How to Prevent Damping Off in Seedlings

Have you found that your seedlings germinate perfectly, start to grow, and then some days or weeks later they go “limp”? Seedlings suffering from the disease known as “damping off” typically develop weaknesses in their stems, which start to look thin in places, before they bend over at the weakness and slowly die.

Sadly, once a seedling has been affected there is typically not much that can be done to save them – but there are things that will prevent such a situation occurring again in the future.


What is Damping Off?

Damping off is a microbial infection that can affect seedlings. The micro-organisms get into the cells of the seedling causing irreparable damage. Seedlings typically won’t die overnight, but instead will spend some days or even weeks “fading” from glory, with the obvious “pinch point” on their stems.

What Causes Damping Off?

Damping off tends to occur most commonly in very damp environments. A common example is seeds planted very early in the year in a greenhouse or cloche. In early spring rainfall can be considerable. Within the enclosed environment of a greenhouse the moisture just sits around, allowing the infection to take hold.

Sadly, damping off can spread quite quickly under such circumstances. It is not unusual to have one small pot of seedlings affected, only to find some days later that a range of containers in your greenhouse are affected, and that seedlings seem to be keeling over and dying all over.

Are Some Plants More Affected Than Others?

While there are no scientific studies I am aware of, it seems that all seedlings are affected equally by the risks of damping off. However, the problem tends to only occur in very small seedlings. It seems that larger plants can fight off the attack far more effectively. The first month or so after a seed germinates is really the danger area.

How to Prevent Damping Off

There are three core tactics which can help you to prevent damping off…

a) Suitable Aeration

First and foremost you want to prevent an atmosphere that is too moist, especially when the environment is also reasonably cool. For this reason, if you’ve been affected in the past, it can be a good idea to remove the lids of propagators once seeds germinate, to consider leaving the greenhouse door open in better weather, or even to consider installing a small fan to improve air movement.

Your goal should be to avoid stagnant, stale, damp air from sitting around your plants.

b) Moderate Watering

Secondly, heavy watering can also have a significant impact on the prevalence of damping off. Don’t put pots of seedlings in trays and water heavily. Instead, water moderately, and allow the compost to dry out gently between watering. This cycle of moisture in the compost can be very effective for reducing the incidence of damping off.

c) Careful Sterilization

Lastly, be aware that the micro-organisms which cause damping off can easily be transferred from sick seedlings to otherwise healthy ones.

If you’re unfortunate enough to be affected by damping off then you want to dispose of those seedlings as soon as possible – don’t hold off in the hope that they’ll recover. Furthermore, don’t re-use their compost, and be sure to carefully sterilize the plant pots too (hot water from the kettle tends to work well).

In short, as soon as a problem occurs, and you see those thin and/or drooping stems its time to get rid of the infection before other seedlings are affected.

Follow these simple steps and you should find that the problems of damping off become a thing of the past.

Do your seedlings die soon after germinating? If so they could be suffering from damping off. This article discusses how to avoid or treat the problem when you're sowing new seeds in your greenhouse or garden.