After I seeded my 32 different tomatoes a week ago I did something I don't normally do and am living to regret it. I covered the pots with a sheet of plastic. I took it off when I saw the first plants emerging. Now I've had some instances of damping off for the first time in my gardening life. I think I'm using the same planting mix that I used last year but I'm noticing on the pots I didn't cover that most of them are staying wet (actually wet wet) for longer than I'd like. The one time I tried a purpose-made seed-starting mix it kept crusting over and the seedlings had a hard time coming out so I went back to planting mix. I should add that the peppers and everything else I started without a plastic cover are doing great. I seeded some more of the varieties that were a total loss and set up a fan to blow for 1/2 hour four times a day just to be safe.

I guess this isn't a request for help but more a word to the wise: If you're using a moisture-retaining mix, don't put plastic on it!

Damping off is so horrible when it happens. On the little seedlings, by the time it appears it's pretty well fatal and nothing to do but start over.

I've never had a problem covering seeds/seedlings on the heat mat. I have an old clamshell that I use for the purpose, and pop it open at least once a day to circulate some air in there. There is never damping off, and the moisture helps them to shuck their seeds. But also using fresh mix for that, so there is no chance of the damping off organisms being present (we hope!).

But I lost a few chard seedlings this winter, in fresh mix but on the cold and damp windowsill. I guess I overwatered for the temperature, stayed wet, got colder and voila. Some lurking pest organism got happy with those conditions, and the susceptible seedlings went down.

What is the ambient temp (assuming inside?) and was it still on heat?

Damping off is something I've seen at times. I will say there is more to it than the plastic. I almost always use a plastic domes to start seeds, and almost never get damping off. Certainly though, the plastic cover did wrong for you in your situation.

For me it usually top watering that initiates damping off, top water and cool conditions. The worse time was when I transplanted small starts of lettuce, spinach, and chard outside in March, into a raised bed and covered with a wood frame and glass lid. It seemed cozy enough for them, but then after a few weeks and a few weather changes, they started damping off like dominoes from one starting point.

My latest bout of DO was early this year. I started onion seed but wasn't really clear headed about it. I didn't want to start the lights yet, so I used an upstairs window area. I did them in 48 oz plastic dairy dishes (deep, for onions) and covered with saran wrap and on a heat mat. But the heat mat was near a window, for light. Well, the heat pretty much never shut off because the tubs lost so much heat. And when it was very cold outside, the temp dropped more. When one tub of seed started sprouting, I took the plastic off of it, but left the tub on the heat mat- MISTAKE. The tops immediately dried out, and no more seed sprouted. After a while with no more germination, I top watered to try to keep the seed wet for germination -MISTAKE. Within a few days, whoosh, they started damping off. I planted in excess of 250 seeds and have about 15-20 from a single container that still looked good by early March. About half of that container had damped off. Everything else that had sprouted in all the other containers damped off.

I use compost in my mix, so it is not "soiless". But DO is rare for me, thankfully. I have not had an issue with damping off at any other point this spring and that at 12 or so 1020 trays and counting. But very late winter and early spring with cool temps is when I have experienced problems.

I bought some diatomaceous earth this year, in the form of autozone oil spill absorbent. I have been playing with it some. Right now I have dense planted seeds in it, just 100% DE, and they popped right up and look okay, if a little leggy. I didn't have room under my lights to start any more trays, so I'm doing it this way in one just one tray and will transplant when I have room for more trays.

The DE is pretty neat though and I plan to implement the DE in my seed starts, most likely as a top cover when it is colder. The seeds sprout quickly, the way it holds water. I'm thinking I'll keep the base mix the same, plant seeds on top or just into it, then cover with a 1/2" of DE. edit to add: AND NEVER TOP WATER AGAIN

Twice I attempted to grow seedlings using domes and both times I had damping off issues. Since then I have never even considered using one. I know that many people have great success covering their seedlings but not me. Domes off, some mycos added and I have never looked back.

Bower wrote: ↑Sat Apr 08, 2023 1:56 pm I've never had a problem covering seeds/seedlings on the heat mat. I have an old clamshell that I use for the purpose, and pop it open at least once a day to circulate some air in there

I put the plastic right on top of the pots. I'd lift it now and then to check on things but that was a pretty close air space. I wonder if using a larger cover would have made a difference.

JRinPA wrote: ↑Sat Apr 08, 2023 2:40 pm What is the ambient temp (assuming inside?) and was it still on heat?

I checked and the room is 66ish. At our old place the basement was cooler. These pots were on heat 24 hours a day, same as the peppers.

JRinPA wrote: ↑Sat Apr 08, 2023 2:40 pm I bought some diatomaceous earth this year, in the form of autozone oil spill absorbent. I have been playing with it some. Right now I have dense planted seeds in it, just 100% DE, and they popped right up and look okay, if a little leggy. I didn't have room under my lights to start any more trays, so I'm doing it this way in one just one tray and will transplant when I have room for more trays.

Interesting. I never would have thought of using DE. What size are the pieces? I always thought it just came as a powder. Do you have to worry about inhaling dust?

I should add that I made an attempt to sift the potting mix using a colander I picked up at Goodwill. The holes were too small and I ended up with essentially straight, fluffy peat. I did some plants in it, though and they came out fine. Not tomatoes. I went back to using the mix straight from the bag just picking out the sticks and chunks as I go.

10 to 1 ratio of water to hydrogen peroxide does the trick for me.
Use it from the very start before seeds sprout in a spray bottle.

About sifting, I use two sifters, a 1/2" hardware cloth grid for peat moss. And a 1/4" grid for vermicompost. If I tried to sort the bagged peat moss with a 1/4" grid, I think I'd throw half of it away. This last bag we bought is lousy with chunks. The only time I sift peat moss really fine is for 3/4" soil blocks.

I haven't had great luck over the years using saran wrap as the plastic for seed starting. Didn't work great this year, either. I know some people use it successfully. But I like 2" high clear lids. They look just like a 1020 tray, but thin and clear.

Definitely the dust is an issue with DE. What I do is hold my breath, pour, and run out the door to let it clear. Ah, if only I were kidding. I'm used to doing the same with perlite, but there is more (and probably worse for you) dust in the DE.

For particle size I took a pic. The oil spill stuff is fairly fine; not flour size, but it is much smaller than the luna rock perlite (right) I typically use for 25% of my soil block mix. The bag was 9.99 at autozone a month back, and it was just inside the door about 10 ft at that particular store.
I read about using DE oil absorbent for seed starting a while back. There was a long standing thread on tville. But this past month is the first time I bought some and I have been playing around with it. The amount of capillary action is amazing.

JRinPA wrote: ↑Mon Apr 10, 2023 12:28 am I read about using DE oil absorbent for seed starting a while back. There was a long standing thread on tville. But this past month is the first time I bought some and I have been playing around with it. The amount of capillary action is amazing.

Cool! Thanks for taking pictures and everything. I vaguely recall using perlite to cover the seeds on top of some other mix at one time. I also remember once trying to pre-wet the perlite to keep the dust down and ending up with my hands looking like I was wearing lumpy white gloves. That stuff sticks to everything when it's wet. Maybe I'll try the DE on top of a sterile mix as well as straight. I will have to watch nutrients then too.

@worth1 So you're essentially just watering the pots with the peroxide mixture? Not just a one time application?

DriftlessRoots wrote: ↑Mon Apr 10, 2023 6:09 am

JRinPA wrote: ↑Mon Apr 10, 2023 12:28 am I read about using DE oil absorbent for seed starting a while back. There was a long standing thread on tville. But this past month is the first time I bought some and I have been playing around with it. The amount of capillary action is amazing.

Cool! Thanks for taking pictures and everything. I vaguely recall using perlite to cover the seeds on top of some other mix at one time. I also remember once trying to pre-wet the perlite to keep the dust down and ending up with my hands looking like I was wearing lumpy white gloves. That stuff sticks to everything when it's wet. Maybe I'll try the DE on top of a sterile mix as well as straight. I will have to watch nutrients then too.

@worth1 So you're essentially just watering the pots with the peroxide mixture? Not just a one time application?

No just spraying the surface of the soil occasionally.

I prefer DE over perlite in my mixes for drainage because it holds more water than perlite. However I now use more perlite because it is cheaper and does hold a little water. I purchased a 2 CF bag from Home Depot for 18 bucks (free shipping). I use one of my soil sieves to sift out the larger stuff which I use in the larger containers. I always work with DE and perlite outdoors with a little breeze to avoid the dust. I water from the top once or twice per day using a squeeze bottle with a drilled rubber stopper and piece of tubing. Water gets on the leaves and stems but the plants do well.

I don't use any sterile mixes and don't clean my reused pots. I don't apply any medium to the surface because I like to see the surface and judge the need for water. I use growing conditions to avoid damping off. I try to avoid cool and damp conditions and use UV from the sun to sterilize. I carry the plants out every day weather permitting. I don't know how much UV I get from my grow lights. I had a lot of damping off when I used the *tough love* approach to my starts. I would take them outside no matter the weather and let them deal with what ever conditions.

Good drainage in the mix and avoiding cool and damp and sunshine helps a lot with avoiding damping off.

Did you have the plastic on when the plants already sprouted? I do domes but remove them once they sprout

Moth1992 wrote: ↑Mon Apr 10, 2023 4:07 pm Did you have the plastic on when the plants already sprouted? I do domes but remove them once they sprout

Some had just broken the surface when I noticed and removed the plastic from all.

I always use Ultrasorb from AutoZone. They used to have finer grains years ago when I bought my first bag. It lasted a while cuz I do mass sowing so I don't need much for 10 to 20 4-inch pots, about 15 seeds each. Now the Ultrasorb has bigger sized grains so I was hesitant but they worked just fine.
And yes, I always use the dome that came with the heating pad & remove the pots as soon as I see multiple sprouts. No problem.
I use seed sprouting mix or potting mix for smaller seeds like basil, & cover with plastic wrap with holes punched in. But I remove the top as soon as I see even a speck of green cuz if I leave it too long I've seen white furry mold appear. And you don't want to risk that.

Well I still manage to screw it up once in a while.

This cup is half my eggplant starts, that should have been started in February with the hot peppers. So these are Santana, treated with thiram I think. The other cup, not shown, is Dancer, untreated, and still not showing any up... Both are older seed, but the Dancer is pricey stuff from Johnnys, Santana is cheap from the produce supply.

The cups were on heat mat, under dome, and the Santana sprouted in expected time. Last night, after 3 days of them up, I checked it and it felt very dry. The composition is compost on the bottom, and floor dry DE on top. 1/4" layer DE, wetted, seeded, 1/4" layer DE wetted, set under dome on 79F mat. Sprouted good but cup was very dry and hard.

So last night I set it in water, but it wasn't soaking much up after a couple minutes. Should have stopped there. Against my better judgement, I added water to the top until it felt like it took some water on. I forgot to dust it with more DE afterward...that is something I've been doing. When in doubt, backfill it will more dry DE on top.

After watering I put this eggplant cup with my pepper tray, under the lights. Fan on with the lights during the day. The ambient basement temp is 57F right now.

I just went and checked it and since watering 18 hours ago, even with the DE on top, one of the eggplant has damped off and keeled over. Not sure how many more will follow. I saw at least one more with brown growth at the base.
Seems like every time I top water I am rolling the dice, but I still end up doing it. Probably a lot of times I'm tired and not thinking straight.

That's so sad but it's also how we learn. I started using mycorrhizae in my seed mix along with the DE and it sure seems to help keep the other fungal things at bay.

How did the humidity domes and plastic wraps get established as the fashionable or right thing to do initially? Has it always been this way? Is there a plastic wrap guru, a Charles Dowding of domes? Are plastic wraps and or plastic domes completely and absolutely necessary or the best practice to get good germination in a relatively dry northern climate, like the seeds won’t germinate otherwise?

Genuinely curious as someone that has never started seeds under a plastic wrap or a plastic dome or experienced dampening off.

karstopography wrote: ↑Tue Apr 02, 2024 8:47 pm How did the humidity domes and plastic wraps get established as the fashionable or right thing to do initially? Has it always been this way? Is there a plastic wrap guru, a Charles Dowding of domes? Are plastic wraps and or plastic domes completely and absolutely necessary or the best practice to get good germination in a relatively dry northern climate, like the seeds won’t germinate otherwise?

Genuinely curious as someone that has never started seeds under a plastic wrap or a plastic dome or experienced dampening off.

I myself never use them. I used them once and it was a disaster.

I cover my seedlings with communion cups. They can be removed individually, and it has gaps at the bottom for air circulation. It works well.

Yeah it is too cold otherwise. 55F, not much will sprout. Actually 53F in February. Put heat under it, you can get it to 75, maybe, but the top constant dries out. With a fan blowing, oh boy it really dries out quick.

MissS wrote: ↑Tue Apr 02, 2024 8:27 pm That's so sad but it's also how we learn. I started using mycorrhizae in my seed mix along with the DE and it sure seems to help keep the other fungal things at bay.

That's something I've been doing for quite a few years now - adding a little mycorrhizae to the seedling mix I make. First, I "bake" it, in my grill, in some foil pans, to about 200°, then let it cool overnight. Then I dump it in a bucket, and mix some myco into it, along with some Bt israelensis in some water, to prevent fungus gnats. That mix I make I put some DE granules in, but much more perlite (at least 20% volume), and test it for drainage, before doing the baking. I always cover trays with the lids, but as soon as I see a hint of sprouting, they come off, and never have a problem, KOW. Often, before the seeds sprout, I'll start seeing the cottony like growth on the surface of the soil, from the mycorrizae.