overlooking the Mill Creek Valley near Quincy. The view over bucolic farm fields and pastures likely was the kicker for why my parents purchased the property. It is a view that still holds me in a trance whenever I'm visiting my folks. However, the bluff upon which our house resided, was comprised of thick, red, gumbo clay!

My parents would send me out with a shovel so I could dig holes, much to my childhood delight. After all what better entertainment for a child! It is my assumption today they knew the soil was so heavy; my digging wouldn't take me down to China as I had hoped. Instead, my holes were a handful of inches. Regardless, I scraped away, with my oversized shovel. Who needs television when you have a shovel and an active imagination?

Over the years of gardening and landscaping on this property, we continually had to battle the clay soils. Only after efforts to build raised beds and add organic matter to the land with wood mulch, horse manure, and shredded leaves, did we begin to see a positive response from the garden and landscape plants.

First some hard truths about clay soil:

  1. Clay soil particles are the smallest of soil particles. Sand is the largest soil particle, with silt falling in the middle.
  2. Clay's soil particle shape is flat, or plate-like; meaning it's good at stacking on top of each other and creating a very "tight" soil.
  3. Clay is very good at preventing water from infiltrating into the soil profile, which leads to runoff and erosion problems.
  4. Clay is also very good at holding water. Clayey soils will stay wet longer than other soil types.

All these factors can create an environment that is not favorable to some plants or the gardener.

One garden misconception repeated routinely is to till sand into clay soil to break up the clay structure and facilitate better drainage. The idea stems from the fact that if clay is the smallest soil particle leading to poor drainage, and sand is the largest soil particle causing fast drainage, mixing the two will equal out to well-drained soil.

Unfortunately, it doesn't work that way.

When sand mixes with clay, it creates a soil structure akin to concrete. To create a real change in a clayey soil structure, you would need to add a 1:1 ratio of sand to clay. Considering the actual volume of clay soil underfoot, that equates to a lot of sand.

It is far more practical to use organic matter to help break up clay soil. Compost is your best bet, but organic matter can come from other sources like wood mulch, composted manure, shredded leaves, or even cover crops.

And sometimes the best course of action is to accept your lousy soil and use plants that prefer clayey conditions. Yes, these plants do exist! Plants such as columbine (Aquilegia canadensis), New England aster (Aster novae-angliae), purple coneflower (Echinacea purpurea), blazing star (Liatris), and many others will tolerate the sticky, wet mess of clay soils.

I suppose that if you do opt for the sand method, it does help to have a child with a love for digging holes, and lacking the sense to know any better.


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