Low-tech Greenhouse Ventilation
dding a greenhouse to the garden mix requires a little more management than a regular garden. Our greenhouses are unheated, so the nighttime temperatures are about the same as outside. So that means covering tender starts or providing a little bottom heat in addition to the covers on these frosty nights. That’s pretty easy peasy. Keeping the plants cool enough is more of a chore on most days. Cloudy days are not a problem, but days like yesterday when the mercury reached 70°F outside, quickly become worrisome to baby plants, and cool weather crops we have planted for our inside garden.
We solved a lot of the heating problems by orienting our greenhouses on a north/south axis instead of east/west. I’m growing plants in these houses during the growing season, so I want as much sun as I can get and not oppressive heat. Winter heat collection is not what I’m looking for. If you want a winter greenhouse, orient your building east/west. This a subject fraught with much heated discussion in growing circles…it really makes no difference to me how someone else orients their greenhouses, I’ll stick with my method as it works for me. Any greenhouse is better than none, IMHO, and gives a gardener more opportunities to grow food.
Here is a nice diagram from The New Garden Encyclopedia: Victory Garden Edition (1943.) It explains the north/south axis for the growing season.
With proper ventilation we can safely grow plants that like cooler temperatures as well as heat loving crops like tomatoes, peppers and melons in our greenhouses.
I could grow these crops outside, but I can never be sure if we will get the weather to ripen enough to tomatoes to preserve or eat anything but green tomatoes and peppers. I’ve probably mentioned this before, but growing up here in the Cascade foothills, as a kid I had never seen a ripe or colored pepper come out of anyone’s garden. All peppers were green :) I love green peppers, but ripe is wonderful.
Disease and insect pressure is a consideration too, I don’t have to worry about late blight ruining a whole summer’s worth of work with my tomatoes. Some years we get an outside tomato year, many years we don’t. Also having a well-ventilated hoophouse doesn’t allow too many pests to set up shop. Of course, we get the garden variety pests like root maggots, flea beetles and cabbage moths, but they’re outside too, so I expect that.
Hot air rises, so gable vents on each end allow the heat to dissipate without needing electricity for a fan to move the air. Air circulation is huge with plants.
In keeping with our slow food philosophy we manage the vents by hand, instead of relying on technology. The vents are hinged and attached to a rope with a knot in the rope to stop the vent from opening all the way and breaking the hinge, just in case the rope slips out of your hand
Our greenhouses also have roll-up sides which work perfect for good air circulation. These photos were from yesterday, sides partway up to allow for some cooling , but not too much in order to keep the warm weather plant starts happy. I can roll up one side, both sides, just a few inches, or up to the hip board on really hot days. As with all things gardening, the weather dictates what you will do.
Low tech predator control is great too. Deer and rabbits love to get in the greenhouse. With chicken wire on the sides, we can open the house up for ventilation while keeping the personnel doors closed to keep varmints out.
Keep in mind when planning your greenhouse, your bells and whistles may be different than ours. My main job is growing and preserving our food, so I am home and able to pay close attention to our greenhouse needs. These ideas may not work for you, but low-tech solutions can be a money saver when designing your greenhouse.