Peat is molding?

milocrabDecember 2, 2011

I made a soiless mix using grit (2), akadama (1), perlite (1), and peat (1); and planted some tatsoi seedlings in an 8 cm cup that has plently of holes at the bottom. They are under 2x39W T5HO tubes with a fan blowing at all times. The temperature is 76-78F, relative humidity is 40%. I water every 2nd day; usually the top layer of the soiless mix appeared dried before I add water. Yesterday I noticed some white mold developing, mainly on the peat, but I also see those hairly, web like mold on the akadama and grit as well if I look closely.

I searched this forum for the keywood "mold" and realized most type of mold won't do harm to the plant, and I had probably watered too much which leads to molding. However I had a fan running at all times, air circulation is extremely well, and I only watered every 2 days with just enough water to come out at the bottom. I wondered if there are any other factors that could lead to molding. Our tap water is PH 8.4, so I added a bit of white vinegar to lower the PH to 6.2. Can vinegar contribute to mold? Eventhough a bit of mold is probably fine, but I'd still like to get rid of, or prevent it if possible. Would microwaving the peat before use be any good? How about replacing the peat with coir? I heard coir suppresses mold.

Here is my Tatsoi seedling, note the white powder like mold on the peat:

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I can't really answer why your medium developed mold, but I can tell you from experience that cocopeat will develop mold, too... in the strangest colors I've ever seen!

Quite some time ago, I was told that cocopeat was a great product for container growing, so I tried it. I found that it held way too much moisture for long periods of time, and it did mold in strange orange, red, yellow, blue, and green molds that I had never seen before! I abandoned its use.

Today, I use a mixture of fir bark, perlite, granite chips, and turface. I also have some Leca or Akadama for other growing purposes.

My guesses would be an environment kept too wet... or items that weren't as clean and sterile as you may have thought? I'm not really sure.

    Bookmark   December 3, 2011 at 9:33AM
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tapla (mid-MI z5b-6a)

The medium looks great!

Are you sure it's not just from water wicking to the top & evaporating, leaving dissolved solids behind (the 'mold')?


    Bookmark   December 3, 2011 at 10:39AM
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I'm very sure its mold, because it is looking even more moldy today! I tried to remove the moldy pieces and the whole top layer of the mix is like a pancake. Held up the cup and looked at the bottom holes, I see mold there too! (There is also a root sticking out, is it time to transplant to a larger pot?)

Perhaps my medium might not be clean and sterile to start with, as I used them straight from the I suppose to rinse them with boil water or microwave them before use? I have a few "test pots" that I started a week earlier, they aren't doing well either because I put in too little mix; however they aren't molding - the only difference is that I microwaved the peat for those pots. Perhaps microwaving the peat first would help?

    Bookmark   December 3, 2011 at 8:04PM
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I have another question regarding when to transplant. The cups that I'm using now is 3" diameter x 4" tall, most of the seedlings have one pair of true leaves. I'm growing mainly greens and brassicas, shall I move them up to a larger pot step by step (several transplants), or shall I move them to their final pot now? For example, I have some cabbage seedlings, they'll eventually go into 10" pots. Shall I move them now? Or keep them in the same cup until there are 3-4 pairs of true leaves? Then move them to an intermediate 6" pot or the final 10" pot? I'm confused.

    Bookmark   December 3, 2011 at 8:20PM
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tapla (mid-MI z5b-6a)

Since I don't know what you're dealing with (the mold), I can't help much. Steam sterilizing or microwaving until the moisture in the mix is turning to steam should kill mold spores, though.

How large you can appropriately step up to in pot size is closely tied to your choice of soil. You need to be very careful about how large the pot you bump up to is when using heavy, water retentive soils, but as the soil porosity increases and the ht of the PWT decreases, it becomes commensurately less important; until finally, when the PWT is very low or nonexistent there is no limit to pot size on the 'up' side.

You're safe if you pot up at any point before the root and soil mass can be lifted from the pot intact. Root masses left to become congested beyond that pivotal point should be expected to have a permanent negative effect on growth and vitality unless corrections are made by root pruning efforts.


    Bookmark   December 4, 2011 at 4:52PM
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Thank you Al :-)

I transplanted several of the non-moldy ones (which happen to be the first test batch that were planted in paper cups with too little mix) into 8" pots yesterday. Some of the roots were grown into the paper cup, I did my best to be as gentle as possible, but still broke a few of them when trying to get them out. Let's hope they will survive the transplant.

I decided I will just leave the moldy ones in their 3" pot, and harvest the young leaves when they outgrow that pot. Greens grown in moldy mix is not harmful, is it...? Besides the presence of some white mold, the seedlings appear very healthy to me.

    Bookmark   December 4, 2011 at 7:29PM
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tapla (mid-MI z5b-6a)

Plants grow in harmony with thousands of species of fungi/mold - some beneficial. I wouldn't get all afluster over it unless I saw some convincing evidence the apple cart was about to get upset. ;-)


    Bookmark   December 4, 2011 at 8:18PM
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