My greenhouse is so humid
 

After years of growing in the house I finally got a greenhouse. I've had plants in there for about a month.

I'm using little Govee sensors to monitor the the temp and humidity. The humidity varies of course based on the temperature and it ranges between 25% to 97% with the average somewhere around 85%.

Overall the orchids seem to love it and I'm seeing a lot of new roots -- especially on the bark-mounted ones.

Do these numbers seem right to y'all? Specifically I feel it is maybe a little too humid and that there might be fungus or other leaf troubles down the road. I do have circulation fans going round the clock and can see nice gentle sways from most of the leaves.

I prefer not going over 80% in my semi-enclosed sunroom due to fungus issues. There are orchids that want to be over 80%, but I don't have many of those. I'm surprised yours goes down to 25%. Do you control air exchange/vents manually? I would prefer not going below 50%. I manually open or close doors. I have an automatic sprayer that runs for a few minutes shortly after dawn. I use a portable evaporative cooler for cooling and/or humidification. I store 300+ gallons of water in barrels in the sunroom to maintain winter night temperatures without a heater. But on a few very cold nights I open the doors to my house so the central system can keep the room warmer. Humidity drops very low on those nights, but my plants tolerate that occasionally.

I ran into trouble after elective surgery during hot weather. I knew I wouldn't be able to water adequately for some weeks, so I closed the doors and ran the evaporative cooler constantly. It was too hot and humid in my sunroom, and I lost plants to Erwinia infection.

Your biggest problem will probably be adequate air exchange during cold weather. It's tempting to save heating money by closing the vents. But very high humidity combined with too-cool temperatures can cause a lot of disease problems.

Currently the sensors are reporting 77 degrees and 88% humidity. The sensors are close to the the glazing, so perhaps they are reporting a bit higher than the air in the middle. I'll move one into the middle and see if that changes things any. But yeah that just seems a bit high to me. Thanks for confirming that you like to keep it under 80%.

We are having some freakishly hot and dry weather for October in Oregon. Since July we've had less than 1/2" of rain. I currently have an exhaust system on a thermostat which kicks on at about 85 and draws lots of dry outside air through to cool. That is when the humidity drops to the low, but it rebounds pretty quickly once the temp drops and the exhaust fan shuts off.

I'm not so worried about the low because it doesn't spend that much time there. And we're about to move into a more humid and cooler outdoors. For next summer I do have a fogger that I plan to hook up to a thermostat and have come on just before the exhaust fans start. That should help even the low humidity during the hottest parts of the day.

Since this is a new greenhouse I haven't worked out water storage for thermal mass yet. That is in the plans for next year.

I have a 22k btu natural gas furnace that has done a good job on our (so far) coldest nights.

I didn't put any always open vents through the wall. D'oh! That is probably what I need to do.

What’s the size of your greenhouse? The smaller the greenhouse, the harder it is to maintain interior conditions and the larger the swings will be. The 40x60’ greenhouse at my last job was much easier to keep humidity and temperatures where we wanted than the 10x16’ we grew starts in.

My greenhouse in PA was routinely in the 90%+ range. The plants loved it.

@Dimples - It is on the small side 11 x 15 feet with the short side being 8' and then up to 10' on the tall side. All that there was space (and budget) for. And I'm okay with the swings for now, but I was feeling the average humidity was too high.

@Ray - good to know that it can be that high. And the roots and blooms (So far I've had 4 buds not blasting from the move) would agree that they like the conditions.

I'm feeling good about the air circulation which seems to really be mixing it up, and I figure that is key to prevent fungus/rot with the high humidity.

Thanks everybody for the thoughts.

In a humid location where there is a significant temperature drop at night, the air outside will often be saturated to 99/100% relative humidity in the early morning hours. I don't grow orchids in my greenhouse or measure humidity in there (or heat it), but I suspect it would take quite a bit of heating to avoid getting into that high 90s range, if it would even be possible.

For a few hours it's not a problem. I don't want it that high on a regular basis. Others disagree.

I have a small (8' x 10') greenhouse. I don't know the humidity since I don't measure it, but when it's cool outside, it stays pretty wet... so I have to guess that it's in the high 80's or more. But air movement is good and there is air exchange. (It isn't airtight... which is fine for southern California, would be problematical in a truly cold climate) I haven't had any problem with fungus/mold/etc. The air exchange probably saves the day.

Can you send a picture or two of the greenhouse? I would like to see it. Thanks.