Garden Update | Mold in my Seed Starting Flats. Sob!

By Kiersten | Last Updated: March 25, 2014


So I have a little problem with mold in my seed starting flats. Perhaps you gathered that from the title of this post? I have the seeds in my office/craftroom and the door is closed so the cats can’t get them. And I’m pretty sure this is the issue–the air isn’t circulating. It probably doesn’t help that with the self-watering system I’m using, the soil is constantly damp, making it the perfect environment for this white, cottony mold to proliferate.

Mold in Seed Starting Flat

See the white mold on the soil?

I did a little searching and found some remedies for killing mold in plant pots. Being an organic gardener, I didn’t want to use anything too harsh. And since I’m dealing with delicate seedlings, I worried about killing them if I tried anything like that. (Some people suggested using bleach–yeah, no thanks.) So here are the steps I took to reign in this mold (at least a little bit):

  • I started by putting a fan in the room to help the air circulate.
  • I gently scraped the moldy soil from the flat and threw it out.
  • I sprinkled the whole flat with cinnamon, per a few suggestions I saw on gardening forums.
Cinnamon to Kill Mold

Mmm, smells like cinnamon!

The cinnamon seemed to work for a few days and then one morning I went to check on the seeds and the mold was back. Some seeds weren’t sprouting either, so I’m pretty sure the mold was impacting them. Out of desperation, I tried using Earth Friendly Products Cinnamon Air Freshener, since that also had cinnamon in it. And guess what? It worked!

Well, it kind of worked. The nice thing about it is that it killed the mold after I sprayed it and the seedlings didn’t appear to be harmed. (I’ve sprayed them about 5 times now and the seedlings are fine–I’m hoping this means I can continue to use it without any issues.) The bad thing is that a day or two later, the mold would start coming back. But at least I can keep it in check for now.

This isn’t the best solution, of course, and I do worry that eventually the plants will be effected by the air freshener. So I think I’m going to have to move the seed starting trays outside or at the very least, take the more established plants out of the flat and move those. I always get excited about gardening and then I remember all the problems I have growing things. Sigh.

I know a lot of you have been starting your spring seeds too. How are they doing? Have you had any issues with mold? Do you have them indoors or outside?

About Kiersten

Kiersten is the founder and editor of Oh My Veggies.

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Aw,sorry about your little green babies! Wow, mold is tricky once it gets started!
I look up to organic gardeners that don’t give up right away !
I sprinkle cinnamon on the dirt of almost every plant i grow indoors because it keeps away bugs especially gnats and any other annoying flyers. Your right…mmm cinnamon-y 🙂

hey this is what I do every year come spring. I get my flats out and get my seedlings planted.. And… Every year the same darn thing with the mold. Drives me nuts. I might just have to try your air freshener trick. Sounds like a good idea.


Please post another note after your done with this test I’d love to hear your results

Kevin 🙂

I’m new to starting plants from seed, but when I did it last summer, I did it on the porch, so I didn’t have any mold issues. I was totally unprepared for this! I think the air freshener works because it has cinnamon oil in it and a little bit of alcohol–I like it because it kills the mold on contact, so I don’t have to scrape it out. I’ve also heard that chamomile tea brewed strong will kill the mold, so you might want to try that!

I need to stop procrastinating and start my seeds!!!

I usually keep mine in the breezeway. The only airflow is when we open the door to the garage or the door to the house, so not much. I’ve had a little mold before. I usually take the seedlings and keep a little dirt on them, but repot them in another container with new soil. Used yogurt containers work very well.

Well, I might have started a wee bit early, so I think you still have time. 🙂

I repotted some of the bigger plants, but left in all the onions and leeks (which aren’t doing well–don’t want to shock them!). I’ve moved the pots to an open windowsill, so I’m hoping that will help with the mold problem.

Yay–at least one of us is having success! 🙂 The husband is heading to Lowe’s tonight, so I’m having him pick up a second grow light because I have more seeds to start next week and no more room in the Aerogarden!

Back when I had a community garden plot I used to start my own seeds. I never had a problem with mold but they got good sunshine in the window in my office (taking them to work kept my cats from devouring them). I hope yours make it to spring so you can plant them!

At least your cats eat the plants. Mine just pull them out of the dirt and spit them out! If they ate them, I’d feel like at least someone got to enjoy them, even if it wasn’t me. 😉 I moved some of the larger seedlings to the windowsill & opened the window, so I’m hoping they’ll be fine now–not so sure about the puny onion and leek seedlings that are still in the tray, though.

Yeah, I didn’t do too well last year, although it was mostly because we were in the midst of moving when I should have been starting seeds. So everything started late late late! I’m determined to do better in 2012. 🙂

Who would have guessed cinnamon did the trick! We always try to find environmentally friendly products to use, but sometimes it is really difficult. Chris’ Aunt has her masters in organic farming and I’ll ask her if she knows why the mold keeps coming back.

You know, I opened up the window in the room this week and the mold has really slowed down since then. So air circulation is definitely the big problem. Of course, now we have a cold front coming through so I’m going to have to close it again & I’m sure the mold will come back. Grumble.

I have this problem with a couple of my African violets A LOT and it has spread to another plant before, killing it. Everywhere I read said to remove it with q-tips but that mold really gets down at the base of the stems and is really hard to get at. Once it reaches the root, the plant generally dies. (I have one right now with mold sitting all by it’s lonesome, quarantined, but it’s not doing too badly. One of thos problems is that those plants don’t like anythign wet on their leaves, so sprays aren’t as effective/useful.

I’m definitely willing to try this cinnamon remedy though! I’ll let you know if I see a difference. 🙂

Are they getting good air circulation? Since I opened the window in the room and started spraying them with the cinnamon air freshener when the mold comes back, it’s gotten a lot better. I like using the cinnamon spray because it kills the mold on contact, so I don’t have to scrape it out.

Yup- they do. I don’t put them right near air sources though, only because I don’t want the mold picked up and spread to other plants.

I sprinkled cinnamon on the mold this AM, and I’m really excited to see if it works! If that has any effect and the mold returns, I’ll either try to make my own spray or buy the air freshener.

We were planning on going to the nursery this weekend to start looking at spring things for the garden but it ended up being too cold. I’m hoping the weather will warm up soon so we can get back outside. That’s a really great tip about the cinnamon spray in case we run into similar issues with mold.

I saw you mention on FB that it snowed in Austin! That is crazy. Now I feel bad for complaining about it being in the high 40s/low 50s over the weekend. :/ I am so anxious to plant for spring too, so I hope it warms up for both of us!

I just discovered some mold too — right at the base of the only seedling that has come up. Mike McGrath (of “You Bet Your Garden”) recommends putting 1/2 an inch of peat moss on top of your flats to prevent this:


Unfortunately, I learned of this too late. I’m going to put it on now and hope for the best.

Thanks for the link! Since it’s been chilly this week, I’ve had to close the window and the mold is starting to come back again. I happen to have some peat moss leftover from last summer’s square foot garden, so I’m going to give it a try. I hope it helps with your flats too!

I hate mold…. I mixed soap with water and vinegar in a spray bottle. I tried to spray just the mold. The soap helps keep the spoors down and the vinegar kills the mold (hopefully)
I know that you can use vinegar to bring your Ph down.. and I’v used it in my home to kill mold.. So lets see if it works…

Thanks for the tip! This year, I ended up simply starting my seeds outdoors because I don’t think they can get enough air circulation in our house without keeping the windows open 24/7. :/

I’ve got mushrooms in my seedling flat. I’m pretty impressed by that ridiculousness! What I assumed was white mold was actually fungus spores. The mushrooms are kind of pretty, but I have no idea if they are edible. It would be kinda cool if they were.

Anyway, if I decide to do them in, do you think the cinnamon trick would work on fungi?

Well, I have tried to intentionally grow mushrooms myself and I can tell you that the best way to kill them is to put them under or next to an air vent or someplace else where you get a breeze or draft. They will shrivel up and die really quickly! I’m not sure if the cinnamon works on fungi, but it definitely wouldn’t hurt to give it a try. Good luck!

I’m hoping somebody here can help me. I bought a grow-light and seed starting kit, with a dome and a mat that wicks up water to the seedlings. I, like a lot of you, had a lot of mold growth, and most of my seeds did not germinate. I pulled off the top dome to let them dry out, and a few seeds did germinate, and shoot up, but after 4 weeks, no sign of life in the rest of my trays. Now that I have let everything dry out, I don’t see any more mold. Do I replant in this same “coir” mixture, or do I use potting soil and start fresh? I transplanted my “babies” into peat pots, and they seem to be doing well.

I’ve had this same problem starting seeds indoors; I’ve had such trouble that I’ve stopped doing it altogether! I think I’d try replacing the coir and start over again just in case there’s disease, fungus, etc., still in the trays.

I just planted my seeds two days ago….I used miracle gro potting soil and I have them in various containers…after planting and watering them, I placed them all by a window on shelves and then put a plastic cover over them for a greenhouse effect….this morning I noticed a little bit of mold on a couple…I found this site and discovered the idea of the cinnamon so I have it now sprinkled all over my containers and I also turned on the ceiling fan to get some ventilation going (abit chilly today to open windows, I am in Central Texas)…I guess what I am wondering is do you NOT need to cover the plants with plastic?? I was just under the assumption you did! Now I ma new to all this so there you have that!!! Any other advice would be welcomed also…thank you in advance.

You should keep your containers covered until the seeds sprout; once they sprout, you’ll need to remove the covers or mold will grow. At least that’s what I’ve read. If you have mold before the seeds even sprouted, I’d keep them covered and hope that the cinnamon does the trick!

Instead of using the power, you might want to try Ceylon Cinnamon leaf Oil. It has better staying power than the Cinnamon powder. All you need to do is mix 1% Ceylon Cinnamon Leaf Oil with 99% water in a small spray mister bottle and spray the potting soil to be used for the seedling until damp. Then plant the seedling and water as necessary.

The volatile oil content in cinnamon powder is about 1.1% compared to 100% in steam distilled Ceylon Cinnamon Leaf Oil. Good quality Ceylon Cinnamon leaf Oil also has near 75% Eugenol content, which is the stuff that makes it a powerful anti-fungal.

RE: Mold in soil
I take approx. a 2-cup spray bottle and add 6 or 7 drops of ‘Tea Tree Oil’ to the water. Whenever I see any sign of mold on plant dirt, I spray a gentle mist onto the soil. I let it sit then water with filtered water.
I have found more often than not IF tap water has been used to water indoors and the water is clorinated that is always what seems to start the mold growth.
Tea Tree Oil sprayed on to any type of mold will eliminate it. I use a lower dose when using on plant dirt. *NOTE: It might take 3 to 4 misting applications to remove the mold completely. Then mist one every 4-6 weeks to maintain mold-free soil during winter / spring periods.

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