Do Beans Grow Better in Soil or Clay?

Soil Texture and Beans

• The question of whether beans grow best in soil or clay is misleading. Clay is a term used to describe a particular soil texture. Soil texture refers to the size of the soil particles and the mixture of different-sized particles in the soil. For example, a sandy clay soil contains about an even mixture of clay and sand particles. A pure clay soil contains more than 55 percent clay particles.

  Clay soils contain extremely small soil particles, so small that you need an electron microscope to see them individually. Likewise, the spaces between clay particles are also minute. Silt particles are larger than clay particles, and sand particles are large enough that you can see them without magnification.

  Beans will grow in a variety of soils, including clay soils. However, beans need well-drained soils in order to thrive. When working with clay soils, drainage can become a problem.

Clay and Drainage

• Because the spaces between clay particles are so small, water has trouble moving from one space to another and drains poorly from the root zone. This can cause the soil to remain overly wet, even producing standing water at low spots in the garden.

  Ideally, space in the soil should consist of equal parts water and air. Plant root systems need oxygen in order to function, which they collect from the spaces found between soil particles. When clay soils fill with water, plants may become starved for oxygen, grow poorly or even die.

Improving Clay Soils for Beans

• Adding organic matter to a clay soil can help improve drainage, making the soil good for growing beans. Organic matter includes compost, livestock manure and plant matter, like mulch or cover crops. The organic matter reacts with the clay particles in such a way that the particles stick together, forming clumps. This opens the space between particles, allowing water to drain through more easily.

Beans and Other Soils

• Beans require average amounts of water, and especially during germination and the first weeks of growth, you should keep the soil evenly moist. If you have a soil high in sand, keeping the soil moist may be difficult for the opposite reason that keeping clay soils drained can prove challenging: the large spaces between sand particles allow water to run right through, leaving the soil too dry for good growth. Adding organic matter helps sandy soils to hold onto more moisture.

  Beans need medium levels of fertility in the soil and prefer to grow in a pH ranging from 5.8 to 7.0.