How To Prevent Damping Off and Dead Seedlings

If your seedling suddenly keels over and dies — it’s likely damping off.

Doug Green
Oct 31 · 4 min read

Damping off is a stem rot problem where a seedling will suddenly keel over and die or the seed will germinate and never develop.

It occurs in most soils — both in the garden and in the greenhouse if the right conditions exist.

Cool Wet

In general, cool wet soils support the development of the damping off fungus (rhizoctonia) and seedlings either die in the seedling flat or die upon transplanting.

I note that I’ve never seen older, established plants attacked by this problem but I’m told it can happen.

Older plants develop a secondary stem tissue that forms a protective barrier and stops the fungus from penetrating the stem. Having said that, the fungus will still attack roots and parts of the stem of a weak plant in cold, damp soils causing a sub-standard seedling or plant.

Identifying Damping Off

How do you know you have damping off?

Generally, infected plants keel over and die. You may see some water-soaked looking spots in the stem and when the plant falls over you’ll see the stem rotting away below the collapsed area. Or, more likely the stem is attacked right at the soil line and all you can see is a fallen over seedling.

Seeds simply don’t germinate and while this can be blamed on a wide variety of symptoms, cool damp soils and damping off are most often the cause of indoor seed problems. I can’t recommend a small soil heating mat too strongly. I use one and couldn’t imagine starting plants without one.

Preventing This Problem In Your Seed Starting Area

Given that poor growing conditions are the primary cause of this problem, the first “cure” is to fix those poor growing conditions.

  • Increase the temperature of the soil to 70F using heating growth mats
  • Decrease the watering so the soil is uniformly damp but not swamped. Always use lukewarm water when watering seedlings.
  • Thin seedlings out. Poor air circulation increases the likelihood that fungus will survive.
  • Ventilate the seedling trays. Again, poor air circulation is simply asking for a fungus to start growing. In our nursery propagation greenhouse, I always had fans gently blowing on top of the seedling trays to keep an airflow over the top of the germinating seeds. I want the soil to be “just damp” but the seedlings to be dry.
  • Avoid frequent waterings of seedling trays. The seedlings will be fine if the soil is damp — they don’t require swamps. Water thoroughly and then allow the tray to dry out a bit until you can barely feel it is damp. Then soak it again.
  • Always use sterilized soils for seed starting. Never use soil straight from the garden or soil that has been sitting in the open bag for a long time without sterilizing it. The easiest way to sterilize it is to put the pot of soil in the sink and *slowly* pour a kettle of boiling water into the pot. Get the water rolling out the bottom and empty the entire kettle. Cook that soil.
  • Keep your tools clean. If you have old soil on your garden tools or old pots, then you’re asking to contaminate any soil they come in contact with. Clean old pots thoroughly and don’t grow anything in them for several months before sowing. 9 parts of chlorine bleach to 1 part of water will sterilize tools and pots nicely. Just understand all dirt has to be removed from the surface before sterilizing.
  • Make sure there’s air circulation in the area where you’re growing your seeds.

Here’s A Homemade Recipe That Might Help

Relax. Help is only a minute away without having to use some potent chemical.

  • Get a few cloves of garlic. Mash them up.
  • Put the mashed garlic and remnants into a saucepan with an inch or two of water.
  • Simmer for 15–30 minutes to get the garlic oil into the water.
  • Cool the water.
  • Pour the lukewarm mixture over the seedling flat and the damping off is history.

I note that some garden writers tell you to strain this mix and then use a sprayer. This works well if you really strain the mix well. If you don’t strain, or do a bad job of it — you’ll block up your sprayer.

I find it is easier to pour the mix into a watering can and simply water the seed flat.

Garlic is a potent fungal and bacterial killer.
But you have to change your growing habits or you’ll have the problem again. Damping off is primarily a problem caused by poor gardening conditions. Fix ‘em!

Check out the other garden solutions on my Amazon ebook list here.

(Note I get a small affiliate payment when you buy my ebooks or use links on this site.)

Doug Green

Written by

Former nurseryman, now writer and curious about what’s over the next hill and how to get there in either my Triumph Spitfire or sailboat.

Doug Greens Garden

A practical organic gardening resource helping you have a better garden

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