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Beating the Dreaded Fungus

On my lightstand five trays held hundreds of bright-green seedlings. I was excited! Then with horror I watched the tiny stems become pinched at the soil level, and keel over.

This year, I've resolved to do it right. I began with research, including a long talk with The Seedling Specialist, Priscilla Williams of Townsend.

Rapid seed germination helps seeds get ahead of damping-off disease; seedling stems are only susceptible when very young. With many plants, bottom heat helps; you can even use a heating pad under the seed trays ... but it must be set on LOW, and removed as soon as the seeds sprout.

Priscilla uses regular organic potting soil, but warns against a high peat content. Peat retains moisture well... too well(1). Seeds need moisture to germinate, but fungus(2) thrives on it too.

Some authorities say don't cover the seed containers. But already, watering takes great care: from the bottom, and making sure the trays don't stand in water. Without covers, you'd also have to check the soil moisture every few hours! Instead, Priscilla plants only one variety of plant in each 4" x 5" flat, and covers it individually. This way, the plastic can be removed as soon as the seeds germinate, and fungus is less likely to spread from flat to flat.

Give extra light: not only so seedlings will grow, but to suppress fungus. Also increase air circulation, especially if you use lights that get hot. Priscilla uses regular fluorescent shop lights (no special wavelengths) — on chains so they can be easily raised and lowered — and a small fan.

Other strategies take advantage of the antifungal properties of certain plants. Milled sphagnum moss (not the peat form) is sometimes recommended against damping-off fungi — but it can contain a different fungus that produces serious a disease in humans, called sporotricohosis.

Before planting, inoculate the soil with a garlic infusion (1 clove garlic, pureed in a blender with 2 cups of water, steeped 24 hours and strained). With a fine sprayer, mist seedlings gently with horsetail tea, chamomile tea, or liquid seaweed. (Don't use the kind with fish emulsion in it; you don't want nitrogen, just the kelp.) And sprinkle on powdered cinnamon (no sugar).

(Note: The Seedling Specialist will probably not offer pre-order this year, but instead have one big sale, in late spring. After February 1 you can call Priscilla at (978) 597-3005, to find out.)

© Copyright 2002 Catherine Holmes Clark

Published in the six Nashoba Publishing papers on Friday, 27 December 2002
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  1. Most commonly, Rhizoctonia, Pythium or Phytophthora fungi.
  2. Peat pots get moldy easily. If you need to use them (for seedlings that dislike having their roots disturbed, like ones with taproots), try adding 1 part 3 % hydrogen peroxide (available in drugstores) to 20 parts water each time you wet your peat pots (including the first).
For more information
  • Priscilla will be teaching a class on Seed Germination on Monday, February 3, as one of a four-part series offered this spring by the Massachusetts Horticultural Society at their headquarters in Wellesley. (The other classes are Plant Anatomy and Biology, Soil, and Asexual Propagation.) For more information call (617) 933-4921.
  • "Damping Off," by Lorrie Stromme, on the Plant Health Care Update page for March, 1999, of the University of Minnesota Extension Service. — "Seedlings grown in soils that are too warm or too cold for rapid germination are more susceptible to infection. " (However she recommends chemically treated seed.)
  • Damping-off Disease, from Green Gardener Questions and Answers — recipes for a variety of natural antifungal agents.
  • Home Remedies for Fungus Gnat and Damping-Off Control, by Arzeena Hamir
  • Other biological controls for damping-off fungus:
  • Sphagnum Moss vs Peat Moss
  • Information on sporotricohosis:
  • Although Priscilla and others have had problems with peat moss encouraging fungus, there are also reports of it suppressing damping-off organisms. See Disease Suppression Associated with Sphagnum Peat Moss. This site does mention that suppression works best in the upper, "blonde" layer of peat; perhaps it's not easy getting that kind.