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:

open lotus garden seedlings

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.

open lotus garden soil sterilizationA 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.


About Ashley in Open Lotus Garden

Organic and biodynamic gardener, writer/editor, lover of nature, animals, and the world.
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47 Responses to Seed Starting – Avoid Damping Off by Cooking Your Starter Mix

  1. Thanks for this post! My mother’s green thumb failed to rub off on me and this explanation about starting seeds was really helpful. Maybe failing to take the steps you’ve described is why I’m still staring at empty pots of soil. Will try your tips out over the weekend. Thanks 🙂

    • I struggled to start seeds for quite awhile before I realized that damping off was the main problem. Now that I know how to deal with it, I’m a green thumb extraordinaire! You may have a green thumb, after all, too! 🙂

  2. Great post. Good luck with this year’s garden!

  3. What an amazing tip — I never thought about “cooking” the soil. Awesome…


  4. Harold says:

    Thanks for the tips and congrats on being FP!

  5. z ... says:


    Very interestin
    Thank you


  6. ournote2self says:

    Thanks for the great ideas! Good luck with your garden.

  7. P'funk says:

    Interesting. I have heard of cooking soil before, especially to remove weed seeds etc. I have been starting plants indoors for three years now and have never had a plant damp off yet. It may be because we have forced air gas heat, up north here, and the inside air is very dry while we are starting plants. I had never really thought about why before. I start tomatos, kale, and sunberry inside. I usually fail to remember to punch drain holes in the bottom of cups that I use, so I water sparingly, not until there is a slight sign of wilt in the leaves. I still have not had damp off even though I know it is a primary cause of loss. It must be that super dry gas heated air we live in!

    • Yes, one of the added benefits of cooking the soil is that you won’t get any unexpected “volunteer” seedlings. We have a LOT of them usually, because our seed starting mix is mostly made of our kitchen scraps, which have been composted in our worm bin. A little time in the oven takes care of that, though.

  8. Josh says:

    thanks for the info!! i gonna try also

    free training

  9. Very timely post for me! My seedlings are roughly the size of what you have pictured. The lettuce, which is new to me, is confusing me b/c it doesn’t seem to need as much water as the other veggies I have going. Now I know to pay close attention to that!

    Thanks, and congrats on being Freshly Pressed. 🙂

  10. Great advice! I am going to forward to my brother who is starting seeds indoors for the first time this year. I have heard of doing this before, and I think I have help my grandma do this when I was little. The chamomille/garlic is a wonderful tip for everyone b/c it can inhibit fungus anywhere, anytime, with plants of other things too!
    Good pick for Freshly Pressed! Congrats!

  11. Thanks for posting about this- I have just planted herbs… on windowsill boxes but hey- we all gotta start somewhere….

  12. Thank you so much for this article!! I had a garden tragedy last year and was feeling a little worried about this year. The perfect post, at the perfect time. I owe you one!

  13. CrystalSpins says:

    I’m totally forwarding this to my mom. She has already started her seeds for this year, but she had a few boo boos with them. I know she didn’t cook her soil. So, maybe next year! Thanks.


  14. Phil says:

    Thanks. Maybe I’ll have some good plant seedlings this year.

  15. Cool! I have absolutely no talent with plants but I’m trying to learn… I’ve just found out about a local woman who grows her own organic fruit and veg and raises chickens and all sorts of fun stuff that sounds amazing, so I’m hoping to be able to go out to her place and learn some things hands-on, but reading posts like this certainly helps too. 🙂

  16. My green thumb just got a whole less green! Thank you. Congrats on Freshly Pressed it’s well deserved.

  17. Thank you so much. I just lost nearly all my tomato seedlings to damping off. Next time I’ll be able to prevent it.

  18. Editor001 says:

    What a fantastic idea. Thanks for the garden tips. I’m off to pick up a truck load of worm castings!

  19. beckyspringer says:

    I might try this. I was planning on starting my garden this weekend, but when I woke up to FROST on the ground this morning i thought better of it. Thanks for sharing!!

  20. Well, now I know what happened with my herb starters. Things started getting better once I started allowing some air source. At least it did for the cilantro and sweet majoram. The basil and parsley, not so much.
    Congrats on being pressed!

  21. Ascentive says:

    I just lost a bunch of swiss chard that I had started several weeks ago. I’m starting over… I’ll have to try your ideas…

  22. rtcrita says:

    I might just have to try this. I don’t have much luck with starting seeds inside. I don’t do well with houseplants either. But outside…I can keep things alive and help them grow! I always start my seeds directly outside in the ground because I always figure if they are hardy enough to get started outside and make it through our rainy, windy springs we sometimes have (including many tornadoes), then they will surely make it through the summer and produce well. It’s like survival of the fittest out there in my backyard. 🙂
    Good tips!

  23. morgaineotm says:

    This is great advice and thanks for sharing. Thankfully, have not really had much of a problem with damping off. And you would not believe the abuse my seedlings take! maybe its because they are in a big greenhouse with lots of air circulation. By the time they are up and out of the ground I’m usually watering with a rain nozzle on the hose! This year, has been a really good one with strong healthy seedlings already being set in the garden with wall-o-waters!

  24. Srulz says:

    I can learn from your post …
    thanks .. 😉

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  26. Thanks for the tip. My husband and I started growing our own plants (peppers, tomatoes, herbs etc) from seeds in our mini greenhouse. (We got the seeds from vegetables we had grown in our garden a year earlier.) They are shooting up quite fast, and so far haven’t wilted. We are waiting for the weather to get drier and warmer, so we transplant them outdoors. We’re hoping that the shock of going from the greenhouse to the “real world” is not going to effect them too much! :0

    • They should do fine! Peppers and tomatoes in particular love heat and sun, but they’ll benefit from being “hardened off” to make the transition from inside to outside with minimal shock. Basically, it’s weaning them off being pampered…letting them get gradually acclimated to more sun, more heat, and less water, a few hours at a time.

  27. Jeremy says:

    Thanks very much! My landlords garden often and all that is left of their seedlings is eggplants and Indian eggplants, I shall pass this on to them. Thanks again!

  28. shanegenziuk says:

    That is an interesting approach I had not even considered. Will give that a try for my next seedling batch, and will go for a healthy dose of my worm tea.

  29. Great advice with a simple solution!
    I lost last year’s lettuces to this – so I’ll have to try it this year.

  30. very informative to all of us who have a passion for plants. thanks.

  31. amcalonder says:

    Glad I came across your blog on the WordPress homepage– the Open Lotus Garden sounds like a great initiative and you guys have a ton of great ideas. Normally I would assume the idea of cooking soil to be more destructive than beneficial, but it seems you’ve figured out how to compensate. I’ll be looking forward to the compost tea and anti-fungal preps!

    • Thanks so much! I’m so lucky to be getting that exposure and being able to connect with folks who I can share with. I’ll post the compost tea how-to and anti-fungal preps really soon, so stay in touch! 🙂

  32. l0ve0utl0ud says:

    Thank you very much for the advice. This is my first year of gardening (on my balcony!) – I have basil, thyme, rosemary, mint, lavender, strawberries and various flowers, so all advice is extremely useful to me.

  33. Heather says:

    Thanks for the great tip! This is my first try at starting seed inside and I’ll be sure to cook the soil. Also, I loved the video on the Sharing Garden, what a wonderful idea!

  34. JavaLoco says:

    organic food,.. it’s always healthy and delicious.

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  36. Ross Mapson says:

    Is it true that if the dirt is heated to over 180 degrees Fahrenheit toxins are produced that will kill the seeds so they will not germinate.

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