Do Sunflowers Do Well in High-Clay Soil?

Clay Soil

• Clay soil consists of at least 55 percent clay particles, although some soils may contain well over this amount. Clay particles are the smallest found in your soil, which has important implications for plant growth. About half of a healthy soil consists of air spaces between the soil particles. Ideally, these spaces contain equal parts of air and water, both essential for healthy plant growth. Clay soils contain abundant air spaces, but because the individual clay particles are so small, the spaces are small as well. Water often drains with difficulty from clay soils, making them more susceptible to compaction.

Sunflower Soil Needs

• Sunflowers can grow in any soil type, including clay, if you make necessary corrections to address any problems. In addition to soil texture, consider the pH of the soil. Sunflowers are relatively tolerant and will grow at a pH ranging from 5.7 to 8.0. The soil should also contain abundant nitrogen and phosphorus, both of which can limit plant growth if not present in the proper amounts. A routine soil test can help you to prepare your garden soil for sunflowers.

Soil Limitations

• The only soil conditions likely to limit the growth of sunflowers are poor drainage and impenetrable soils -- both are characteristics of clay soils. The small pore spaces in clay soils cause water to drain slowly, and clay soils can become overly wet and poorly aerated as a result. Furthermore, the tiny clay particles are subject to soil compaction, which can make it difficult for roots to penetrate in the soil. The deep taproot of the sunflower makes it drought resistant, so the health of the plant depends on its ability to tap deep into the soil.

Preparing the Soil

• You can amend even poorly drained or compacted clay soils to grow sunflowers. Sunflowers thrive when provided with compost or well-rotted manure. In addition to providing them with nutrients, these organic materials also help to loosen the soil and improve drainage. Organic matter and clay particles form chemical unions that cause the soil to form into clumps or aggregates. These aggregates allow water to flow more easily through the soil and make it easier for roots to penetrate.