HOW TO PROTECT SEEDLINGS FROM DAMPING-OFF
Probably a lot of backyard gardeners by now have put seeds in pots, trays or some other kind of container. After anxiously waiting for the little sprouts to poke out of the soil, they are excited to see the first two leaves open, the cotyledons. The gardeners provide a little more water and maybe rotate the trays so that the new sprouts share the light. Like the gardeners, the new sprouts must be happy. What could possibly go wrong?
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| Damping-off. Source: Cornell University |
There's actually a lot, but most probably a gardener will go down into their cellar or out onto an unheated sunroom one morning to check on the seedlings and find them sprawled over with their stems looking pinched and maybe their leaves starting to look discolored. Pulling up one of the shoots the gardener notices that its roots have not developed very much. What happened?
Looks like damping-off (or damp-off) to me.
Damp-off is typically caused either by one of two fungi: Fusarium spp. and Rhizoctonia spp. or by a Pythium spp. ["spp" stands for subspecies]. The latter is a water mold and is recognizably distinctive because of its tiny white filaments. A microbiologist would say that it's distinguished from fungi by being diploid (i.e. having 2 sets of genetic material rather than being haploid like fungi with only 1 set). The two fungi may or may not appear with some kind of obvious fuzz, but infected plants will show various discoloration, and sometimes seeds will not even emerge from the soil.
All these pathogenic critters are generally present in garden soils just waiting for the right conditions, like the ones some gardeners inadvertently provide, to spring into action. The pathogens do not normally have much impact on maturer plants, but they can. For example, the Irish Potato Famine was caused by a water mold (Phytophthora infestans). It commonly shows up at the end of summer or during autumn as "late blight" when the weather turns cool and wet.
Gardeners may not care much about whether a fungi or a water mold did in their tomato seedlings, but they do need to know how to avoid the conditions that trigger "damp-off." The peppers in the pot of the first photo either were not in a sterile pot or in sterile garden soil, perhaps both. The second photo shows the result of someone in a hurry to get seed in the ground and not waiting until the soil was a little drier and/or and a little warmer, On the other hand, maybe that gardener was just unlucky and hit a really bad streak of spring weather. Obviously, gardeners cannot control the weather, but here's what they can do next time to reduce the risk of pathogens from winning.
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| Damp-off in early spring garden. |
All these pathogenic critters are generally present in garden soils just waiting for the right conditions, like the ones some gardeners inadvertently provide, to spring into action. The pathogens do not normally have much impact on maturer plants, but they can. For example, the Irish Potato Famine was caused by a water mold (Phytophthora infestans). It commonly shows up at the end of summer or during autumn as "late blight" when the weather turns cool and wet.
Gardeners may not care much about whether a fungi or a water mold did in their tomato seedlings, but they do need to know how to avoid the conditions that trigger "damp-off." The peppers in the pot of the first photo either were not in a sterile pot or in sterile garden soil, perhaps both. The second photo shows the result of someone in a hurry to get seed in the ground and not waiting until the soil was a little drier and/or and a little warmer, On the other hand, maybe that gardener was just unlucky and hit a really bad streak of spring weather. Obviously, gardeners cannot control the weather, but here's what they can do next time to reduce the risk of pathogens from winning.
- Clean gardening tools and wash your hands before handling seeds or seedlings if you have been handling unwashed tools, pots and other containers.
- Use a heat mat under your tray or pots to keep soil temperature in the low 70s° F.
- Invest in sterile starter or planting soil. Don't use soil from the garden.
- Wash and sterilize trays and pots before use. Soak'em in a 10% solution of household bleach.
- Don't overwater and make sure pots and other containers have drainage holes. Seedlings like to be moist, but not drowned.
- When watering, use warm tap water to promote root growth. Roots do not enjoy cold baths.
- After the first 2 - 4 true leaves develop (not the very first 2 leaves, the cotyledons), recheck the potting mix's label because many starter mixes contain slow release fertilizers at the right strength. If they do, don't fertilize. If you have to add fertilizer, then add it at no more than 1/4 strength.
- Look for excessive condensation on the inside tray or container covers. If moisture is dripping down, remove the covers, shake off the condensation and allow for more air flow.
- Provide 12-14 hours of light each day from either a soft white fluorescent bulb or a grow light.
Remember that you are creating a nursery for young plants, and the seedlings will benefit from whatever head start you take care to provide...
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