Prevent problems in seed starting soil

Growing your own transplants from seeds is a very satisfying experience which can save you money, too. However, it is not without its problems.

Just about every gardener who has started plants from seed has a story to tell of watching a crop of seedlings that were just starting to make good growth, then all of a sudden, the plants shrivel at the soil line, fall over and finally die.

That is a symptom of a condition known as "damping off." Early in my horticulture career I heard some old timers refer to it as “wire stem.”

Damping off also kills newly sprouting seeds under the soil, giving the impression of a low germination rate. As a result, the gardener gets the wrong impression that he's planted a batch of bad seed when in reality it's damping off.

Other symptoms may include wilting leaves, mushy spots on leaves or fine cobweb-looking mold filaments on or around the plants.

Damping off is most commonly caused by a soil based fungus called Phythium, but Rhyzoctonia and other species of fungi can cause it as well. Once a plant is infected, the disease is not curable no matter which species of fungus is causing the problem.

It's an insidious disorder. The seedlings can look sturdy and strong on day then suddenly, bam! overnight an entire tray of seedlings becomes infected. There is no cure for damping off, affected plants always die.

Most of the time you can avoid damping off by purchasing a fresh bag of sterilized soil-less seed starting mix. Sometimes however, even a new bag of starting mix can harbor fungi, although that is pretty rare.

When these fungal diseases show up, it's probably the gardener who contaminated their seed starting mix by using dirty tools, pots, or even the potting bench.

All planting tools and containers need to be scrubbed clean with a detergent. Mix up a solution of one part chlorine bleach to nine parts water to get a 10 percent solution. Then place your items into the solution and soak for 30 minutes. Afterward, rinse well and allow to dry before using.

Although all plants can be infected, some species of plants are more susceptible to damping off than others. For example, petunias are very susceptible to the infection.

Since damping off is more likely to start in compacted soil, resist the temptation to press down your seed starting mix when filling your containers or placing your seed. Instead leave the soil fluffy.

Growing seedlings in a cool environment also makes it more likely damping off will happen, so keep your seedlings warm. That being said, even though it is less likely, some fungi can cause damping off even in warm, dryish growing environments. That happens only in a small percentage of cases.

There is a way to make sure your starting mix is free from pathogens. Whenever I start a batch of expensive or hard-to-find seeds and don't want to take any chances of losing those precious seedlings, I take the extra step of re-sterilizing my starting mix. Some might say I'm being extra cautious, but sometimes seeds are irreplaceable and need all the protection we can give them.

For small amounts of soil, I pour boiling water through a pot of starting mix — then go back and do two additional pours. If you decide to try it yourself, be sure to place the pot in a spot where the water can drain through easily. I like to do this outside on a wire rack rather than in the sink.

This boiling water method has been used by gardeners for generations and has shown to be pretty effective. Since the entire volume of the soil mix will not reach 212 degrees Fahrenheit — the temperature at which it would be considered sterile — this hot water method could be considered more of a pasteurization method rather than actual sterilization technique. It still adds one more layer of protection though.

I’ll be starting my cabbage, broccoli, Brussels sprouts, peppers and agastache soon. Outdoor spring planting is getting closer.