Greenhouse Management Winter
Winter is the time when you want to really take advantage of your greenhouse. In my opinion the winter is an easier time to manage your greenhouse than the early spring. You do still have to pay attention to the temperature, humidity, ventilation, watering needs, and pests.
In the summertime I only use the greenhouse to dry herbs and seed. To transition to my winter greenhouse setup, I do need to complete a few tasks. I take the shade tarp off the greenhouse, fill up my black trash cans with water, install my hose and watering wand, and I install my electric heater with my setback thermostat. I am then ready to plant my winter produce.
In the winter, I am only growing cool season plants. For your cool season plants like lettuce, spinach, radish, peas, arugula, broccoli, and cauliflower, they prefer 50’s and 60’s during the day, and 40’s and 50’s at night. These plants can even tolerate mid 30’s at night, just don’t let them freeze. I try to keep it simple, so I have an electric heater that is attached to a thermostat, so it only kicks on when the temperatures in the greenhouse dip below 40. This keeps all my plants alive, and doesn’t waste too much electricity. I also have (2) 50 gallon black trash cans filled with water to help soak up the sun during the day and release the stored heat at night, lessening my electricity use, and adding valuable humidity.
Most plants prefer humidity levels in the 50-60% range. This can be difficult to maintain. One way would be to install misters set to a humidistat. I have not done that to this point. I manage it the old fashioned way, by watering as needed. I do have a humidistat that I watch, but it is pretty obvious when it is too dry. In the winter when it is cold and cloudy out, it is easy to maintain a high humidity. Sometimes I can go every other or even every three days between watering. My (2) 50 gallon trash cans that are filled with water also help a little to keep the humidity up.
When it gets really warm or if the air is stagnant, ventilation is a good idea. I have vents on top of my greenhouse that are filled with a gas that raises the vents as the greenhouse heats up during the day, and shuts them as they cool off. These vents are sufficient for the winter. In the spring I have to get a little more creative.
It is necessary to have a water source in the greenhouse. It will get old really quickly if you are filling up watering cans. Also, if you are heating the greenhouse in the winter, you don’t have to worry about your hose freezing. I have a hose bib that I water the plants directly from. I use a nozzle that allows misting and gentle showers so as not to blow out delicate seedlings. In the spring when it is sunny I am watering twice a day, giving the plants a thorough soaking. If it is cloudy and rainy out and my soil in pots are still damp, I may not water at all.
If you are using sterile potting soil, chances are your pest pressures will be minimal, but if you are using compost from your garden, you may end up bringing pests into the greenhouse. The problem with this is that their natural predators may not be present inside, so you may end up with a serious insect infestation. I do use compost from my garden, because I like my seedling to grow in the soil they will be transplanted into, and it is cheaper. So I monitor my plants closely for pests. If I can just put plants outside or pick the pests off by hand, I will do that. In some rare cases, I will spray a neem oil.