Greenhouse Gardening In The Winter

Gardening in a harsh winter sounds challenging and intimidating. Indeed it is not an easy task. But still, people worldwide are successfully growing plants in negative degrees for a long time. 

Greenhouse gardening in the winter is famous for artificially trapping heat and growing greens. If you make a greenhouse accordingly and maintain a few rules, you can also successfully continue gardening even in the harshest of winter. 

Here is what you need to know to get started in greenhouse gardening in the winter.

Know Your Hardiness Zone

The first thing you need to know is where your location is on the globe and thus exactly what hardiness zone you are in. 

USDA plant hardiness zone map is a reliable resource to figure out your area’s hardiness zone if you are in the US. 

The online version of this map also supports zip codes of areas. 

Select The Greenhouse That Works

If you're able to, build a large-sized greenhouse in your available free space. It provides more flexibility and holds more crops. While choosing the location, make sure that the place gets a moderate amount of sun.

Position your greenhouse from north to south lengthwise. This position will allow the greenhouse to absorb more sunlight. More light will come from the south side than the north.

You have to consider that the places that might be sunny in the summer might not be as sunny in the winter. Unobstructed sunlight is necessary, especially if you are making an unheated greenhouse.

Make sure that the roof of your greenhouse has a moderate slope. It is crucial in winter because snow will accumulate on a flatter surface. A steeper surface allows the snow to fall off.

Excess snow poses a threat to the structure of the greenhouse by adding extra pressure. Also, it prevents the sunlight from entering. Make sure to sweep any snow off the roof.

The structure of the greenhouse should be made strong so it doesn't fall apart in rough weather. 

In winter, double layers of plastic will provide extra insulation. The layers are pumped in with a specially designed electric fan that inflates the layers.

It is important to remember that your already built-up greenhouse needs to be properly cleaned out before you plant winter crops in them. 

Soil For Greenhouse Gardening In The Winter

In winter, the soil condition is not the same as in summer. It is not only that the soil is cold but there is a lack of nitrogen and other nutrients in winter soil.

To compensate for lack of nitrogen during the winter months, it's necessary to add sufficient fertilizer to the soil. Organic fertilizers are always the best option.

Make sure that the soil has enough water but not excess water.  

What Type Of Crops To Grow In The Greenhouse?

There are many cold-hardy crops to grow in the winter. 

Choosing the best variety of seeds is the key to success with all crops. 

Choose the seed variant that is cold-hardy.

Here are some crops that thrive in winter.


If potatoes are planted in the late summer, then they can be harvested in the winter. 

It doesn't take much to protect potatoes from the winter.

With sufficient heat in the greenhouse and by choosing the right variety, you can get a good harvest.

Dark land, Norland, Belmondo, Adirondack blue, red gold, and Yukon gold are winter hardy potato variants. These potatoes are known to survive harsh winters.

If you want to grow your potatoes throughout the winter rather than harvesting them early, you have to plant a bit later. 

August is a good time to plant potatoes. Then they can be harvested during New Year.


Root vegetables such as carrots grow well in winter. At this time, the sugar production of this vegetable increases. 

Thus sweeter tasting root crops are produced. Similar crops are turnips and beets. 

Make sure to harvest carrots before spring comes. In spring, carrots grow flowers and become bitter-tasting.


Lettuce needs to be mature when the cold comes. It is best to germinate these at the end of summer or in early autumn.

It is possible to grow lettuce all winter long with a bit of care. The best-suited varieties are destiny, winter king, land cress, and winter purslane.


Spinach is another excellent option for winter. The varieties are Bloomsdale long-standing and viroflay.

It is crucial to give enough space between spinach plants. If spinaches are planted too closely, then they will stay wet, which can harm the crop in the longer run.

During winter, there is less nitrogen in the soil. So additional nutritional crops can be planted beforehand. Without enough fertilization, spinach leaves will grow small.


Kales are very cold-hardy and are known to survive temperatures of negative degrees naturally. 

Although kales can only grow properly with temperatures from 41-98 degrees Fahrenheit, it is quite easy to have such a temperature in a greenhouse.

Red Russian, scarlet kale, dwarf green curled, true Siberian, winter bore kale and dwarf blue curled kale are best for winter seasons. Kales need sufficient sunlight of 6-8 hours a day.

Though in a greenhouse with proper heating and fertilization, fewer hours of sunlight wouldn't hurt much. This makes kales and an excellent choice for greenhouse gardening in the winter.

Kales should be planted 5 millimeters deep into the soil. Planting multiple seeds together is a good strategy.

If you want a winter harvest, then late August is a good time to plant them, or you can plant them late in September to grow through most of the winter. 

Kale seeds germinate in 5-7 days. Kale can be harvested after 2 months or 2 and a half months from planting. 


Winter gardening is not limited to veggies. You can plant winter-hardy flowers such as viola, calendula, alyssum, pansies, and other variants. 

Flowers do require extra sunlight and heat control to bloom to their beauty. If you are a hobbyist, then you might want to take the challenge.


Onions are a very good choice for winter. They should be planted 2-4 inches deep with 6-10 inches separation in between each onion bulb. 

In the winter, the best onions for greenhouse gardening are white multiplier onions, yellow potato onions, Kentucky hills, and valenica.


Firstly, to plant peas, you need to set up the climbing structure for the peas, such as trellis or stakes with strings. Then it would be best if you planted the seeds in higher quantities.

Not all pea seeds germinate, so planting more is a safe bet. Peas must not be overwatered because they are very vulnerable to excess water.

Peas can be planted in winter. There is no need to germinate them beforehand as they can be placed directly into the garden soil.


Herbs are easier to grow compared to other plants. Rosemary, lavender, chives, parsley, thyme, basil, and oregano are common options.

Herbs don't need much watering and are very well suited for greenhouse gardening in the winter.


Cloves of garlic are planted during winter. They grow through the winter and when summer comes, it's harvesting time. When harvested, they are dried for two weeks and then stored. 

Garlic can be grown in greenhouses easily. They should be planted 3 inches deep and 4 inches apart. 


Tomatoes can be grown in greenhouses all year long. Though if it is too cold of an area, then additional heating may be required, increasing the cost of production.

Small-size variant tomatoes are best for winter gardening. Plant seeds 1/8 inch deep into the soil. The soil bed should be large enough to accommodate the roots.

Knowing When To Plant The Seeds

For most crops, they should be in mature form when winter hits. For that reason, plants should be planted early.

For some plants, late summer and for some late autumn is perfect to start planting. Check the longevity of your selected crop before you plant them.

Seeding time is directly connected with harvesting time. If you want to grow plants throughout the winter, then plant them in late September. 

If you want to harvest at the start of winter, the plantation should be done in late July. 

How To Stop Plants From Freezing In A Greenhouse?

Plants can freeze up even inside a greenhouse. The reasons are excess water and a low volume of soil.

If the plants are watered irregularly or too much, then excess water will freeze and harm the plants. Planting trees in small containers are another mistake. These small volumes of soil lose heat very fast thus freezes up.

Therefore, reduce watering in the winter because the plant's vascular system runs much slower and therefore doesn't require much water. This will reduce the chance of freezing.

 Also using large beds of soil for plantation will store more heat in the soil. 

When To Leave The Doors Open

Greenhouses are made to trap in the heat, but they are not meant to be kept closed at all times. There are necessities of keeping the doors open from time to time.

Firstly, plants need CO2 to grow. If the doors are kept closed at all times, then the plants will not get enough of it as the reserve is spent. Thus ventilation is necessary to let new air in.

Secondly, it can get too much heat in your greenhouse. Heat is just as bad as cold. You need to monitor the temperature inside your greenhouse.

If it is daytime and the temperature reaches above 45 degrees, it is best to keep the doors wide open. This will allow for a natural temperature balance. Temperature can differ from area to area.

Lastly, too much humidity will lead to condensation, which is not good for the plants. If the plants remain wet at all times, then they will not grow correctly. 

To control this, open the doors of the greenhouse when it starts to get too humid.

Adding vents with temperature sensors in the greenhouse is a good investment. 

How To Know If You Need To Use A Heater

You will need to use an additional heater for greenhouse gardening in the winter in case of two conditions. 

One is if you are in a zone that is too cold. And the other is if you do not get enough sunlight due to grey weather.

In both cases, you need to consider what type of heater to use. Heaters can improve plant production but will increase production costs. 

There are a few options to choose from:

1. Electric heaters are a comfortable option as they are easy to use. Though if you live in a region where electricity is highly-priced, this may not be the best option for you.

2. Another option is to use wood-burning heat. This will require manual labor and time. Though it is cheaper in some regions, it can be a bit tough to do for some urban areas.

3. You can also use a gas-based heater. This is costly and thus, you should only use it if the crop is highly profitable.

Passive Heating Methods That Don't Need A Heater

If you are not using any extra equipment for heating, there is no need to worry. For most parts, you can use these alternatives.

You can use black-colored water barrels. The water in these barrels absorbs excess heat from the greenhouse during the day and then at night slowly releases heat, which keeps the greenhouse warm at night.

This is excellent because it balances out the excess heat and the lack of heat. If you do not have black barrels, you can use normal barrels and paint them black.

Another idea is to raise the plant beds above the ground. This can be done by making the bed in raised structures or by hanging the soil bed structures from the ceiling. 

Final Words

Greenhouse gardening in the winter is undoubtedly more challenging than in other seasons. Properly knowing what to do and what to avoid can save time, energy, and money. 

By following the mentioned guidelines, you can grow greens even when it's all white outside. Remember, it's all about providing your plants with the desired environment.