Mike,

What kind of GH do you have? Do you have some sort of thermostatically controlled ventilation already?

You are right, this is a challenging time of year. My experience is that you have to start ventilating once spring outside temps hit about 60F. I took the cover off of my exhaust fan and intake vents about two weeks ago and the fan was on and off all day today.

Personally, I find the most damage comes from removing my extra poly film in the spring. No matter how carefully and slowly I pull it down, even if I put up shade cloth, I still get some burn on things.

Can you not fix it so one window can open. Perhaps hinge the top so it can be lifted up and proped open or held open with a length of chain. Then you can staple screen to the inside. You really need cross ventilation in a greenhouse--north and south is best. Even a fan reversed to it blows the hot air outside will not cool it sufficiently on a hot day.

oilpainter,

That's what I intend to do after this week. I have two windows I can remove and replace with screens but currently they have plastic covering them on the outside. Inside I have IR/AC film over the walls and ceiling. It is suppose to get quite chilly for a couple of evenings (~35) then should warm up and stay mild enough until November!

Mike

Your idea about having removable coverings for your windows is close to what I do, this time of year. My GH has polycarbonate panels that clip and screw to the outside of the aluminum frame. I've made screens the same size to replace some of the panels during hot weather.

As you said, this time of year, it's too cold at night to leave the screens in place, but too hot during the day to leave all the panels in. Frustrating!

Fortunately, it only takes me a few minutes to remove a solid poly panel, lay it behind the GH (out of the wind) and put in a screen. Then I go out and put the panel back in place, late in the day, before night temps fall.

I do the same dance in the fall...! I will be happy when our night time temps get high enough so the screens can go in, and stay in!

Today may have been the most perfect day of the year. Very bright sun (45K lux this morning and higher during the day) but temps in the low to mid 70s with the door open. I moved 180 tomato seedlings into it yesterday so they should be having a banner day.

Mike

I have automatic fans and shutters for venting, but in quickly changing weather, or in weather with bright light, but cold outside temps, I over-ride it. I also have manual vents in the end walls. This give you a gentle, passive system whereby cold air is not sucked in or blown over tender young plants. Cold air doesn't rush in, hot air pushes out. The manual drop vents are on chains, so I can adjust just how much opening to allow some air exchange without setting off the heater stats.

We have details in another thread but we just cut and opening in our solar pool cover so one of our roof vents can open and close. This seems to be working well now for heat but we'll have to see how well it works next winter.

I have build transom windows above my doors. The inside frame has hardware cloth tack to it to stop birds. I simply open the windows on both ends. When it get warmer, I leave the front and back doors open and I have a large fan to move air.

We try to avoid manual processes as much as possible. As an example, last week when I left for work it was 22F outside and by 2PM it was 78F. Obviously we're not home during the transition so if I left a window open in the AM I'd risk the GH being too cold and if I left the windows closed we're be roasting our plants all afternoon.

I think ventilation is critical this time of year, but unless you're home all day every day, automatic/thermostatically controlled venting is a must.