Why Do My Thyme Plants Turn Brown in the Center?

Disease

• The most common reason that thyme plants turn brown is a fungal disease. Root rot diseases or rust can infect thyme, causing the leaves or entire root system to turn brown or black. Leaves and stems may shrivel and die or become mushy.

Causes

• Thyme is a Mediterranean herb that thrives in full sun and warm, mild temperatures. Shaded, crowded conditions may make the plant more susceptible to disease. Poorly draining soil is often to blame for root rot diseases. Fungal diseases may live on in soil, causing future infections.

Prevention

• Plant thyme in well-draining, slightly sandy soil, and space plants at least 12 to 18 inches apart. Plant thyme in a sunny, hot area. Do not reuse potting soil if plants from the previous year exhibited signs of disease, but start with fresh potting soil for container-grown thyme. Allow the soil to dry out somewhat between waterings. Thyme is fairly drought tolerant, and overwatering contributes to disease and dilutes the essential oils of the herb.

Cures

• If the roots are brown or black, the plant probably can't be saved. Discard it before it infects other plants. Cut the plant back to ground level if only the leaves are infected, and scorch the crown and surrounding soil with a flame gun. The plant will eventually regrow, but burning it slightly kills the disease so new growth is healthy. A commercial fungicide may also control minor fungal diseases that cause brown leaves. Replant thyme in well-draining soil if the soil is heavy and wet.