Mildew problems in my greenhouse during winter - any advice?

Hi everyone. I have a cold greenhouse that came along with my current home. It's a very basic glass greenhouse without any fancy climate control, heating, ventilation, lights and such but it serves it's purpose very well. I have a small electric fan heater that I use to keep it frostfree from March until the danger of frost passes so I can grow my seedlings out there. I also grow a few roses in there and overwinter some of the perennials raised from seed that I can't fit in my coldframe. The problem is that during the winter we frequently get rainy spells with temps just above freezing so the humitiy gets very high and mildew thrives. I've lost a lot of small plants to rot and my question is how can I prevent it? I just stripped the leaves off all the roses - they were all moldy and some of the stems had turned to mush. Any help would be greatly appreciated.

rannveig

Hi Rannveig

Do you know how high your humidity is? Generally you'll want it under 90% RH, better yet under 85%. Getting the humidity down generally means ventilating and (sometimes) reheating. The warmer inside air holds more moisture. If you push it out, the outside air you draw in will hold less moisture. Obviously if that air is too cold, you may have to reheat it.

Another thought, if you have an attached greenhouse, is to consider circulating the air between the house and greenhouse. In most cases, the house air will be drier. The GH could benefit from drier house air and the house could benefit from moister air from the greenhouse.

I have found this and the related links very useful: http://www.hortnet.co.nz/publications/science/n/neder/humid03.htm#top

Thanks for the link SB. The greenhouse is not attached to the house. I don't know what the humitidy is in there - I think my humidity meter is inaccurate. It's below freezing outside at the moment so it's not a problem right now but last week and the week before that were very damp with temps in the 40's and that's not good. Don't I need to disinfect the greenhouse somehow to get rid of the spores or is it enough to get the humidity down ? My worry is that if I cranck the heater up to dry the air that it'll get too warm inside and things will start to grow too soon .....

I think that to fix the problem in the future I'll need to install proper heating with hot water, it definately needs some heating to dry the air when it's damp.

Thanks so much for your advice :-)
Rannveig

You need to get some air moving. You need a fan, vents to circulate in and outside besides heat. Getting air movement is the most important. So get a fan and run it at least every so often.
Carol

Thanks Carol - I'll have to check into that .... :-)

I agree with the fan idea. Moving air is very important even without mold and mildew, but the moving air will certainly help those problems too. Everywhere there are plants there should be air moving. Small leaves should be visibly moving while the fan(s) are running. Run them as much as possible. If you don't want to run 24/7, then buy a digital programmable timer and have it run at least 10 min out of each hour. Heat would certainly help too.

And even if you have no rot/mildew/mold, you'll have stronger, healthier plants if they are grown with air movement.

Thank you so much for your advice - I'll have to go look for a fan :-)