What to Put in Clay Soil for Planting Annuals

About Clay Soils

• Soils with a high proportion of clay seem dense, sticky and heavy. When dry, they tend to crack and may be difficult to wet. The tiny particles of flat minerals, so small that you need a strong microscope to see individual pieces, hold water and nutrients well but are difficult for roots to grow through and poor in air spaces. Clay also compacts easily under foot traffic, especially when wet. Even when the solid clods are broken up, it tends to settle back into a dense mass. Most clay soils have some sand or silt mixed in, but the clay fills in the pores and, when worked by a gardener, becomes impenetrable to most roots.

Adding Organic Matter

• Any kind of organic matter opens up clay soils, creating spaces between the grains and helping to resist compaction. Organic matter decays to a black substance called humus that binds the small clay particles together into larger, sand-like grains, further opening up the soil. Spread a layer of any kind of organic matter, peat moss, coir, compost, decayed straw or manure, pine bark humus or leaf mold over the surface of your annual bed. Spread a minimum of 2 inches of material, four cubic yards per 1,000 square feet of garden space, and more is better. Dig and mix this layer with 6 to 10 inches of the soil beneath to give the roots a deep root-run.

Adding Coarse Materials

• Many gardeners dislike having stones or gravel in their soil, but roots grow well in gravelly ground if the soil is loose and there is enough clay or organic matter to hold moisture. Sand is not a good amendment for clay, but pea gravel or slightly larger stones make clay more difficult to compact and assist with creating air spaces.

Fertilizers And Other Amendments

• A granular fertilizer can be worked into the soil with the organic matter to give annuals a quick start. Use a 5-10-10 formula, low in nitrogen and higher in phosphorous and potassium, to promote flowering since too much nitrogen leads to leafy growth and few blossoms. Bone meal, high in phosphorus, is also beneficial. Adjust the pH of the soil to 6.0 to 6.5 by adding lime to acid soils and sulphur to more alkaline ground.