Damping off is a disease that affects house plants, greenhouse plants and garden flowers.

It is a soil-borne fungus capable of “damping off” seedlings, roots and crown (foot) rots of plants.

The fungus kills both germinating seeds and young seedlings.

Entire seed flats of house plants, bedding annuals and perennials are often lost to damping off.

Pre-emergence damping off is the term used to describe the rot of seeds or death of the seedlings before they emerge from the soil.

Post-emergence damping off affects seedlings that have already emerged from the soil.

These seedlings may develop a dark stem rot near the soil surface, which will cause them to fall over and die as the rotted area shrivels.

They may also rot from the tip of the roots. This rot progresses from the roots up to the seedlings until the stem is rotted.

Seedlings that survive before they get infected may develop “wire-stem,” a condition in which the base of the stem is partially invaded by the fungus.

There is often a discolored and slightly shriveled or constricted area at or just below the soil line.

The most common root-rotting fungi are Rhizoctonia solani, species of Pythium and Phytophthora, and Thielaviopsis basicola. Others include, Sclerotinia sclerotiorum, Sclerotium rolfsii, Macrophomina phaseoli, species of Botrytis, and species of Aphanomyces, Fusarium, Cylindrocladium.


Here are some typical characteristics of the different varieties:

  1. Rhizoctonia solani damping off breeds reddish brown lesions on the stem at the soil line and may girdle the stem in warm to cool soils.
  2. Pythium damping off collapses the stem at the soil line or below the soil surface and results in black, rotted roots on older seedlings; this usually occurs in warm, wet soils.
  3. Thielaviopsis basicola damping off produces black root rot of seedlings. Plants may grow out of the disease but they remain stunted compared to healthy plants; usually in cool soils.
How to prevent damping off

There are many ways to prevent damping off. It is most effective to use a combination of techniques.

First, keep the fungus out of flats of seeds by:

  • Planting seeds and root cuttings only in sterilized seedling mix or other planting material and only use sterilized containers.
  • Use clean, non-recycled water on the seeds.
  • Place seed trays on clean, sterilized benches.
  • Restrict soiled hands and tools that come in contact with the sterile media.
  • Immediately remove any trays with signs of damping off.
Second, encourage seeds to germinate and grow as fast as possible by:
  • Using adequate light and heat to germinate and grow seedlings quickly.
  • Bottom heating to speed germination.
  • Avoid planting seeds too deeply.
Third, maintain conditions in the seeding trays less favorable to the fungi by:
  • Using well-drained planting media.
  • Sowing seeds thinly to allow air to circulate between seedlings.
  • Avoid excessive watering.
In addition to these measures, using fungicide-treated seeds goes a long way in preventing damping off.

Got more ideas for how to prevent or treat damping off? Let us know in the comments below.

More info:

University of Connecticut page on Damping Off

University of Arizona Cooperative Extension page on Damping Off (PDF)

University of Illinois Extension page on Damping Off (PDF)

See also:

What is pythium?

What is phytophthora?

Tomato diseases