Fresh grown lettuce, peas, broccoli and carrots when you’re bundled up and there’s white stuff on the ground? Why, yes! I never thought it was possible until I had the opportunity to give gardening a go in my Palram Snap & Grow 6×8 Silver Greenhouse these past few years during winter and early spring. I learned a lot during my cold weather gardening ventures and have a few tips I’d like to share with you.
In order to be successful in greenhouse gardening during the months that make you say “brrrrrr,” you need to first ask yourself some very important questions.
A lot of greenhouse gardening concerns revolve around temperature. This is true whether you are gardening in the middle of summer or in the throes of winter. For winter and early spring gardening, however, the first thing you need to decide is whether or not you will be heating your greenhouse. I opted to keep my Palram greenhouse unheated. There are electric heat options as well as propane and paraffin heat solutions available that you can consider. As you surely know, heat has a price tag attached, so this may pack a wallop on your wallet, especially if you live in an area with a long winter season. You will need to consider if the output of your garden greenhouse will be worth the expense of heating it, so you may want to open an Excel spreadsheet and crunch some numbers. For many, however, the heat required to grow warm season crops such as fresh tomatoes, peppers and beans is simply priceless.
The decision on greenhouse heating will naturally impact the choice of plants you can grow. If you opt for your greenhouse to remain unheated during the colder months, your window of choices is reduced to cool season crops only. This brings up the question “What is the difference between cool season crops and warm season crops?” Cool season crops do best when temperatures stay below 70°F. (21 C.) during the day and above 40°F. (4 C.) at night. Warm season crops, in contrast, grow best above 70°F, with care not to let temperatures dip below 50°F. (10 C.).
Many mature cool season plant varieties, however, can withstand temperatures that are much colder (even freezing temps) and can tolerate light to moderate frosts; however, seed germination for cold season crops happens only in soil temperature ranging from 40 to 45°F. (4-7 C.). The catalog of cool season crop choices is quite large and includes hardy root vegetables, such as carrots, and leafy greens like spinach and collards, just to name a few. If you plan to grow cool season crops in an unheated greenhouse, you will need to do your research, especially when you are window shopping in your seed catalogues. Pay close attention to the fine print, and especially note the cold tolerance of each variety. Choose varieties that have a higher threshold for the cold, and even shorter windows of time for maturity, to give yourself a better chance of success in your cold weather gardening venture.
Whether you grow cool or warm season crops, you will need to monitor temperature, and even humidity very closely on a daily basis. Installing a thermometer and hygrometer inside your greenhouse to measure temperature and humidity is highly recommended. In fact, you may want to invest in thermometers and hygrometers models that are Wi-Fi capable, which allow you to take your readings anywhere via your smart phone. Monitoring these readings will give you clues on how and when to tweak the greenhouse environment, whether it’s facilitating more air flow or cooling/heating things down.
Winter gardening is challenging in a greenhouse. Be prepared for some ups and downs. You may not knock it out of the park the first time, but with some trial and error, you’ll learn the ropes relatively quickly. One last tip – keep a garden journal to record your experiences; you’ll find these insights you record to be invaluable as you grow as a greenhouse gardener.