How Do I Manage A Garden With Clay Soil?

Did you already amend the soil using sharp sand, peat moss, and/or gypsum?

Do you have alkaline soil (pH above 7) in your garden?

Is your soil deficient in calcium and/or high in magnesium?

Even if you have added huge quantities of sharp sand, peat moss, and/or gypsum, your soil is likely to remain heavy. Your plants will be healthier if they are adapted to clay soils. Perennials that are tolerant to heavy soils are lady's mantle, false indigo, elephant's ear, barrenwort, cranesbill, hellebore, daylily, blazing star, beebalm, black-eyed Susan, goldenrod. Trees and shrubs tolerant to heavy soils are serviceberries, barberry, dogwood, Russian olive, European spindle tree, potentilla, Spiraea spp., lilac, Viburnum spp.

Large quantities of peat moss worked into the top layers of the soil help to improve its texture. Most peat moss is acidic so this solution is useful only in alkaline soil. Test your soil before adding the peat moss. You should feel secure about adding peat moss if the pH tests well above 7. The layer of peat moss should be at least 6 inches thick. Sprinkle it only enough to keep it from flying as you incorporate it into the soil. Work it into the top 8 to 12 inches of soil with a spading fork. If the soil’s dry, add water to make the soil and peat mixture damp. Let the soil sit for a week and then test again.

Gypsum affects clay in the same way that decomposed organic matter does. It draws particles together into aggregates. Because the aggregates are unevenly shaped, they create some pore spaces in the soil. Although gypsum contains high levels of calcium, it does not affect pH. By adding more calcium, you can balance nutrients. Other mineral sources, such as greensand or azomite, help to modify the soil structure indirectly. Their balanced trace elements stimulate microbial activity, and this, in turn, leads to an increase in the decomposition of organic matter. The more organic matter there is in your soil, the better the aggregate structure and drainage.

Sharp sand will help to modify clay soil. But If you add just a little bit of it, the soil will be even harder to work than it was without the sand. To make a significant difference, it takes the addition of 3 to 5 tons of sand for every 1,000 square feet of garden area. Also, sand alone is not as effective as a mixture of sand and organic matter. Apply at least 1 inch of finished compost to the top of the soil, just after you spread the sand in an even layer, and work both materials into the first few inches. Be sure to wait until the clay soil is dry enough to work before starting this procedure.