If you’re someone who has a true greenhouse in their yard, thousands of gardening enthusiasts around the world envy you. Greenhouses do a lot more than help extend the growing season, and the best greenhouse for winter allows you to shield your tender plants from cold damage. They are an excellent space to allow you to get exact climate control for a broad range of plants all year-round.
Also, your greenhouse for winter can give you the opportunity to have a positive influence on the growth cycle of your plants, and you can use it to have blooms even in the coldest months. If the idea of having a garden all year-round is appealing, then you want to know all there is to know about a greenhouse for winter, and we’ll guide you below.
When most people picture greenhouses, they think of structures that are active during spring and summer, but it’s possible to have a greenhouse for winter too.
Defining a Greenhouse
When you picture a greenhouse, if you’re thinking of something that involves buying a kit that comes in a box and you have to wrap it in plastic, you’re thinking of a cold frame greenhouse. So, it’s important to know the exact definition of a greenhouse in order to highlight how you can use it throughout the winter.
A greenhouse can be a cool house or a hothouse, or both depending on how you want to use it throughout the year. A hothouse has to keep temperatures at a minimum of 55-degrees Fahrenheit at night or higher, and a cool house has a minimum temperature of 45-degrees Fahrenheit at night. The maximum temperature usually sits around 90-degrees Fahrenheit during the day, all year-round.
To keep this temperature range, you have to be able to heat your greenhouse for winter according to the size, and you’ll want to heat to vent through the season. Greenhouses also use solar heat in many areas to keep the space warm as the design gives you plenty of opportunity for sunlight to stream through both opaque and clear glass or plexiglass-style panes. In many instances, you may also install a shade to draw across the top of your greenhouse to block out strong light and keep the plants cooler in the warmer months.
Cold Frame vs. Greenhouse
Taking into account how we outlined the definition of a greenhouse earlier, a cold frame structure is one that helps to extend your growing season beyond and after your seasonal frost warnings. These greenhouses can come in a large range of shapes and sizes, and they’re a great helping hand for gardeners who want to harness the sun’s energy and heat to get the plants started earlier in the season and to extend your harvest time.
In general, these are usually not a year-round greenhouse for winter, and it’s not heated. You can use them in warmer planting zones that have a lot of sun during the winter and lower instances of temperatures dipping below freezing. But, in these climates, these structures aren’t consider a true greenhouse for winter, even if they do work similarly.
Basic Winter Accessories You’ll Need
If the plan is to keep gardening well into the winter months, you’ll need to invest in a greenhouse with the proper insulation. A few pieces of equipment and accessories you’ll need to get started on your greenhouse for winter include:
Built-in Benches and Shelves
It would be a great feature if you can buy or build a greenhouse for winter that comes fitted with built-in racks or benches. These are important greenhouse equipment to have, as they serve as storage spaces and are very convenient. You’ll get more planting capacity while taking up less space. During winter, you don’t want to plant crops on the ground and shelves can keep everything from freezing.
There are specific greenhouse designs that don’t require heat or rely on it. However, not every greenhouse is made this way. Season extension heaters can provide some of the essential warmth, particularly in the evening hours, to prevent chilling and delay winter’s impact. Electric heaters are very popular options, but you can also go with propane or gas heaters. They allow you to control the temperature inside your greenhouse day and night.
Always remember that when you plant seeds, they depend more on the ground temperature over the air temperature. If you can efficiently warm the soil for the seeds to sprout, they can usually tolerate cooler air temperatures. You’ll need to buy a reliable thermometer and understand the heat requirements of your plants for this to be successful. A good heating system is essential for a greenhouse for winter. While they need enough heat to survive the cold months, certain diseases will spread along your plants if you don’t check them.
With a greenhouse for winter, you concentrate more one the soil warmth than on the air warmth, so it’s popular to use heated water pipes below the soil.
Plants require some light to survive and photosynthesize. The light demands have to have equal wavelengths to the sun. This is why a conventional bulb won’t work, and the following are common choices:
- Compact Fluorescents – These lights are smaller and more productive than traditional fluorescent lights, and this is why you can use them on plants.
- Fluorescent Lights – These lights work well for raising herbs and other plants that don’t require a high amount of light. However, they don’t work well for flowering plants as they don’t put out enough light.
- High-Intensity Discharge (HID Bulbs) – These are the best choice possible, and they are the most expensive to buy.
- Incandescent Lamps – These lights work well as grow lights for houseplants, but won’t work for an indoor setup.
Steps to Set up a Greenhouse for Winter
Because the greenhouse has to be heated through the cold months, it opens the door for a huge range of uses. Obviously, the main use of a greenhouse for winter is to give you an artificial growing climate for gardening purposes, and it can also support different plant varieties that you may not be able to grow where you live. They also help you plant year-round, extend growing seasons, create indoor gardens wiht landscapes, and allow you to make harvestable gardens in your backyard in winter.
Step One – Winterize
Spring is when you do spring cleaning, but for anyone who owns a greenhouse, early winter is the perfect time to clean it up a bit in anticipation for the changing seasons. The winterizing process is very routine for greenhouse owners, no matter if you plan on keeping it as a greenhouse for winter or not. It’s essentially your chance to clean up for later summer and the fall harvest seasons. The goal is to get the greenhouse in excellent shape before the snow flies. This means very thoroughly cleaning out any organic materials in the greenhouse before you scrub and disinfect the walls and equipment you have in the space.
It’s also a great chance for you to inspect every moving part in your greenhouse for any maintenance needs, which you should replace or repair long before the snow flies, which will help you get a happy and healthy greenhouse when the temperature starts to drop for the season.
Step Two – Decide on Plants
Have you ever tried to grow a mango in arctic conditions? This isn’t obvoisly going to work as the plant needs much more heat and light than you’ll ever get in an arctic environment. Growing into the winter months, even growing crops you do very well with in summer, can have issues.
This is why it’s critical when you plan your greenhouse for winter to pick crops that you know will do well in the more extreme conditions. While the greenhouse can mitigate many of the biggest damaging aspects of the winter, growing in snowy and northern climates will need to plant hardy root vegetables and leafy greens to ensure they have success when it comes time to harvest it.
Also, having a producing greenhouse for winter is possible due to the existence of cool-season plants that can survive near-freezing temperatures. You can start with the following vegetables and grow them throughout the winter season.
Planting broad beans during the winter months means that you’ll have young plants by the time early spring rolls around. The best method is to plant them inside your greenhouse for winter in beds. If the weather is still mild, putting the beds by the door means that you can easily have bees pollinate them.
Garlic comes in several different varieties, and planting them in your greenhouse for winter is very simple. They have a long growing season, just like onions.
- Chesnok Red – This is the variety to pick out if you’re searching for a more full, potent garlic flavor.
- Wight Cristo – If you want traditional garlic that you find used in cooking recipes, this is the variety to go for.
Garlic is a very popular plant to have in greenhouses since it’s easier to grow and keep healthy.
Herbs can enhance every meal you make, and there are herbs that are much more sensitive to cooler temperatures. However, there are herbs that thrive in colder climates, and they include:
- Chives – Chives are so easy to grow that they’re perfect for beginners or your kids. You put the seeds in a pot and put it in a dark place.
- Mint – Mint is a very flexible herb that will grow throughout the winter months. It’s like a weed when you grow it without a containment system, and it’s challenging to get rid of.
- Parsley – This is one of the hardiest herbs to grow, and it slows down the growth during winter. However, it can survive without protection too.
- Rosemary – Rosemary is a perennial herb that you can plant at any time during the year as it’s strong enough to protect itself from the cold weather. It can thrive all year round.
Winter temperatures sweeten leafy veggies. A few examples of cold-hardy, healthy leafy winter vegetables include lettuce as it flavors in cold weather. It’s a great spring or fall vegetable that can survive in the coldest climates. Kale comes with Serbian cultivars that are very hardy, and they are soft and have a less intense flavor profile. It offers leaves all winter too.
There are several onion cultivars that thrive in a greenhouse for winter, and they can survive planting in an unheated greenhouse. A few popular options include:
- Electric – This is a very popular red variety.
- Radar – This is a yellow-colored cultivar.
- Shakespeare – This is a variety of white onion that does well in colder temperatures.
If you live in a climate that has milder winter weather, you should plant your peas directly into the ground close together to get a great harvest. One of the best pea types to plant in a greenhouse for winter is Meteor as it’s very cold-hardy.
Root crops are also a great addition to your greenhouse for winter. You can put most of these root crops right into the soil and dig them up when you need them. Some great root crops to consider include leeks, rutabagas, turnips, radishes, parsnips, beets, and carrots.
Step Three – Set up Lighting
Most of your vegetables won’t grow well in darkness, especially if you want big yields. There are so many crops out there that struggle to grow and produce when the sunlight starts to go away, and the long sunshine-filled days give way to later mornings that are colder and darker, longer nights. Setting up the correct lighting will ensure that your plants get everything they need, even in the dreary winter weather.
Step Four – Control Humidity and Heat
The colder it is outside of the greenhouse, the higher your heat demand will be inside to keep your plants warm. Whether you’re in a location with mild winters in the southern portion of the United States or if you have freezing storms up north, the sun’s heat might not be enough to keep the crops coming until spring. This is why you need correctly sized and efficient healing systems to keep your greenhouse for winter thriving and the crops producing.
But, it’s not only plants that need heat to keep them healthy throughout the winter months. Certain diseases love warmer temperatures as it gets colder outside, and the humid, warm greenhouse is the perfect place to take root. This is why you need to balance your humidity levels and heat, either by using dehumidifying systems or proper ventilation to prevent diseases from popping up in your crops.
Step Five – Harvest
One of the most common mistakes people make when they set up their first greenhouse for winter is to treat your harvests like spring or summer ones. While growing periods during other times of the year can easily result in a large harvest all at once, winter harvests should be spread out over the entire season. This means that you have to plan your scheduling, harvest whenever you need to, and allow the plants to regrow.
Many winter growers plant out the beds in rows that they can harvest one at a time, and this allows the rows that you harvest first to regrow and have a second harvest while you harvest the other rows. This way, you’ll get a cycle of fresh vegetables to last until the springtime. This way, you can get fresh crops at farmer’s markets throughout the winter as you need them.
With a winter greenhouse, you focus on staggering your harvests to give you a steady supply of vegetables instead of harvesting them all at once.
How to Care for a Greenhouse for Winter
When you set up a greenhouse for winter, there are five main tasks that you’ll have to do, including:
When you create garden beds, soil health should be at the top of your mind. You may find yourself working with aged manures, compost, chopped leaves, or other amendments between crops. It’s also a good idea to apply fertilizers, and they can be liquid or granular fertilizers to promote a great harvest and healthy growth. At planting time, it’s a good idea to add slow-release granular fertilizers and liquid fertilizers, like kelp or fish emulsions, monthly. Always follow your application instructions for whatever types of fertilizer you choose to use.
It’s very pleasant to harvest from your greenhouse for winter. You can pick your veggies from the mini loop tunnels or cold frames on your raised garden beds. You should be warm when you harvest your plants as it will be significantly warmer once you get inside the greenhouse than outside in the frigid winter temperatures.
Maybe you live in an area where getting deep snow isn’t uncommon. If you, you need to keep an eye on the snow load on top of your greenhouse for winter. You can get greenhouses that are specifically designed to withstand a heavy snow load, but it’s a better idea to get a soft-bristled brush and carefully brush the snow away from the top and sides of the structure. This will reduce the stress and weight on the greenhouse, and it’ll allow more sunlight to come in.
Ensuring that you have proper ventilation in your greenhouse for winter is one of the most important tasks, especially when it gets hot out. Some come with roll-up windows, sides, and a door to vent. In late autumn, you can roll the sides up a few inches to get good airflow, especially if the temperature go up to 40-degrees F. The inside of your greenhouse heats up quickly, and you want your winter crops to grow on the cool side to make them more hardy. If you keep the temperatures too warm in the end of the autumn months, your soft tender growth can get damaged when the temperatures start to drop.
Venting is also one way to reduce the condensation levels in the greenhouse, and condensation can encourage fungal disease to grow. Venting on more mild days can reduce how much humidity gets trapped in the greenhouse.
One big question people have is how often are you supposed to water from December through February or March? The amount you water will depend on the years as you will get an early freeze some years and you back off on your watering in November. Other years see the weather being on the mild side into late december, so you’ll water more.
You can use a hose to water, but you can also use a watering can that you fill up from the rain barrel by your greenhouse. During the spring and summer, you’ll water your greenhouse almost every day. During mid-autumn, you can cut back your watering schedule to once or twice a week as the temperatures start to drop and the days get shorter. In winter, you may not water unless the temperatures get above 32-degrees F.
You can easily water your greenhouse plants using a watering can or garden hose, depending on which is easier for you.
Innovative Ways to Heat a Greenhouse for Winter
Whatever type of greenhouse for winter you settle on, no matter if it’s plastic or glass, you might need to think about heating it if you live in a colder area. Where the temperatures drop below freezing, you may need to rig up a heating system to enable you to grow food all year round.
1. Ground To Air Heating
This setup works by putting plumbing into the ground below the greenhouse and having the pipes carrying air to heat the space. A ground to air heat exchanger system allows you to make the most of the sun’s heat that collects during the day inside the greenhouse. Fans will then pump humid, warm air from the greenhouse through a pipe network in the soil. Here, the soil will “collect” energy that gets pumped back into the space to stay warm at night. By using a thermostat and the right fans, you can regulate the temperatures inside of the greenhouse and keep them in the right range.
Another option that is slightly more expensive is to install a ground-source heating pump for the greenhouse. This involves taking heat energy that is below the ground and drawing it up into your growing areas.
2. Hot Water Heating
One way to give your greenhouse for winter gentle heat from below is to plumb all of your greenhouse beds with a pipework heating system for hot water. These systems were very common in 19th century greenhouses. However, in those days, the water usually was heated by coal boilers. Today, there are many more eco-friendly heating options to choose from to keep your greenhouse for winter comfortable.
The first thing you can do is purchase or make solar heating panels. These panels won’t work for electricity generation, but they allow the water to get heated using the sun. You may hear it referred to as hydronic heating. If you want to heat your water in a more low-tech and simpler way, you could consider putting coiling pipes inside of a composting system. In any compost heap, the decomposing materials will generate heat. The water passes through the pipes inside the compost heap before the pipes run into a polytunnel and they will transfer heat and keep the soil temperatures higher than they’d normally be.
Sometimes, you can get away with just solar water heating. In other cases, you may use the solar water heater to preheat the water to bring the water temperature up before it goes to the boiler.
3. Renewable Electricity Heating
A more conventional way to heat your greenhouse for winter in an eco-friendly way is to use renewable energy options. Unusually, this means you harness solar energy by using solar panels. You can use these panels to provide the small amounts of electricity needed to run pumps or fans or greenhouse heaters.
Generally speaking, it’s a better idea to try and heat the soil below the plants instead of heating the whole greenhouse. So, consider adding a piped underground heating system before you look into space heating options. You can also use renewable electricity via a water, wind, or solar setup to run an electric boiler for heat.
4. Wood-Fired or Biomass Heating
Finally, you can warm piped hot water for your greenhouse using the sun or decomposing materials. However, these may not bring your water to the required temperatures, so you may have to use a boiler. As we’ve already talked about, you can rub a boiler on renewable electricity. It’s also possible to use wood or other biomass forms to run the boiler to heat the greenhouse for winter.
You can create a rustic DIY system using a 55-gallon drum to create a wood-fired boiler. If possible, you can integrate your greenhouse heating system with a solid fuel stove in your home too. Using solid fuel is another great way to generate heat for your greenhouse to make a rocket mass stove. A rocket mass stove combines heat-retention with efficient combustion. Planters can go above heated shelving units that extend from the stove, and this is ideal for cold-winter spaces.
A greenhouse for winter is one way to extend the growing season and get more harvests each year, and they’re not extremely hard to set up. We’ve outlined the basic things you need and how to keep it healthy and thriving, and you can take this guide and create your own greenhouse for winter to increase your vegetable production this year.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.