Sand plus clay can equal 'concrete' garden soil
Logic doesn't always apply in the gardening world.
For example, clay-heavy soils are slow at both absorbing water and drying out. Sandy soils are the reverse. So--logically--mixing the two should result in soil that's "just right."
"Wrong," said horticulturist Ward Upham. "What you usually achieve is soil with the consistency of a paved patio. You make a bad situation worse."
Upham, who coordinates K-State Research and Extension's Master Gardener program, explained.
For sand to break up clay soil effectively, the grains must touch one another--create pore spaces between their angular sides. Those spaces can hold air and/or water, thus improving both absorption and drainage.
If the grains do not touch, clay will fill the voids between sand particles, leaving no room for pores. This is another application of the principle used to make concrete, and the result is somewhat similar.
For an effective mix, 80 percent sand and 20 percent clay are generally sufficient.
"In most cases, this makes using sand to improve clay soils impractical," Upham said. "Besides, incorporating organic matter is a better way to improve both clay and sandy soils."