How to - Seeds

How to prevent damping off

Protect your precious seedlings with these green thumb tips.

After the exhilaration of seeing your seedling poke its way through the soil, there is nothing more disappointing than having it suddenly topple over and wither away.

Damping off—a condition where a seemingly healthy seedling suddenly dies—is the result of a fungus attack. Invisible to the eye until too late, the condition is usually fatal, but one that is easily preventable.

Funky fungi
At any given time there are a number of fungi lurking in our soils, waiting for just the right conditions to bloom. There are many different types of fungi that can cause damping off, but the three most common ones are Rhizoctonia solani, Pythium spp and Fusarium solani. While each is different, they all thrive in overly moist conditions.

Rhizoctonia solani: Found in all natural soils, it springs to life when the soil is moist and hot. The infected seedling will have a sunken lesion on its stem where it touches the soil or just below the soil line.

Pythium spp: Thrives in cool, overwatered and poorly-drained soils. It produces a damp, odourless rot that causes the outer portion of the root to become slimy. In severe cases, the lower portion of the stem may appear slimy and black. Pythium can survive in soil for several years.

Fusarium solani: Remains inactive for long periods of time, favouring acidic, coarse and poorly fertilized soils. Infected seeds usually fail to germinate and become soft and mushy, eventually disintegrating. Dark and moist lesions on the stems may also appear with "wire stem," where the stem becomes much thinner above the lesion. The lesion gradually grows until the seedling dies.

Give your seeds a clean start
It's easy to transfer fungal infections using unsterilized outdoor gardening tools or dirty pots. Before planting, sterilize both using a weak hydrogen solution: 10 ml of hydrogen peroxide to one litre of water. Leave the solution on for five minutes, rinse off and air-dry.


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