I figure it may be useful to have a place to talk about how we set up greenhouses and use them.
I’m hoping to use mine for the first generation of perennials that are almost-but-not-quite hardy enough for my zone, and then plant their seeds outside the greenhouse in favorable microclimates, and then plant their seeds without any protection, to see if I can get some individuals that work well in my zone without any particular effort. A greenhouse is an excellent first step to get there.
Right now, my greenhouse setup includes:
One $160 greenhouse that I bought from Amazon. I plan to take off the plastic in summer, because I don’t need a greenhouse in summer, and I do want the greenhouse to last longer. We get high UV in summer, so if I leave the plastic on all summer, I expect it to be dead before fall. If I keep it on only in winter, it’ll probably last five years or more. It’s 13 x 10 feet, so it has 130 square feet of space.
Four IBC totes, each full of 250 gallons of water. One is inside the greenhouse. Three are outside the greenhouse, against the greenhouse’s north wall. I use these for rainwater capture, so they were empty at the beginning of winter. (We get almost all of our water in winter.) Right now, they’re at peak effectiveness. In October, they were empty and not worth very much. This means my greenhouse can hold in a lot more heat in spring than it can in fall.
Two rain barrels that hold 50 gallons of water each inside the greenhouse.
About 100 milk jugs filled with water, arranged around the north edge. Whenever we finish drinking all the milk in a jug, I fill it with greywater from our sink and take it outside to the greenhouse. That provides more thermal mass. Again, these accumulate throughout the winter, so there are none in the fall. (In summer, I empty the jugs out to water my plants and recycle the jugs. Their number 2 plastic will crumble within a month of our summer UV, so I only use them for one winter. Soda bottles are much better, if you have those available.)
A bunch of sheets of UV-resistant greenhouse plastic from my attempts to make DIY greenhouses last year. (I wound up buying one primarily because that metal frame looked much sturdier than anything I had come up with.) I am using those sheets as an extra liner of greenhouse plastic, to increase the insulation, so less cold will escape at night. I bought 20 of these clips, which work perfectly to hold multiple sheets of thick plastic around a metal bar without falling off. (I tried several other types of clips, too, and those weren’t good enough.)
Those are the important things. Here are a few more things I’ve added.
This solar-powered light, which comes on automatically at dusk and stays on until nearly dawn. It’s not a lot of extra light, but it’s a little, and I’m thinking it will help transplants grow faster. Plus, it’s convenient to be able to see if I want to visit the greenhouse at night.
This thermometer, which tells me what temperature it is in the greenhouse at any time, without having to leave the comfort of my house. It also keeps a record of historical highs and lows. I figure that’s exactly what I need to get a sense of what I can get away with growing out there.
This solar panel outside the greenhouse, with its cord heading under the greenhouse plastic to go inside the greenhouse. This power bank hooks up to it. The solar panel can handle being wet; the power bank can’t always. So I figure it’s smart to use the greenhouse to keep the power bank dry.
This is in progress; I just bought these things, and they haven’t arrived yet. I’m hoping this idea will work. I bought this thermostatically controlled outlet,this ceramic heat emitter, and this clamp lamp. After the power bank has been charged during the day, I plan to plug those into it at night. If the temperature dips below 32 degrees, the ceramic heat emitters should turn on and stay on for about an hour and a half before draining the battery. That won’t make a huge heat difference, but it should be a) safe, b) cheap, and c) powered entirely by renewable energy. I figure that may make a 1 or 2 degree difference on the coldest nights, and that can be game-changing.
Our greenhouse is against a north-facing (we’re southern hemisphere) compressed earth brick wall. The frame is from a few trampolines bought at the waste transfer station in town. It’s covered in greenhouse film.
In we have an old bath tub as a pond, four citrus, a curry leaf tree and some aloe vera which would not survive our winters outside, along with a few other bits and pieces. In winter we put our summer sown seedling tree stock in there to grow on for planting out late spring. It stays reasonably warm in winter. Last winter for example when it dropped to -12°C (~10°F) outside it was -3°C (~27°F) in the greenhouse. We’re at 30° south latitude so we have pretty good winter light levels (think Houston Tx).
It does get hot, like all greenhouses. There are doors at each end, vents along the bottom and vents in the ‘roof’. There are also windows in the wall it’s attached to which open into a shed. Even with all these open it gets hot - 25°C (mid 70s Fahrenheit) outside means well over 30°C (~86°F) inside.
Mine gets well over 100 on sunny days if I don’t open it up, which can cook the plants within (I saw that happen in fall!). When I had less thermal mass, and wasn’t in the habit of opening it every morning, it would regularly get up to 115 or more. Yipe! So now I’ve tried to cultivate the habit of opening it up every morning. The only exception is on very cold days when it’s very cloudy – then it’s okay (and usually a good idea) to leave it closed all day.
For me, I’ve found that if the temperatures stay below 40 during the day, and it’s heavily overcast (often the same thing), I can leave it closed all day. If it’s sunny, which it is at least three-quarters of the time, the afternoon temperatures are generally above 50, so it needs to be opened before then.
I tend to open it around 9am to 11am. Sometimes I forget until around noon to 1pm, and it’s usually over 90 within, but the plants are still okay.
Figuring out when to close it can be tricky. I’ve defaulted to around 6pm. I could probably keep in more warmth if I closed it around 4pm, but I’m concerned that it would get too hot in the last few hours before the sun goes down, if I closed it that early.
Mine comes with an unzippable door, which is what I leave open. There are velcroable vents on the sides, but I can’t be bothered to use them. They’re too low down to really let the heat out, anyway – the door unzips all the way to the top, and that is what’s needed to let the excess of heat escape.
I use this small greenhouse for now, planing to get a bigger one later. I put shelves on the inside to hold more seed trays. The plastic cover has resisted my very hot summer pretty intact. I can not say the same for the wind. I do not go to the garden every day, so I open and close the door every day is not feasible for me. In the same way I can not water it every day, so the seedlings suffer a bit. In summer I just leave the door open, in winter I just leave the door closed. Leaving the door open at night is not the best for summer but having the door open in the day is the only option in summer. I only got one opening, a door at the frond and that is it.
I was thinking to upscale to a low tunnel, putting up plastic in winter and shade cloth in summer. I guess when I give my tree nursery a push.
I think I cooked my tomato seedlings last year in it. The others plants were totally fine. So now I leave the door open in summer.
I more or less gave up on greenhouses after several failed experiments; here in Colorado, the sun is so intense that even on a fairly cool day and with vents open they can overheat. In this climate, a heavy-duty ventilation system seems like it would be necessary. I had a lot more luck with spun-bond row-cover over hoops, since it is self-venting; those covers allowed me to grow lots of things that wouldn’t normally grow well here (though they won’t help much for perennials). But they tended to be damaged by the wind, and replacing them all the time wasn’t very sustainable.
In the long run, I’m hoping that landracing will make it possible to grow most things without any protection; maybe someday I will build a “real” greenhouse with a mechanical thermal battery for some tropical plants.
Definitely. My biggest hope with my greenhouse is to use it as an in-between step towards adapting perennials I want to be able to survive my winters without help.
Meanwhile, since I have it, obviously I’m gonna use it for other purposes, as well . . . because why not?
One of my hopes for this year is to plant runner beans in my greenhouse. This seems ideal for three reasons.
They don’t seem to want to set pods in my summer heat, so if I can sow them safely a month or so sooner, that may make a difference between them producing or not.
They’re perennial in zone 8, and I’m in zone 7. So if I plant them in the ground in my greenhouse, I can just leave them through the winter and see which survive and come back in the spring. If it’s all of them, awesome! If it’s only some of them, also awesome!
Once I remove the plastic from the greenhouse in summer, I’ll have this really solid metal frame that begs to be used as a bean trellis. That may make it a bit more complicated to put the plastic back on in fall, but it will also make it more rewarding, because I’ll get an extra month of cool-weather growing of the runner beans in fall, too.
