Tell me about greenhouses

I can talk my missus into letting me have a greenhouse, but I should probably keep it in the 8ft x 10ft range or smaller for now. Depending on where I put it, I can give it 5 – 10 hours of direct sunlight. I’m in Denver-ish, so latitude is about 39°. Stuff I’m interested in growing is herbs, tomatoes, strawberries, peppers, and some salad veggies. I’m cool with trial and error learning, but advice & experience/tips is always welcome. What am I likely not thinking about? Is glass better than polycarbonate, or is there even a difference?

Polycarbonate isn’t not nearly as prone to breaking/shattering as glass is. I think glass might transmit more light.

If you want to grow year round you might need some supplemental gro-lights in the darkest part of the year.

Salad vegees should do with relatively low light and cooler temperatures. They might be good to start with if you’re planting right now.

Peppers and tomatoes grown indoors need support. The stems don’t develop the strength they would when grown outside because you don’t have wind bending them every which way, stimulating the plant stem to strengthen. You might mitigate this somewhat with an oscillating fan.

Are you planning to plant in dirt or use hydroponics?

Dirt at first while I learn the peculiarities of the contraption. Longer term vision is to have a koi pond nearby and circulate their water through the garden as part of an aquaponics setup.

8x10 should be sufficient space for you to add in hydroponics on your way to aquaponics as an educational experiment.

Polycarbonate transmits plenty enough light to ripen, say, tomatoes, though. Multiwall polycarbonate has a tiny bit of R value; not much.

Greenhouse plastic (not polycarbonate) would need replacing every two to four years. Glass covered greenhouses are becoming rare, though you can probably still find them in hobby sizes.

Presuming that you need it to hold heat at night, you’ll need either a heating setup, or some form of insulating setup, or both; at least, if you want to significantly extend your season for tomatoes and peppers. Some frost-hardy crops will do well in an unheated greenhouse even in cold weather; but growth will pretty much stop during the Persephone period (less than 10 hours of daylight.)

In the summer, you may need some shadecloth or other shade, depending on how good your ventilation is, what time of day the shade hits, etc. I’d go for the location with more direct sunlight, and use shadecloth if necessary; it’s easier to cut your light than to create it.

Temperatures needed for germination are often a narrower range than those needed for survival/growth; and vary considerably by crop.

– Dirt in pots, or in the ground?

Pots. This rig is most likely going to live on a low traffic part of the deck, about 8 feet above the ground. I’m planning on giving it a floor (screw the structure to some plywood) to minimize bug access. Which leads me to questions about chemical-free pest control. Japanese beetles have moved in to the neighborhood.

Don’t forget about pollination for those plants that are not self pollinating.

The usual control for Japanese beetle is milky spore, which attacks the grubs in the ground. You might need to get people to apply it over large chunks of the neighborhood, though; and it’s not a quick fix. There are some tachinid flies that parasitize adult beetles; but I’m not sure whether they’re available to buy, or whether they’ve managed to spread themselves to Denver yet.

Greenhouse pest control in general can be tricky. I haven’t had much problem with it in a small greenhouse used mostly for growing transplants, and would have to do some research on this one. But bear in mind that anything you’re using is being applied in a confined space, and also that most even of organic controls that will work on adult beetles are relatively broad spectrum and may also hurt your beneficials.

– some sites seem to be recommending hand picking for small-scale setups; knock them off into soapy water and drown them in it. Check if they’re parasitized first.

A greenhouse placed on an elevated deck is going to sacrifice the insulation that a greenhouse anchored to the ground will have. The deck will need to support the extra weight, and the greenhouse may be less stable in high winds.

I’ve been researching greenhouses since before Covid, and have been struck by how flimsy many kit models seem to be, especially in lower price ranges. Despite what ads says, you’ll generally need at least two handy people to set one up.

Other thoughts: maximize the available sunlight. Get the largest one you can fit in/afford. A lot of people report that they wished they had gone larger in the beginning.

The community garden my mom is active in put in a greenhouse several years ago. They did an extremely good job with the passive heating aspect of it: Even in the dead of a Cleveland winter (back when we still got those), it never went below 55 F. But the biggest difficulty they had was providing the plants with enough carbon dioxide: It was so well-sealed that the plants were depleting what was in there. Ironically, the project was co-sponsored by a local brewery, and they could have had all the carbon dioxide they needed if they had sited it at the brewery.

Yours might not be so well-sealed, and connecting it to a koi pond might help with that problem. But it’s something that can happen.

A friend of ours raises orchids as a hobby. The home he owns was purchased specifically because it once was part of a commercial greenhouse business. He tore down many of the buildings as part of his remodeling project, but kept a massive greenhouse.

His yearly heating/ventilation costs for the greenhouse exceeds what he spends on his modest home, but he is happy.

About a half mile down the road from our house is a CBD research and production facility with multiple large greenhouses. They are apparently shutting down or moving, since the property just went on the market.

It sounds like a great facility for me to expand into, but for some reason Mrs. J. isn’t hot on the idea…

A neighbor of mine has been scrounging around collecting old window sashes to build a greenhouse in his back yard. He contacted all the local window replacement businesses.

I think that it is very common for commercial greenhouse owners to pump in extra CO2 into the greenhouse to help the plants grow better.

Actually, even small cannabis growers have played around with supplemental CO2 (see: HighTimes, etc).