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White mold keeps forming while germinating?

Kilgore, TX(Zone 8a)

White mold is forming on top of soil of seedlings. Does this mean seeds are getting too much water? The one tray is a self-watering tray, so I can't control how much water each one gets. I've been brushing it off w/my fingernail. But will this have some effect on the seedlings? Should I transplant when that happens? Some of them are only 1/4 inch tall, if that!

Frederick, MD(Zone 6b)

Sounds like too much water, yes. With bottom watering, the surface of the soil stays relatively dry (may become a little moist the day you water), and that really helps with a lot of stuff like that. That mold might be harmless, unless it smothers seedlings. However, seeing that mold may also mean you've got good conditions for damping-off... and some of the same preventative steps & remedies (fan, hydrogen peroxide) for damping off may help with this mold, too. See the article I wrote on preventing damping-off: http://davesgarden.com/guides/articles/view/277/

Greenville, IN(Zone 6a)

I've got it too, I've never had this white mold before, my basement is damper than usual so I chalk it up to that, peroxide doesn't help, I've tried :) If you let your dirt dry out a little it doesn't help much either! I have left my seedlings in there until I could transplant them and doesn't seem to bother them and I've had seeds germinate in it that have been so small I couldn't put in another seed tray but it makes me very nervous!

Nilwood, IL(Zone 5b)

I put sand on top of mine and it seems to be working. BEV

Greenville, IN(Zone 6a)

What kind of sand do you use and where do you get it?

Nilwood, IL(Zone 5b)

I just use regular sand from Rural King store in a bag. I use the rest for ammending garden soil. BEV

Greenville, IN(Zone 6a)

Thanks Bev !

Nilwood, IL(Zone 5b)


Kilgore, TX(Zone 8a)

I took it off it's watering tray & I'll see if that helps. Hopefully in the next day or so I can transplant! Meanwhile, I'm just scratching it off the surface of soil w/my fingernail. I'm afraid to try cinnamon, but that I probably would try, if I heard other people that had luck with it too! I'm very nervous because I have about 200 seedlings in this tray!

Nilwood, IL(Zone 5b)

I did forget and am sorry. When I first had seedlings I did put cinnamon and it does work. Thanks for the reminder. BEV

Montreal, QC(Zone 5a)


I noticed your quandary and just wanted to add my experience.

I have heard many gardeners singing the praises of bottom watering, but have never had much success with it myself. We have always top watered our seedlings and potted plants, with great results. We use a bottle top rose for precision; anything else tends to over water. Damping off is usually not a problem, although some genera are more susceptible than others. The key is not to over saturate the soil, and also to water less frequently. We follow the school of thought that seedlings and plants should be watered deeply when they begin to dry out, and then left until they begin to dry out again. We find that in our plants, this encourages deep roots and does not lead to damping off. We have had the same troubles with peat pellets, as they also sit in a watering tray and absorb water from the bottom up; they grew white mold in the netting of the pellets, and I have had to adjust the amount of water that I put in the tray and how often I do so. They are a bit trickier than regular pots of soil.

If you are seeing mold, it is a sure sign of too much moisture for too long; mold will grow when there is a constant source of moisture. Have you removed the cover or lid to your tray? That needs to be done as soon as you see signs of germination. That will allow for good ventilation and prevent a build up of humidity in which mold spores thrive. You might try an anti fungal product such as no damp, there are many others as well.

That is just my experience, thought I'd add it to the list! Good luck with your seedlings,


Kilgore, TX(Zone 8a)

Thank you plantenthusiast. I did remove cover right away after seeing some seeds germinate. That I got in the directions. But they don't give you directions, if you start seeing white mold!! They really should! But that's okay, since I have all of you knowledgable gardeners and enthusiasts! Thank you everyone, for taking the time to post all helpful suggestions. I appreciate it as a very new gardener. And maybe one day, I'll have an answer to one of your questions! (hugs)

Greenville, IN(Zone 6a)

I water my seedlings from the bottom but I take them out of the water before the whole top of the soil is wet, I just watch for the water around the plants stem then take them out to drain for a while then put them on a cloth to take the extra moisture out of the pot, I just want my seedlings damp not saturated, the white mold is in my seedling trays mostly, I just try and pick it off until it gets too bad then on the ones I can I take the seedlings out and replant them, what a pain lol

This is just the year for white mold apparently, too many people are getting it must be the dampness in the air too. My basement is so damp from all of this rain and the house is too, it's been too warm to have the heat on I just turn it on once in a while to try and get the dampness out, now the furnace is on cause it got cold again lol I just keep running the heater the fan in with the plants they are shut off from the rest of the basement and I'm hoping this helps!

Indianapolis, IN(Zone 5b)

Hey! I have a flat of Phlox I am trying to germinate and I put one of those hard plastic tray covers over it to keep it moist enough so I don;t have to water and dislodge the seeds, and I have a very wispy white mold in a lot of places. Is that what you guys are talking about? I have never seed it before. It is very light and airy and wispy looking -- like dandelion fluff or fluffier.

My idea is to spray the flay 1/2 with bleach water and 1/2 with H2O2 to see which is better. I am looking for a piece of cardboard the right size so I can do my little test.


Kilgore, TX(Zone 8a)

Yes, exactly llloquin. Good description. Mine went away since I took self watering tray away. I'd use the cinnamon idea, seems more natural. Michelle

Greenville, IN(Zone 6a)

The bleech has got to work bettr but I'm afraid to try it something about bleech and plants that I don't trust :) Let us know your results Suzy :)

Southeastern, NH(Zone 5b)

I have some of the same mold as Suzy described. I think it is from the seeds, because it only is on certain ones not all of them and they all were watered the same way. I notice some seeds mold up when doing the baggy method as well, while others don't. I read somewhere that if seeds are not dry enough this will happen. So maybe some of the seeds in the batch were not dry enough. It hasn't bothered the seedlings that did germinate for me either. The only thing I did different was use wood sticks for labeling and those were the first thing to get the mold. So initially I thought it was the cause. The seeds I've noticed have it are all malva - alcea & moschata. They are all from different sources. So it isn't just a bad batch.

Greenville, IN(Zone 6a)

Meredith I've used those popcicle sticks and they always got mold on them I don't use them anymore.

Cochrane, ON(Zone 2b)

Just a thought, but have you ever tried to cover your seeds lightly with vermiculite? I do this on some of mine & have never had the mold problem.

Kilgore, TX(Zone 8a)

I've thought of Vermiculite, but what exadtly is that? Do you buy it pre-mixed? Michelle

Cochrane, ON(Zone 2b)


Fifth item from the top. I use it for starting seeds & propagating cuttings. Just don't breath in any dust that might be in the bag. There are various brands around.

edited to add that you have to select 'Soil Conditioners' & then it is 5th item down.

This message was edited May 4, 2008 1:32 PM

Brooksville, FL(Zone 9a)

well thanks to this list and this thread, I now for certain that this is my problem.... too bad as I had such a great start to my horse hair grass to now loose all 50 plants.

My mistake was watering too much and having too much moisture in my little greenhouse.

thanks folks

North of Atlanta, GA(Zone 8a)

Great thread. This is my first year starting from seeds and I've had a few problems with the white, wispy looking mold. Never thought about posting a question on the threads. Thanks for all the helpful info. Love this website.

Frederick, MD(Zone 6b)

Welcome, Lili! I'm glad you found DG and decided to subscribe... it's about the best $20 I spend on my garden (or myself) all year, I think. :-)

Meadow, I'm sorry you lost all those seedlings... sure hope the problem is now solved for you!

Brooksville, FL(Zone 9a)

Well funny thing, I went back and uncovered the green house and sprayed all of them with Hydroproc.... (sp) and now after having a growing light on them most of them have grown a 3rd new grass blade. The mold is still on top but I'm hoping I can get them outside before the end of May, only time will tell if they make it...

Frederick, MD(Zone 6b)

Hooray -- what tough little guys! Can you pick the mold off the top of the pots? I've done that with similar stuff, doesn't always stop it but it can slow it down until I can get the pots outside, which usually solves the problem.

Brooksville, FL(Zone 9a)


The mold is not so bad and if we continue to have more wonderful days like the last two days, then won't be long till I can get them outside... and possibly save them. I just picked up some cold frames and I'm thinking of putting them out in them, with a small crack so that the humidity doesn't build up too much.

Frederick, MD(Zone 6b)

Sounds like a plan... good luck!

Brooksville, FL(Zone 9a)

well, they all started coming back, even though the white mold was growing as well, so I put them outside inside a new cold frame that I just picked up from a guy in my garden club and totally forgot all about them. So as you have already guessed, I killed all of them.

Now I'm starting over.

Ames, IA

Oh that is so sad!
I wanted to also say that I have started to cover some of my seedlings with vermiculite and have yet to have a problem with mold or damping off.
Also, once the seeds germinate, to prevent damping off and mold problems in general, I have found it very useful to use a small oscillating fan several feet from the seedlings. The air circulation not only prevents mold and deters other nuisances, but it also strengthens the stem of the plant so that it isn't floppy when it gets put outside.
Good luck everyone!

Brooksville, FL(Zone 9a)

Yes I know that my problem was I let it get to humid inside the little greenhouse and that is what started everything. I hated that I lost them especially since they looked like they were overcoming the mold. But this was a learn for me. Now when I use it next year I have a grow light and a small fan that I believe will help me be successful and being a member here at DG as I've learned a lot from everyone here that posts their questions and those who take the time to help answer those posts.

Thanks everyone.

Now I have the cold frames set up and I'm going to be planted some more grasses. My plan will be frame closed at night, as we are still having temps in the 40's at night and open during the day, as this is on the south side of the house and it gets plenty of sun.

Can't wait to see what I can do with cold frames. I've always wanted to have some cold frames so I could get a jump start on spring growth.

I've been reading a lot of the threads in the overwintering forum. Great stuff.

Northern living is such a change to my own past experience with growing.

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