Last Updated on June 12, 2023 by Real Men Sow
A greenhouse is a valuable asset for any garden. It can make the growing season longer, protect plants when they are at their most vulnerable, and give gardeners more options. Your location, the size of your greenhouse, and your gardening goals will determine which plants you can grow in your greenhouse during winter.
What To Expect With A Winter Garden
It is important to remember that plants won’t grow as fast in the summer. Depending on where you live, the days it takes to reach maturity for each vegetable can double. Some plants might not reach full maturity, but they will still be edible.
Some plants won’t make much progress for a few weeks, but as long as they don’t die, they will grow again as soon as temperatures rise enough. There will be little or no growth in December and January. Don’t panic! This is normal. Just be patient. They will thrive once the days get longer and the temperatures rise.
Greenhouse During Winter: Tools For Success
Winter greenhouse gardening is an entirely different experience than any other season. You need to be very specific about what you want to grow in a cold climate. You may have to modify your greenhouse if there isn’t much light or heat in January and February.
How To Keep the Heat In
Passive solar plastic bottles can be used to heat the greenhouse without electricity. Fill plastic bottles with water and paint them black. The black paint will absorb the heat from the sun during the day. The greenhouse will heat up at night as the stored energy from the sun is released. These can be placed around your aluminum or wood greenhouse to get the best results.
Fan heaters circulate heat and air. Thermostats can also be used to control the temperature. Many thermostats can also be set to automatically turn on when the temperature falls below a certain level. Temperatures around 2C are sufficient to keep frost away, and most plants will survive.
To keep the roots of the plant warm, electric heating pads can be placed under a container. This heating method is less effective than other methods, such as fans. It can be costly depending on how much you use it for. They are portable and have a direct heat transfer. While seed-starting heat mats work well, regular heating pads for sore muscles are also a good option.
To reduce heat loss and increase the temperature of plants, you can cover them with fabric row covers. This is particularly important for seedlings, which are more fragile. Straw bales can be placed around the greenhouse to help keep heat in. Although it doesn’t provide additional heat, it can reduce heat loss, which can be very beneficial for your vegetable survival.
Regular packing bubble wrap is a great insulation. You can wrap it around the greenhouse’s walls and frame. To keep roots warm, it can be wrapped around individual pots.
It may be necessary for plants to have sufficient sunlight during months with low levels of sun. It will all depend on what you grow and how long it is winter there.
Choose Proper Seed Varieties
There are many varieties of seeds for every type of vegetable. You should look for varieties that can withstand cold and have shorter growing seasons.
Plant in Pots
Sow seeds in the pots that they will be living in, so transplanting is not necessary. Transplanting plants is stressful and they already have to deal with the stress of colder temperatures so it is better not to do this.
Planning is Essential
You will need to select crops that are similar in needs if you only have one greenhouse. It is difficult to keep different conditions in the same space. A uniform environment will make it easier to grow and be more successful.
Greenhouse During Winter: Planting
Cabbage & Broccoli
These cold-season vegetables require a temperature of 45–55°F at night and 50–70°F during daylight. They are more susceptible to heat stress than they are to growing. For spring planting, they are best planted in the greenhouse in mid-late winter. If the greenhouse is heated properly, it can grow all winter.
You can plant potatoes in large plastic buckets or thick plastic grow bags. They will be ready for harvest by March if they are planted in January. A crop that was started in February can be kept in any greenhouse until it reaches maturity. If the weather is suitable, the plants can be moved outdoors and harvested at the beginning of April. Frost can be devastating to potatoes so keep them warm by covering or heating your greenhouse.
They can be planted in the fall and harvested once the ground thaws. Check the carrots if you have a warm winter with the ground still thawing once or twice before spring. They might be ready. This is where the variety of carrots can make a big difference. Make sure to get one that is extremely cold-hardy.
Lettuce and Greens
Lettuce, and other greens, are fast-growing and prefer cooler temperatures. Some are resistant to frost. Make sure to check your seed catalog to find the best varieties. These seeds should be planted in the greenhouse in autumn. As the outside temperatures drop, they will thrive in the greenhouse. You should harvest the leaves as soon they reach maturity; do not wait until they become fully mature.
Plant a variety of greens and lettuce to get the best results. There are many to choose from, and each variety has different maturities and requirements.
You will harvest cool-weather spinach almost every winter if you plant successive sows. It can slow down sometimes, but it will rebound once temperatures rise again. It is a great greenhouse vegetable because it grows fast when the temperature is right.
Depending on the variety, cold-hardy vegetables can survive temperatures as low as -6°C. If it gets below that temperature, it will require heat to keep it going or wait until outside temperatures rise so it can start growing again. You can grow kale year round by planting several crops. Bonus: Kale grown in winter tastes sweeter, as it produces sugar to protect its cells.
Garlic can be planted in January and transplanted when the soil is ready. You can also keep them in pots, and move them outside when it is warm. Choose a hard neck variety and not a softneck because they are cold-hardy.
All cold-hardy plants, including coriander, leaf celery and parsley, can be grown in a greenhouse during winter. You can start them in the late fall and keep fresh herbs all through winter. Although their growth may slow down during particularly cold or dark days, it will increase when the temperatures rise and the days get longer.
Vegetables To Start In The Greenhouse During Winter
Tomatoes are the most popular vegetable that is grown in greenhouses. They grow for a long time so starting seeds in the greenhouse will give them a head start. The tomato seeds should be planted in the greenhouse for at least 4-6 weeks before being transplanted outdoors.
Night temperatures should be at least 55°F. To ensure that the greenhouse is warm enough to grow tomatoes, you should monitor the temperature. The plants require lots of light so the greenhouse should be placed in full sun.
There are many pepper varieties, including bell peppers and hot peppers. All will thrive in a greenhouse. They require nighttime temperatures of 55°F. You can start peppers in the greenhouse, and then transplant them outdoors. They can also be grown indoors all year if the temperature remains high enough.
Peas can be started in the late winter and will be ready to plant in the spring. Peas planted outdoors when the ground is not able to be worked give them an advantage. With peas, you’ll be the talk of the town for weeks!
In late winter or early spring, start cucumber seeds in your greenhouse. It is important to plan the timing so that they can be transplanted when the temperature outside is above 70°F.
Squash, like cucumbers, benefits from being grown in a greenhouse. They can then be transplanted outside as soon as the weather is warm enough. Many squash varieties will not mature in short-season areas without this extra growing time.
To mature, this vegetable plant takes approximately 2 months. Okra requires a minimum of 65°F soil temperature. Okra can only be grown in cooler climates. It cannot be planted outside until the spring, so it is difficult to grow in regular seasons. It is a great idea to get the seeds started in the greenhouse early.