5 Tricks to Prevent Damping Off in Your Seedlings This Year

Damping off is nothing short of disheartening, but with a fresh start, the next round of seedlings can thrive. Gardening expert Katherine Rowe explores how to prevent the fungal disease from the get-go when seed-starting this year.

Small seedlings with rounded green leaves growing from moist soil.

Damping off leads to swift decimation of entire flats of seedlings. One day, our little sprouts are emerging, and the next, they’re toppling.

What is Damping Off?

Close-up of a seed tray with young cabbage seedlings showing signs of damping off. — Damping off often results from overwatering and soggy conditions.

Damping off is a common fungal and mold problem for seedlings. It often results from overwatering and soggy conditions, but it can impact seedlings in well-draining situations, too.

Symptoms of Damping Off

Sprouted seeds with drooping stems and fading leaves in dry soil. — Common signs include brown stems at the soil level, weakening stems, and collapsed seedlings.

Damping off happens quickly in the germination process and in young seedlings. Common signs include brown stems at the soil level, weakening stems, and collapsed seedlings.

Sterilizing Growing Containers

A yellow-gloved hand holding an orange sponge above a pink tub filled with soapy water. — Pots carried over between seasons can harbor remnants of disease-causing pathogens.

The first step to prevent damping off is to sterilize pots and other seed-growing supplies. Pots carried over between seasons can harbor remnants of disease-causing pathogens.

Bleach or Alcohol Solutions

A light blue basin being filled with water from a white bottle. — Use a bleach and water dilution (1:9) or an alcohol spray/wipe (70% isopropyl alcohol).

Two easy methods for sterilization include a bleach and water dilution (1:9) or an alcohol spray/wipe (70% isopropyl alcohol).

Start With a Fresh, Well-Draining Seed-Starting Mix

Several young sprouts with tiny green leaves breaking through dark, moist soil. — A new, sterile seed starting mix is the best foundation.

A new, sterile seed starting mix is the best foundation. Don’t reuse old potting media, as it may contain pathogens.

Drainage Test

A black seed tray with holes turned upside down placed on a pure white surface. — Good drainage is essential.

Good drainage is essential. Fill a few cells and water them in; once saturated, water should flow out of the holes rather than sitting on top.

Prevent Overwatering

Black seed tray with moist soil squares placed inside a shallow water-filled container. — Water from below to limit damp conditions on leaves.

Giving too much water is the top cause of damping off. Water from below to limit damp conditions on leaves and use lukewarm water to avoid shocking roots.

Keep Seedlings Warm

Seedlings in black trays with tender stems and small leaves placed on a windowsill. — Cool temperatures foster pathogens.

Cool temperatures foster pathogens. Aim for the ideal germination range (around 70°F/21°C) and use a heat mat if your space stays cool.

Don’t Crowd Seeds

A hand gently pulling out small seedlings with green leaves from a densely packed tray. — Cramped conditions create poor airflow, prime for fungal development.

Cramped conditions create poor airflow, prime for fungal development. Thin seedlings quickly to reduce competition and increase circulation.