Damping-Off Symptoms, Treatment, and Prevention

Damping-off is one of the most common reasons for seedling failure. This fatal disease causes seeds to decay before germinating, or the seedlings to rot, keeling at the soil line where the fungus attacks the stem. Today we will take a deep dive as to what damping-off really is, symptoms to look out for, how to prevent it, and tips on how to kill the deadly fungus!

What is Damping-Off?

Damping-off is a common disease that causes seeds to rot and can destroy seedlings as a result of soil-borne fungi; common fungi include Pythium spp., Rhizoctonia solani and . These fungi can live in soil or on soil-contaminated items (e.g., pots, trays, workbenches), thriving in wet and cold conditions. Once seedlings are infected with these pathogens, it can be difficult for the seedlings to grow into robust plants. It is more common to see damping-off in seedlings that have been started indoors than outdoors.

seeding with damping-off

How the Pathogens Work

These soil-borne pathogens produce several types of spores that can be passed through infested soil or plant material. Sporangia (which are the sacs where spores are produced) can infect plants directly or produce motile spores, known as zoospores, which allow the fungus to spread in saturated soils or standing water. Oospores are thick-walled spores, which allow the fungus to survive on equipment or in soils for long period of time. These spores are the reason why we suggest disinfecting and cleaning stations and reusable cells or trays before and after usage! Like all living things, their goal is to survive, making this disease highly contagious.

Symptoms to Look Out For

Some early symptoms of damping-off include seedlings that have failed to emerge from the soil, or first leaves (cotyledons) that are wilted, soft, or discolored. It is also common to see a white fungus that looks almost fluffy growing at the soil line. Growth will be stunted as the roots will be weak or absent. Infected seedlings will become thin where the fungus is growing and may even look like they've been pinched and turn brown.

The period between germination until the plant is able to grow its first set of true leaves is when seedlings are most susceptible to damping-off pathogens; special care and considerations should be taken. Plants with established roots and mature leaves are better able to resist the fungus or mold that causes damping-off.

Preventing Damping-Off

  • Use a seed starting medium and pots that ensure good drainage of excess water.
  • Sterilize pots, trays, tools, and supplies before and after use, and use sterile seed-starting mediums. Sanitize with a bleach solution, vinegar solution, or hydrogen peroxide.
  • Keep hoses and water heads off the floor.
  • Keep a clean workspace.
  • Use a fan to provide efficient air circulation.
  • A heating mat will help avoid cold, wet conditions where damping-off fungus thrives.
  • Use lukewarm water to water young seedlings, as cool temperatures slow plant growth and increases the opportunity for infection.
  • Provide 12-16 hours of soft white light to ensure strong and healthy seedlings.
  • Do not apply fertilizer until several true leaves have developed. After the seedlings first true leaves have emerged, you may transplant them into a container with fertile soil which won't require fertilizer until the plant is 3"—4" tall.
  • A greenhouse or soil thermometer will help you keep a closer eye on the growing conditions.

Damping-off pathogens thrive in cool, wet conditions. Therefore, any conditions that slow plant growth will increase the opportunity for infection. This includes low light, overwatering, high salts from fertilizer, and cool soil temperatures.


Cinnamon is an anti-fungal and kills fungi spores like the ones that cause damping-off. Dusting cinnamon on your soil surface will prevent and treat the damping-off fungus from killing your seedlings. You may even make a cinnamon tisane by pouring warm water over some cinnamon and steeping overnight, and spraying the stems of the infected seedlings or bottom watering with this solution. This treatment has been debated by gardeners for years. Try it for yourself, and see if cinnamon can save your seedlings!

Written by Madeleine Pesso

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