How to Grow in an Unheated Greenhouse

Growing produce all year round in a greenhouse is something many green thumbs dream of. When you take a dive into looking for a new garden shed or greenhouse, so many questions might pop into your head. The main one being how to grow plants and vegetables in an unheated greenhouse during those cold winter months.

Keep reading below to find out more about growing the perfect plants in an unheated greenhouse in winter!

The Essential Benefits of Greenhouse Gardening

There are so many incredible advantages of owning a greenhouse besides being eco friendly. They can be a great hobby for those who love immersing themselves in nature.

You don’t always need to control your greenhouse temperature. There are plenty of ways to have your plants thrive in an unheated greenhouse. The benefits of greenhouse gardening are extensive and far outway the cons.

BillyOh Polycarbonate Lean-To Greenhouse
BillyOh Polycarbonate Lean-To Greenhouse

1. Ultimate Weather Protection

A greenhouse can provide your garden produce with protection all year round, not just in the cold weather.

Your plants will not only be protected from the weather such as harsh UV rays or heavy snow. It’ll also keep them protected from those pesky animals trying to find their way in. Having a greenhouse in autumn or a greenhouse for winter can provide benefits just as a greenhouse would in summer!

BillyOh 4000 Lincoln Wooden Polycarbonate Greenhouse
The BillyOh 4000 Lincoln Wooden Polycarbonate Greenhouse

2. All-in-one Gardening Place

Having a greenhouse allows you to have a designated area to grow your much-loved plants and vegetables. This means your garden won’t be overflowing with your incredible looking plants. Instead, they will be tidy and nicely tucked away. A great option if you don’t want your plants ruined by visitors!

It’ll also be a great idea to keep all of your tools and equipment in the same place so you never have to misplace them again!

Dragonfly on plant leaves

3. Pest Prevention

Although you’re clearly a nature lover, there’s nothing more annoying than pests and animals coming to damage your much-loved plants. With a greenhouse, your plants will have a place to thrive and grow without the disturbance of any unwanted guests. Especially during those cold winter nights.

Your greenhouse’s enclosed structure means you never have to worry about visitors creeping onto your plants again!

4. The Freedom of Growing Whatever Plants You Want

Knowing and understanding your greenhouse environment is crucial to growing produce. Once you do, there’ll be an unlimited supply of the types of plants you’ll be able to grow!

You don’t have to stick to just one type of plant. You can expand your knowledge and love of nature by delving into brand new vegetation. Some of which are perfect for a greenhouse in winter.

Assortment of vegetables

An Unheated Greenhouse

Besides what you might think, an unheated greenhouse can come in handy during those cold winter months. Whilst a temperature-controlled greenhouse may seem like the better option, unheated greenhouses can actually be more beneficial. You can grow those hardy plants with ease and get some great looking healthy plants!

Some great examples of winter-hardy plants and green vegetables include:

  • Broccoli
  • Brussels sprouts
  • Cabbages
  • Kale
  • Leeks
  • Parsnips

There are so many more options of vegetables you can grow in a greenhouse of course. No matter the type of plant you want to grow, an unheated greenhouse should be perfect!

An unheated greenhouse is also known as a cold greenhouse. The cold greenhouse is generally constructed in a cold frame or hoop type of garden building. Whilst it can protect the plants inside your greenhouse from harsh weather conditions, it can also soak up the sunlight at the same time.

Although you can grow plenty of produce in a greenhouse where the temperature can be controlled, this may lack heat. This could result in limited options. These would be known as a heated greenhouse.

Your typical greenhouse will trap heat from the sun. Without added protection, it can also cause frost damage in your greenhouse at night during the colder months.

Cold frames can keep your plants and soil around 5 to 10 degrees higher than the outdoor temperature! This naturally will prolong and extend the growing season for your plants by multiple weeks.

A bundle of pumpkins

A Few Tips on How to Use Unheated Greenhouse

1. Starting Seeds

If you’re looking to grow seeds, the perfect time for this is in the cooler months. Seed germination tends to occur in colder climates so late winter and early spring are perfect times!

If you’re looking to grow straight from the ground, it’s best to prep the soil first by building your greenhouse in the best position. This would be in direct sunlight early in the morning and is best done around 2 weeks before planting.

If you’re aiming to grow warm-season plants, it’s best to start planting these into the ground around one to two weeks before the last frost dates. Warm-season plants include:

  • Pumpkin
  • Winter Squash
  • Sweet potato

2. Hardening Off

Acclimating plants is so important. For example, any houseplants you may have got from a garden centre would need to be carefully introduced into their new environment.

It’s important to acclimate plants to reduce the amount of difficulty your plants may have adapting to a new reduced temperature. When you acclimate your plants, you’ll also help thicken the waxy leaf covering they have!

When it comes to seeds and seed trays, cool-season plants such as broccoli can be acclimated a week earlier, whilst warm-season plants can begin the acclimation process two weeks before the last frost dates in your area.

However, if you’ve bought a plant straight from the store, you can place this straight into the cold frame for acclimation.

Various seeds in plastic pots

What You Can Grow

Now you’ve bought your greenhouse and you’ve got it placed perfectly, the exciting part can begin. You can start growing your vegetables!

If you’re stuck on what leafy greens can grow, here are some great examples perfect for your fresh salads. You don’t have to just stick to the common root vegetables!

Try planting:

  • Cabbages
  • Brocolli
  • Celery
  • Peas
  • Brussels sprouts
  • Carrots
  • Asparagus
  • Snow peas
  • Radishes

All of these much-loved vegetables above are perfect starting points for your brand new garden greenhouse!

What to Expect

No matter the weather, your plants can still survive, even in the closest months!

Bear in mind, during the winter months, plants won’t grow as quickly as they do during the summer months. Some plants may not reach their full potential but this won’t be a problem when it comes to harvesting them. They’ll be just as good!

During colder months late winter months like January and December, some plants may not grow for several weeks. This also isn’t a problem! As long as these plants don’t die, they’ll be perfect to harvest and thrive in this environment. Winter greenhouses can be ideal!

Ladybug on a leaf

Tips for Successful Winter Gardening 

Now you’ve got everything ready and you know what you’re wanting to grow. Here are a few last-minute tips for gardening in winter during the cooler environment!

  • Space – Make sure you have enough greenhouse space for your plants. Overcrowding them can limit their growth potential and could cause them to die. Make sure the leaves don’t touch and they’ll thrive!
  • Raised garden beds – If this is what you’re interested in, make sure you thin out the weak plants. This is to give the hardier plants room to grow.
  • Signs of disease – If you see any signs of disease on your winter vegetables, remove these plants straight away. This is to prevent this from damaging your other produce.
  • Pests – If you want to ensure pests are kept away, try planting marigolds. These have natural pest repellants in them!
  • Ladybugs – These beautiful insects are considered beneficial to your greenhouse. They can help to keep those pests under control!

Once you’ve taken all of these steps into consideration, you’re ready to create the perfect greenhouse! Grow those incredible colourful flowers or those tasty garden vegetables. If you’re still a little unsure about which greenhouse is best for you, take a look at our range of incredible greenhouses!

You can find polycarbonate greenhouses and glass greenhouses, so whichever you prefer, the right one is there for you. Now is the perfect time to take the leap and get planting!

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Yes! Your unheated greenhouse can hold onto warmer temperatures than the outside, meaning your plants can stay frost-free!

Yes! You’ll be able to wake up in the morning to plants that are alive and thriving.


Your unheated greenhouse will only be heated by the sun. This means that if the temperature is 0 degrees, for example, your greenhouse temperature will be 5 degrees celsius. It will always be 5 Celsius above the temperature outside.

Yes, you can. Take a look at our ‘What you can grow’ section above to see some of the perfect vegetables to grow in winter!

No. Your greenhouse will need a solid and level base to sit on. We recommend concrete, but decking or paving slabs would also be fine. Take a look at how to build a base!