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Grow fresh food 365 days a year — we show you how with a winter greenhouse!
As the colder months approach, a lot of plants stop growing in the garden. But the great news is that you can extend the growing season by gardening in a greenhouse over winter.
If you want to grow your own food all year round, a greenhouse is a good investment. It doesn’t need to be expensive or permanent. There are greenhouses of all shapes and sizes, so even if you only have a small space, you can find something that works for you.
In this complete guide to winter greenhouse gardening, we’ve covered everything you need to get started.
Why use a greenhouse in winter?
There are lots of benefits to winter greenhouse gardening, as you’ll see below.
The great thing is that many plants will grow in greenhouses over winter without the need for additional heating or light. This cuts out the worry of an expensive power bill.
Let’s check out some of the reasons why winter greenhouse gardening is such a good idea.
Grow Food All Year Round
First of all, you can extend your growing season if you like to grow your own fruit and vegetables. It’s possible to grow salads, fruits, vegetables and herbs in the winter with careful planning.
Garden Away from the Elements
Growing in a greenhouse over winter means you can garden away from the weather. If you live in a cold place with winds and snow in the winter, you may find this a welcome benefit.
Protect and Grow Tender Plants
Moving tender succulents and exotic plants into the greenhouse over winter will protect them from freezing temperatures. Having a greenhouse gives you the scope to grow tropical plants.
What can you grow in a winter greenhouse?
It depends on your local climate, how much space you have and where your greenhouse is situated in the garden.
If you have freezing cold winters, you’ll need to stick to growing plants that can take low temperatures (unless you are heating a greenhouse). In milder climates, you should be able to grow throughout the winter without the need to protect greenhouse plants.
Types of Winter Vegetables
Lots of hardy vegetables will grow well in cold conditions. Some actually need low temperatures to thrive.
For winter veg try: kale, carrots, onions, garlic, cabbages, parsnips, scallions, beets, endive, arugula, leeks, winter lettuces, chard, bok choi and spinach.
Top tip: Check which vegetables are winter-hardy varieties when you’re choosing your seeds. Some seeds will have ‘winter’ in the name which gives you a clue.
Types of Hardy Herbs
Parsley, coriander, dill, rosemary, sage and thyme will all continue to grow in colder temperatures. You should have fresh herbs throughout the winter if you keep them in the greenhouse.
Types of Fruits
There are quite a few grape varieties that will live happily in an unheated greenhouse, depending on where you live. Check what temperatures they will survive at before you buy. Black Hamburgh is an excellent choice that will survive cold winters.
Peaches and nectarines grow well in pots under glass. Growing citrus fruits like lemons, limes and tangerines is possible if the temperature in your greenhouse stays above 10 ֯C.
Get a Headstart for Spring
As well as growing throughout the autumn and winter you can start your spring and summer crops in the greenhouse, ready for planting out when the weather warms up.
Cucumbers can be sown in the greenhouse from late winter onwards. You can sow aubergines in January-February. Start tomatoes and peppers in early spring.
When to Start Growing Winter Crops in your Greenhouse
The timing is everything. Get your winter greenhouse gardening plan drawn up in the summer, so your crops will have enough time to grow. You’ll be harvesting throughout the winter, so look at the length of time plants take to mature.
Many leafy greens are fast-growing at 1-2 months. Some crops (carrots, onions, beets) can take over 3 months to mature. So, if you want to get a December harvest, you’ll need to start sowing some root vegetable seeds in late September and early October.
If you have cold winters that set in earlier than December, think about starting your winter veg as early as August, so that the crop matures just as temperatures begin to drop.
Top tip: Choose plants that have similar needs (light, humidity, watering), so they will all be happy growing together in one greenhouse.
Winter Gardening: Types of Greenhouse
Different Greenhouse Sizes
You can get all shapes and sizes of the greenhouse. There are metal-framed, PVC-framed and wooden-framed structures. Your choice will depend on the sort of look you like, the space you have and your budget.
Which greenhouse shape is best?
Most people picture the classic rectangular greenhouse built of metal or wood with glass panes. You can get many greenhouse kits now with polycarbonate windows rather than glass.
Lean-to greenhouses are great space-savers and will be suitable for most yards because they can be set up easily against the wall of your house.
The rounded dome shape of a geodesic greenhouse is brilliant for cold weather conditions because it shrugs off snow and wind very well. You can buy them with polythene, polycarbonate or glass panels.
A polytunnel with hoops and plastic sheeting is cheap to set up, but you might need more room for this shape than some other greenhouse types.
You can also buy mini-greenhouses for tiny spaces like the one pictured above. This straightforward style is easily replicated with wood and polythene sheeting if you have some DIY skills.
If you have space, we think a geodesic greenhouse is perfect for winter growing. It will withstand winds and snow and doesn’t need to take up a lot of space. A 15ft dome should feed 2-3 people throughout the year.
What about heating a greenhouse?
Look for greenhouse kits with solar-powered heating and cooling systems. This makes them a sustainable and energy-efficient investment.
You should also look at insulation before you think about heating. Even in freezing outdoor temperatures (-20 ֯C), plants can survive in a greenhouse. Many cold-hardy vegetables actually need colder conditions to thrive. It can be -5 ֯C outdoors but about 10֯ C inside your greenhouse just from the power of the sun.
Insulation of individual tender plants is quick to do with a bit of bubble wrap or fleece around the pot to protect roots.
Easy Ways to Insulate a Greenhouse without Electricity
- Straw bales arranged around the inside of your greenhouse will reduce heat loss
- Bubble wrap around pots and lining greenhouse walls makes an excellent insulator
- Plastic bottles and barrels painted black and filled with water. This passive solar set up will absorb the sun during the day and release it into the greenhouse at night
Choose the Best Site for your Greenhouse
Think about where you will put the greenhouse. If you have limited space, a lean-to or mini-greenhouse is a good option. Choose the sunniest spot you can. Avoid overhanging trees and shade-casting buildings. Rule out any areas that are too steep or sloping as this will make putting up a greenhouse more difficult.
How to Grow in a Winter Greenhouse
Why Raised Beds are Great
You can grow straight in the ground inside your greenhouse. But setting up raised beds has lots of advantages as well as making it easier to harvest crops, raised beds to help to keep soil temperatures regulated.
They need less watering. Plus, you can avoid transplanting crops from one place to another, which can stress plants. You will also be keeping plants out of and away from the freezing ground in winter.
Planting Seeds in Pots
Choose the right size pots for your plants. If you are growing root vegetables, you’ll need plenty of depth. It’s a good idea to plant seeds where you expect the full-grown plant to stay so that you don’t need to move them into bigger pots. Transplanting adds unnecessary stress to the plants in winter and involves more work too. Keeping containers on shelving or tables gives easy access.
Add Good Quality Soil
Having enough depth for root vegetables is vital. Use good quality soil and compost. It’s a good idea to enrich the growing medium with organic fertilizer before you plant anything.
Winter Greenhouse Gardening: Plant Care
Once you have your greenhouse set up and ready to go, you’ll want to make sure your crops make it through the winter. Caring for your winter greenhouse crops involves just a few simple tasks.
As we said above, enrich the soil with organic fertilizer before you sow your crops and you probably won’t need to feed the plants much at all. Liquid fertilizers (for example seaweed-based feeds) can be added later if needed.
You might water daily in your greenhouse in the spring and summer months. In the autumn, this will reduce to perhaps once or twice a week. In the winter you need to water even less, especially if you live in an area that freezes up. It’s useful to have a water butt set up nearby, as plants prefer rainwater.
Air Circulation or Venting
If you have some warm days, get the air flowing through your greenhouse to reduce condensation, which can encourage fungal diseases. Open your greenhouse windows and door; roll up side flaps. Some greenhouses have automatic ventilation systems which do this job for you.
The weight of snow on a greenhouse can be a problem – remove carefully with a broom from the outside if you have glass or polycarbonate panels. If you have a polythene-covered greenhouse, you can do this from the inside by carefully nudging and sweeping the ceiling.
Plant Growth Slows Down in Winter
If your vegetables seem to be taking a long time to mature, just remember that they will grow more slowly in winter compared to summer. They probably won’t grow much at all in the coldest months. This is why it’s a good idea to get some veg to maturity as the colder weather starts to set in, so you can harvest through the coldest part of the year. And if they don’t reach their full potential, they can still be picked at a smaller size.