Seed Starting – Avoid Damping Off by Cooking Your Starter Mix

Early to mid spring is a very busy season, because it’s the time that we start almost all of  the garden vegetables, fruits, and herbs from seed.  Below are some of my seedlings from this year.  From left to right, you can see the clary sage, dill, lettuce, a row of mixed “volunteers,” New Zealand spinach, and lacinato kale:

One of the common problems that gardeners may run into when starting their plants from seed is the dreaded, heartbreaking damping off:  Your seedlings might be doing beautifully for days or even for weeks, but then they start to lose vigor and within days they’ve wilted beyond resuscitation—the stems have wasted away to nothing where they meet the soil, and you have to start all over, if you hope to ever have a happy garden. It’s pure, unmitigated garden tragedy.

Believe me, I’ve lost more than my fair share of plants to damping off.  This malady happens when warm, most conditions (the type of conditions that are beneficial to germinate most seeds) also prove to be sufficiently beneficial to any variety of fungi residing in the seed starting mix.  They then essentially choke the baby plants by grabbing them around the throats.

There are a few things you can do to prevent this.  First is keeping the soil a bit drier, and employing bottom-watering (through capillary action) rather than watering from the top.  Another thing you can do is ensure that the seed starts are getting adequate ventilation.  If you have a lid or a dome over them, make sure there are some openings so that air can circulate in and out, and that it doesn’t get too humid in there.

However, even these precautionary measures don’t guarantee damping off won’t occur, so I’m trying some different techniques this year.  First, I’m sterilizing the starter mix that I use (which is screened compost from the garden, mixed with a bit of coir and vermiculite).

Now normally, a healthy variety of mirco-organic life in the soil is really, really important for growing healthy plants.  However, while plants are just seedlings, they’re more vulnerable to fungus, and so this is where I’m going to make the only exception to my  rule of cultivating diverse soil flora.

Soil can easily be sterilized by putting it into a pot or dish, and simply popping it into the oven.  Getting the soil temperature somewhere above 200 degrees for 5 minutes or so should do the trick.

A word of warning:  This is a bit of a smelly process.  Since the soil is full of all kinds of bacterial and fungal life, when it gets heated up, the smell is pretty intense.  It’s still totally worth the effort, but it’s a good idea to do it on a nice day when you can open up the windows and maybe step outside into the garden for a few minutes while the stuff cooks.  (I’ve also heard of people doing this in the microwave.)

In order to compensate for the sterility of the soil, which pampers the seedlings and doesn’t encourage them to grow strong and tough, I’m spraying them regularly with compost tea  (which is rich in beneficial bacteria) and also with a chamomile/garlic preparation, as both garlic and chamomile have natural anti-fungal properties and won’t harm the seedlings.  I’ll be writing a post that will show you how to make your own compost tea and anti-fungal preps soon!

Happy seed starting!

Have a question?  Just post in the comments section below and I’ll see what I can do to be of help.