I just moved my plants into the little greenhouse last Friday -- 5 days ago. The herbs had been hanging in the sun and were doing great. Today I stayed a little longer in the house and noticed some white mold/mildew looking stuff on top of the dirt on two herbs ! I scraped it out, put them back in the house and turned on a second fan--and then inspected all the plants. It has been humid, but sunny until yesterday and today is rainy. I'm not sure if the plants were just too wet when I put them in there ?? This stuff grew fast. Is there something else I should do or put on them? I hate to use chemicals - especially on herbs.

I had added two new herbs over the weekend, but they don't have the white mold. As I was standing there though I did notice the dill had a green worm on it -- eew ! Where did that come from -- I evicted it.

Any ideas on the white mold/mildew would be greatly appreciated -- I'm a novice and need all the help I can get !

Thanks much.

Uh, oh, Carol the green worm on the dill may have been a little butterfly caterpillar. Here, the black swallowtail butterflies love to lay their eggs on my dill, and when they hatch (until the blue jays discover them) the little green caterpillars devour the dill. Most likely there was an egg on the dill somewhere when you brought it into the greenhouse. Yes, it will eat your dill, but the plant will grow back and the caterpillar will cocoon and make a butterfly . . . your choice. You may see more.

Same with the white moldy stuff. It was almost certainly in or on the soil when you brought it in. Spraying with a very mild solution of baking soda - 1/2tsp. per quart of water - may help to keep it from progressing, but to hope there will be no fungi in your greenhouse is pretty much futile. It's an ideal situation, moist and warm, for the growth of fungus, and until you get it under control in the greenhouse, it will spread around a bit via air movement.

Good 'housekeeping' is the answer. Scrape or scoop it off wherever you see it on soil or pots. Remove every leaf that has any on there and bag them in plastic so the spores can't escape. Keep this up for the next few weeks and it will get to a manageable level. But keep an eagle eye out. Spray unaffected foliage and soil surfaces with the baking soda solution. It changes the pH on the surface of the leaves and soil to make it unhospitable to the spores.

ELAINE thank you for you response and advice -- I'll try try the soda.
I didn't even think that the worm might be a butterfly caterpillar. Darn ... I love them so.
Thanks again :)

You might try brewing some chamomile tea and, after it cools, spraying it on the plants and the soil. It has anti-fungal properties. I'm not sure what it will do to an existing fungal problem, but it's been effective as a preventative on the seedlings I start indoors every winter.

KENT. Thank you. Interesting idea. I had no idea. I will try it.

Another anti-fungus spray is diluted hydrogen peroxide. You can water with it or just mist the surface, and/or spray leaves with it.

I don't know about spraying with peroxide and baking soda very close together. It might be OK, might not be, or might nullify the effect of either or both.

I think that there would be no downside to alternating chamomile tea and peroxide. Or just pick one and use it until it seems less effective, then try the other for a while.

0.2% hydrogen peroxide:
dilute "drugstore" hydrogen peroxide by 1:16 -
1 tablespoon per cup of water
2 ounces per quart
1 cup per gallon

Preventing fungus, no matter how hard, is probably easier than curing it once established.

P.S.
You should get some improvement just by keeping the soil surface drier. Less frequent, heavier watering helps with that. Air movement (a fan) or lower humidity would help dry the soil surface somewhat. Bottom-watering (if convenient) should help.

I think the best way to get a dry soil surface is to top-dress each pot with relatively coarse bark nuggets. Gravel or pebbles ought to work too. Very coarse Perlite should stay a little drier than straight potting mix.

Besides being drier and therefore less fungus-friendly, top-dressing can make the exposed surface less "organic" in the sense of less digestible fungus-food exposed to spores in the air. If you have compost in your potting mix, that feeds fungus like candy. If you use organic fertilizer like fish emulsion, that also provides fungus with easily digestible food.

If you ever re-pot the herbs, using a faster-draining and less-water-retaining soilless mix helps.

Probably any soilless potting mix is less fungus-friendly than any kind of potting soil, or any mix with any garden soil in it.

RICK. Thank you for all the info. I will try several of these methods. I did add some compost I had been making in a bin and it wasn't quite composted. So that probably is the culprit. Sounds like I may need to remove some soil and replace. And will try some bark on top as you suggested. Today I misted with chamomile tea. If that doesn't slow it down I will try your peroxide solution next.

Thanks very much. Carol.

Ecscuba said:...
I did add some compost I had been making in a bin and it wasn't quite composted. So that probably is the culprit.

A hah! It's a good outcome when an answer is found.

It'll be even better if some combination of factors cures it for you!

Hopefully it will be cured before they spread too many spores around your greenhouse.

Thank you for your kind words.

Cleaning the greenhouse like a compulsive maniac, and creating low humidity for a week might (I think) reduce the number of fungus spores down to what you would have anyway just from having airflow and dust. But I think at most that reduces "trillions" of spores down to "millions" of spores. No one can ever get rid of all spores.

"Everything is everywhere: but the environment selects".

I don't know whether cleaning with chlorine bleach or stronger hydrogen peroxide is better for discouraging mold and fungus. Modern "oxygen" bleaches might be easier on fabric colors, but they don't sterilize or disinfect worth a darn.


I'm trying to think how to add organic matter to a potted plant without encouraging fungus, mold or other nastiness.

Incorporating well-aged compost or other sources of organic matter into the deeper soil during potting but not into the surface layer might help.

Leaching soluble stuff out of the top layers with heavy top-watering might help a little, if that doesn't make your pot more water-logged!

Bottom-watering with something like fish emulsion might keep it OUT of the top layer of soil, OR it might leach everything soluble upwards until it winds up in a crust on the surface!

What do y'all think, would making compost tea from well-aged compost increase or decrease fungus in pots in a greenhouse? Would it add microbes likely to discourage fungus, or would it just feed the fungus?

Rick's "Cleaning the greenhouse like a compulsive maniac," is probably the most important thing for right now, I think.

You're working to control new spores taking hold with the tea spray or peroxide (I'm going to try that to zap black rot on my orchids next summer!).

But you need to remove as much of the visible mold as possible. Any still growing colonies will be releasing spores, as Rick says "by the trillions" if you leave it. Not only the leaves with visible mold, and the soil surfaces that have it, but also if you have wood shelves or any other surface that could possibly be receptive. Even if there is condensation on the glass and metal surfaces of the greenhouse itself, you should wipe those, too. I'd definitely use the peroxide solution for that.

This is the first thing I saw when I came to the forum today for the first time.
I was going to ask which fragrant herbs (hoping lavender for sure) I can grow (not necessarily to eat) in the ground in the 10x10 space at the front fence that I know has powdery mildew. Any suggestions for this situation? I'm hoping to give the pedestrians lovely smells. I can grow my edibles elsewhere.

I am not sure about the mildew issue, but here are some ideas for nice looking fragrant herbs. And of course lavendar and sage are obvious choices as well, so many varieties. Mints if you can contain them. And perhaps underplant with chamomile to counter your mildew problem.

Thanks.

See, I didn't know chamomile was any use at all for powdery mildew!
Thanks extra for that!

Another one I like (and also treat as an annual) is cedronella, which smells much like citronella with a pretty blossom. And many hyssops have good fragrance, anise in particular.

Thanks.