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Preventing damping off of seedlings

Garden Chat
For healthy seedlings and to prevent damping off from shattering your spring joy, supply good light, lots of room, even moisture and warm soil.

You’re excited for spring to arrive. And you’re a DIYer. So you start seeds now instead of buying transplants in May to save some money and to have more choice of plants and varieties. What could be simpler? Put soil in a pot, plant some seed, cover with more soil and add water. Then wait for the miracle of germination. But then shortly after the seeds sprout, they all fall over. Dead. The promise of spring joy is crushed. What happened? Damping off happened. 

Damping off is a disease caused by one of several different soil fungal organisms. Specific symptoms vary depending on the fungus, but essentially, emerging seedlings are attacked at or below the soil surface causing them to keel over. 

Damping off fungi are found naturally everywhere in the environment – living in soil and on decaying plant material, and they can be spread by water and in the air. Fungal spores can even survive dormant on the seed itself, waiting for ideal conditions to come alive. One thing many of the damping off fungi have in common is their ideal growing conditions: cool, dark and wet.

There is no cure, only prevention. Prevention starts with using clean containers and tools. If you’ve had damping off problems in the past, start with new containers. If reusing containers, scrub debris off with soap and water or run through the dishwasher. Then soak them in a weak bleach (100 millilitres per litre of water) or hydrogen peroxide (10 millilitres of three per cent per litre of water) solution for 20 minutes, rinse then air dry. 

Use sterile seedling mix. Do not use anything that contains garden soil. First, it is a potential source of damping off fungi (as is garden compost). Second, it holds on to too much water when in pots, creating an ideal environment for fungal development.

Vigorous seedlings are less susceptible to damping off, so fresh seed is best. Warm conditions will accelerate seedling growth and development, putting them past the susceptible stage quickly. Use bottom heat (with seedling heating pads) and shallow containers to speed this process up. Bright light will prevent weak, spindly seedlings from developing. Also, give seedlings lots of room. This may mean removing or thinning out excess number to give the remaining seedlings access to sufficient light, space and water to maximize growth rate. This also reduces the relative humidity surrounding the plants, reducing the optimal environmental conditions for fungal development. 

Maintain even soil moisture – never too wet nor too dry. Water from below by soaking pot/seedling tray in a shallow container filled with water for 15 minutes. Remove and allow pots to drain completely. Water only when the top surface is dry to the touch. If using a cover to maintain high humidity conditions for small, shallow-planted seed, remove shortly after seedling emergence.

There are no registered fungicides to control damping off for home gardeners. There are a few home remedies you can try but this author offers no guarantees: 

After seeding, sprinkle the surface with a thin layer of coarse sand or small grit.

Apply a one-time dusting of cinnamon or charcoal dust after seeding.

Water with a mild chamomile tea solution (30 – 60 millilitres of strong tea per litre of water) and/or spray on the soil surface.

Water with a mild hydrogen peroxide solution (15 millilitres of three per cent per litre water).

— This column is provided courtesy of the Saskatchewan Perennial Society (;; NEW Check out our Bulletin Board or Calendar for upcoming garden information sessions, workshops and tours. Visit our booth at Gardenscapes – the Backyard Lifestyle Show, April 8-10 at Prairieland Exhibition, Saskatoon.