Preventing damping-off in seedlings
It is a frustrating sight: the sowing has just come up, the seedlings stand fresh and green – and overnight they buckle at the base and fall over. This so-called damping-off is caused by soil-borne fungi such as Pythium and Rhizoctonia and occurs mainly during propagation.
Once affected, the seedlings cannot be saved. The good news: with the right propagation conditions the disease can be prevented almost entirely – it is mainly about hygiene, light and moderate watering.
In short
- Seedlings buckle just above the soil and fall over.
- The stem base is thin, dark and looks constricted.
- Cause: too wet, too warm, too dark and sown too densely.
- Prevent: low-nutrient seed compost, place bright & cool, airy, water moderately.
How to spot damping-off
The seedlings show a thin, glassy to dark-brown, constricted spot at the stem base. There they buckle and lie flat shortly afterwards. The damage often spreads in patches – within a day or two a whole seed tray collapses. The roots are brown and poorly developed.
Why it occurs
The fungi are present almost everywhere and strike when conditions favour them and disadvantage the seedlings: permanently wet compost, stagnant air, too-high temperatures combined with little light, sowing too densely, and contaminated compost, containers or watering water. Nutrient-rich compost and over-fertilising encourage the infection further.
Preventing damping-off
- Low-nutrient seed compost: use special, low-nutrient seed compost – not old, damp potting soil.
- Cleanliness: clean pots, trays and tools before sowing; use clean, room-temperature water.
- Do not sow too densely: airy spacing so the surface can dry off.
- Bright and not too warm: after germination, place cooler and very bright – little light with much warmth encourages spindly, susceptible seedlings.
- Water moderately: keep the compost only slightly moist, ideally water from below and pour off excess water; avoid waterlogging.
- Ventilate: air covers daily so no stagnant, humid air builds up.
- Dry the surface: a thin layer of sand or vermiculite on the compost keeps the neck of the root drier.
What to do in case of infestation
- Remove affected seedlings immediately together with the surrounding compost.
- Place drier and airier: reduce watering, take off the cover, provide light.
- Chamomile or horsetail tea: sprayed preventively over the sowing they have a mild strengthening/germ-inhibiting effect.
- Start over: in case of severe infestation, repeat the sowing in fresh compost and clean containers.
Tip
Less is more with watering: most losses in propagation are caused by conditions that are too wet, too warm and too dark – bright, cool and moderately moist is the recipe for strong seedlings.
Caution
Do not use already-used, damp compost from the previous year for propagation – the pathogens are often already present in it.
Frequently asked questions
Can I save collapsed seedlings?
No, once buckled seedlings do not recover. Remove them to protect their neighbours.
Do I have to sterilise seed compost?
Fresh, low-nutrient seed compost is usually enough. Hygiene, light and moderate watering matter more.
If your own propagation feels too tricky: our strong, already well-rooted young plants save you the delicate germination phase.