Misting does very little to improve low humidity.

Without seeing a picture of your rosemary, it is difficult for anyone to accurately diagnose the white powdery film. I suggest that you investigate Powdery Mildew, however. That's a disease that is quite common on rosemary plants brought inside for the winter.

Here is a link that might be useful: click here for information

Yuck...that sounds like what it is. I didn't realize misting would be so bad for rosemary, but apparently it is.

I didn't see any info in the link on whether there's a way to 'treat' the leaves...like rubbing them with alcohol or anything? Obviously I will stop misting the leaves but it sounds like I need to do something to get the current mildew OFF..but I'm not sure what.

Also, I didn't realize that ...it says rosemary doesn't like indoor temps below 70. But then, surely in its natural habitat it experiences temps below 70...so why can't it take temps below 70 indoors??

I can try running a fan for an hour or so each day by the plant, but obviously I'm not going to run a fan 24/7 during the winter months, just to keep one plant alive...much as I'd like to have my rosemary stay alive indoors...

You're quite right. Rosemary is perfectly capable of taking winter temps below 70. It grows outdoors year round here and survives happily down to the mid 20s for brief periods ie a few days. It will not freeze totally like a tropical plant. In fact 70 would be a hot summer day here. Such a high temp indoors would just encourage etiolated growth. I'd overwinter it in the coolest, lightest, airiest indoor space you have. If it's in a pot I'd even put it outdoors for some fresh air if you get some mild spells. What is the temp there now? Does it even need to be inside yet?

NYC just had quite the heavy snow storm a week ago. I'm at the other end of NY State and saw only a few flakes last week but saw 70 degrees F yesterday. Our weather is highly variable this time of year so it is a guessing game at best if leaving tender plants outdoors a bit longer. But outdoors during the day -- if you can remember to bring them indoors at night -- is a great suggestion to give the plant what it needs for a little longer.

FataMorgana

I am able to over winter rosemary in Massachusetts by bringing the pots outside on the deck when the weather is above freezing. Bright UV sun, wind, and rainfall to wash and hydrate the leaves are essential for survival. Inside my house I use a bright LED light, a sunny window, frequent watering, and a humidifier, and the rosemary barely survive until I can move them outdoors. My main problem is that my house is hot from being super insulated and heated with a woodstove operated by my children who love to chop and burn logs.

You need to re-read that link. It says that 70 degrees is a temperature that favors powdery mildew....nothing about what is ideal for the rosemary. I attached the fact sheet to inform you about the disease, not the cultural conditions best suited for rosemary.

Your plant would be far better off if allowed to live outside in all but the coldest of temperatures. However, the powdery mildew can cause real problems if not corrected. It's a disorder that can be prevented, but once the cells become infected, it is all but impossible to cure, especially on edibles. If allowed to grow unchecked, PM can kill a plant.

Rosemary is grown outside here, all year. It does make a difference that it is planted in the ground, but we see winter temperatures in the teens and twenties.

Thanks all. OK so it sounds like I should continue to leave the rosemary outdoors and just bring it inside anytime the temps below say freezing?....or just below say 20 degrees?

And is snow in and of itself bad for rosemary? If it snows, but the temps are say 30, should I still leave it out, or should rosemary never get snow on it?

Also, does anyone know if there's anything I should be trying to do ...like wiping the leaves off with anything...since it currently appears to have PM on it? Or would that not make a difference and I should just concentrate on putting it back outside and making sure to never wet the leaves again?

btw, I'm very good with taking care of my plants as if they were 'my babies', so I would definitely never forget to bring them back indoors once the temps dip to a certain level... ;-)

Thanks!

My rosemary has had snow on it many times in its 20 year life. It's long and persistent heavy freezing it can't take, not snow per se. Google images of 'rosemary in snow' if you are doubtful.

I don't think that misting in itself would be enough to cause powdery mildew as indoor air during the cold months is generally pretty dry and the mist generally dries quickly. Probably the mildew started forming when the plant was outside.

There are fungicides that you can spray that should eliminate the powdery mildew.

Ok, well I decided for the time being to put the plant back outside...

But something else I noticed... As mentioned, I'd kept the plant sitting on a tray of water. The pot was elevated on pot feet, so it was sitting just OVER the water.

Today as I removed the pot to put outside....I saw three very skinny worms in the water...they were about 2.0-2.5 inches long...and very skinny.

What the heck might have caused that...and do you think they came down from the soil through the drainage holes, or might they have formed in the standing water? Btw, I probably last added water to the dish about two days ago...

Tx!

Again...guessing without an image, but your description of the worm makes me think of Gordian worms. The adults are found in standing water or very damp soil. They are a parasite of crickets and grasshoppers.

I don't understand why you had it sitting over a pan of water. I thought rosemary liked it on the dry side.

I think the operative word is 'over' not 'in'. Presumably it was intended to keep up humidity around the plant, not in the potting medium.

Yes...I had the pot sitting elevated over a dish of water, thinking it would help with humidity. I'm not in a position to run a humidifier or a fan 24/7, so figured sitting it over a dish of water might be the next best thing. That, and misting the leaves (which I've since learned is NOT good)...

Late to this thread, but I just wanted to say that I've kept a rosemary plant over 2 winters (this will be my third) in a large north facing window, room temp will always be in the mid to lower 60's, and I water it about once a week. It has done just fine. I do wait until nighttime temps are consistently below freezing before I bring it in -- so it just came in last Friday. Up to now, I've been covering it for the nights we had temps 32 & below.

I'm no expert on growing herbs indoors (why I am visiting this forum today); this has just worked for me for some reason.

I kept my Rosemary in a 12 inch plastic pot for two years, outdoors spring through fall, indoors through winter. It did well under florescent light with plenty of water. Last winter it was too tall for my light table so I placed it on a cabinet near a window. It did poorly there for lack of light and it was also very potbound. In spring it was still alive so I planted it in-ground, where it gradually perked up nicely. I'm in zone 5 and I harvested a little today to season a roast chicken. We've briefly had temps as low as 15*F. I don't expect it to winter over, but Rosemary seems tough enough to give many months of service.