The cold, winter garden weather stops many gardeners from doing what they love, but building a hotbed is a great solution to combating the cold winter weather. From hotbeds to cold frames, and polytunnel greenhouses; this guide is your winter gardening solution. We’ll cover:
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What is a hotbed?
A hotbed definition: A patch of decaying organic matter that generates heat while decomposing. Hotbeds let you sow, and successfully grow, vegetable seeds and tender plants outside in winter, by harnessing the natural heat generated from manure and straw – without electricity. The Victorians had two styles of hotbed—a mound or a pit—topped with a cold frame. This allowed it to be opened on warm days.
How to build a hotbed
You will need:
- Several large bags of manure
- A shovel
- A watering can with a sprinkler
- Last years compost
- A temperature gauge
- Plastic sheeting
“Did you know, horse manure combined with straw generates more heat the ordinary manure? It also stays warmer for longer.”
My hotbed
- Acquire fresh, hot horse manure – ideally up to one week old. Choose your hotbed location – if any grass is growing there, prepare the surface with two layers of cardboard to stop it from growing through. Next, shovel the manure on top. Remember, the deeper the manure, the hotter your bed will become and stay, for longer. Next, wearing wellies, carefully trample the manure to remove air pockets. Then, take your watering can (some people use urine, I use water from a water butt) and water thoroughly. Finally, cover with a layer of plastic and leave for one week.
- After one week, uncover the manure and use a gardening temperature gauge to learn the ground temperature. Then, add your growing medium on top – I often use last years compost or old grow bags. Again, cover with plastic and leave for one week.
- One week later, use your temperature gauge again to see how warm the bed is. Then, you can either sow seeds directly into the hotbed, move potted plants from your greenhouse, or plant small winter garden vegetables into the hotbed. Some people even sow seeds in trays and place them on top of the hotbed to speed up the germination process. Cover with the sheet plastic to contain the heat. Download our free garden planner to monitor your seeds and note when your crops will be ready for harvesting.
- As your plants grow and you wish to introduce light, you can either add a cold frame on top or introduce a lighting system inside. Remember, if you fully remove the plastic sheeting, the ground will lose heat much quicker.
- Once you’ve finished with your hotbed, you can either keep the rotted manure in the ground and grow more plants, or dig it out and scatter it around your spring vegetable garden as fertiliser.
What can you grow in a hotbed?
You can grow plenty of things in a garden hotbed system – but if you only plan to grow a few salad leaves, it may be worth doing so on your kitchen windowsill. Otherwise, try planting herbs, peas, beans, turnip, cauliflower, peppers, chillies, radish or potatoes.
The benefits of a hotbed
The advantages of a hotbed
- You can start plants much earlier
- It offers free heat
- You don’t need to have a large garden. Consider alternatives like large plant pots, an empty tonne bag or pallets lashed together (and lined inside to prevent manure from falling out)
- Afterwards, you can use the cooled, well-rotted manure around your garden as fertilliser
The disadvantages of a hotbed
- It can be a lot of hassle for a few salad leaves. If you’re going to make a hotbed, make sure the work is worth the effort
- Having access to enough horse manure
- Excess moisture can cause mould or fungal growth
To learn more about hotbeds, check out Jack First’s winter garden book ‘Hot Beds’.
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What is a cold frame?
A cold frame definition: A low enclosure (often made from wood) with a transparent roof that is used for growing and protecting plants from the cold and wind. Cold frames are designed to prolong the growing season in autumn and power-up the growing season in early spring. To maximise the natural light and heat available, position your cold frame southwards.
How to build a cold frame
Every gardener should enjoy the luxury of a cold frame. And the type of frame you choose will be shaped by your time, space, creativity and budget.
Cold frame kits
You can purchase a simple cold frame kit from Thompson & Morgan, from as little as £39.99 to help with your cold frame gardening. Choose from large, small, hinged or folding cold frames. If you really wish, you even buy a solar-heated cold frame.
How to build a cold frame from plastic bottles
If you have plenty of time, why not try building a cold frame from recycled plastic bottles? There are plenty of DIY cold frame ideas available, and if you have space, why not consider a larger, cold frame greenhouse.
Cold frame for raised beds
If you have a raised bed in your garden, you may wish to tailor a raised wooden cold frame. Choose your transparent material – like plastic sheeting, acrylic plastic or recycle old windows; then construct a sturdy frame for it to sit on. You could even build a cold frame from pallets – just remember to fill the gaps to prevent warm air from escaping.
How to build a cold frame with an old window
Some of the most common and cheap DIY cold frames are made from old windows. For ease, these can either be placed directly over a pit in the ground, or you can construct a wooden frame for it to sit on.
Cold frame for individual plants
While you can build a mini cold frame for individual plants, you can also use a cloche. This will warm up a small patch of soil for a single plant and protect it from frost. You can also make a DIY cold frame cloche by cutting an unwanted plastic bottle in half and placing the top over your plant.
Cold frame for small gardens
If you have a small garden and wish to use a cold frame, consider growing crops in a vertical cold frame, or wrap cling film around a plant pot to create a warmed greenhouse effect. Remember to check your pots for slugs and snails before wrapping, as the heat may wake slugs and snails from hibernation, and will eat your new seedlings. Our slug and snail repellent plant pots can help.
What crops can you grow in a cold frame?
There are no limits to what you can grow in a cold frame – but you may be limited by the seasonality of vegetables. If you wish to grow crops that will exceed the height of your cold frame, you may need to prop your cold frame open or choose a cold frame with a hinge. Some of the most common cold-frame crops are lettuce and spinach, but you can also grow:
- Carrots
- Radishes
- Chard
- Cucumbers
- Leeks
- Courgettes
- Onions
- Garlic
- Kale
- Cabbages
- Broccoli
- Cauliflower
- Beetroot
- Beans
- Melon
- Sweetcorn
- Aubergine
- Peppers
- Winter squash
- Pumpkin
- Tomatoes
- Potatoes
- Celery
The benefits of a cold frame
The advantages of a cold frame
- Can be placed over a hotbed
- Start the growing season sooner
- Prolong the growing season
- Save money by starting seeds earlier, eliminating the need to buy plug plants from a garden centre or nursery
- You can boost the internal heat by adding an second layer of plastic under the transparent frame
The disadvantages of a cold frame
- If your cold frame is low or unhinged, the plants you grow will not be able to exceed its height
- You have very little control over the temperature
Cold frame vs greenhouse (glasshouse)
A cold frame
- A small, enclosed structure
- Designed to start seedlings or grow low-growing plants
- Ideal for small spaces or gardens
- Can only be used for a few seeds at once
- Cannot control the air and temperature
- Does not include ventilation vents
- Can be bought or constructed with a hinged window for warm days
- Does not incorporate an irrigation system
- Costs £20+ for materials
A greenhouse
- A large, often glass structure
- Can be used to grow all sized of plants
- Better suited to larger gardens
- Can be used for lots of seeds or plants at once
- Can control the air and temperature
- Includes vents
- Includes opening windows and doors for warm days
- May incorporate an irrigation system
- Costs £300+ for a wooden or metal structure with glass
What is a polytunnel?
A polytunnel definition: A long, semi-circular structure built from steel and covered in polythene. They’re often used for growing plants and vegetables that require warmth, directly in the ground. They work in the same way as a greenhouse – by heating up the soil with the sun’s rays. Some industrial polytunnels can be up to 16ft wide, and are referred to as a polytunnel greenhouse or a hoop house. During winter, some people use a polytunnel heater to keep the air warm enough for plant life.
How to build a polytunnel from scratch
If you have the time, it can be very satisfying and cost-effective to build a homemade polytunnel. They have two main elements – the polythene cover and the metal hoops. To build a polytunnel, you will need:
- 6ft lengths (48mm exterior) scaffolding poles – how many, depends on how long you want your polytunnel to be
- Blue mains water pipes (55mm interior) to cut to length – you will need half as many pipes as you do scaffold poles
- 1 x spirit level
- 1 x lump hammer
- 1 x block of wood
- 1 x tape measure
- Sturdy nails
- Submerge one scaffolding pole vertically, 3 foot into the ground, and use your spirit level to ensure it’s straight. You may need to place the block of wood on top and hammer it in. Then, position a second scaffolding pole 5 feet away, 3 feet deep. This will form the width of your polytunnel.
- Place one end of the blue water pipe on top of one of the scaffold, then bend it upwards, so the apex is 8 foot high between the two pieces of scaffold. Position the other end of the pipe over the scaffold, then secure both ends by drilling a hole, securing with a nail and bending the end.
- Position two more scaffold poles 5 foot away from these, then secure another water pipe. Continue doing so, until your polytunnel is the desired length.
- Then, you will need to purchase a polythene cover.
Mini polytunnel for raised beds
There are lots of different types of polytunnels for raised beds; from small, connecting polytunnels to ones that can trade polythene for netting covers in summer. The possibilities are endless.
How to hotbed a polytunnel
To hotbed a polytunnel, follow the instructions at the top of this page. However, there is no need to cover your bed with a layer of plastic sheeting. Decide between building a raised or a pit hotbed, then, consider whether to install an irrigation system. You may find ‘The Polytunnel Book’ by Joyce Russell helpful.
The benefits of a polytunnel
The advantages of a polytunnel
- Polytunnels can be cheap to buy, move and maintain
- They prolong the growing season, allowing you to grow more crops throughout the year
- You can grow more Mediterranean crops
- They can become warmer than a greenhouse when covered with a thermal polythene
- They come in lots of different sizes, so its easy to find the best polytunnel for your garden
The disadvantages of a polytunnel
- It must be positioned in a sheltered spot away from the wind
- Too much snow can damage the structure
Foods, plants and crops that grow in winter
What vegetables grow in winter
Make the most of your winter vegetable garden. These are the best vegetables to grow in winter – in the event of a cold night, keep a roll of horticultural fleece on hand. If you wish to produce any other vegetables, search by ‘the best vegetable strains to grow in winter’.
- Turnip
- Broccoli
- Parsnips
- Chard
- Cabbage
- Kale
- Leeks
- Chicory
- Beetroot
- Brussels sprouts
Herbs to grow in winter
While their growth may be minimal, these herbs can survive cold, winter weather. For an on-going, continuous supply of herbs, bring yours inside and store on a kitchen windowsill. For chives, grow them indoors on a south-facing windowsill.
- Basil
- Rosemary
- Thyme
- Mint
- Parsley
What flowers grow in the winter
If it’s colour you’re after, there are plenty of flowers that grow in winter to brighten up the long days. You may also wish to grow bulbs indoors during winter, like hyacinths or amaryllis.
- Pansies
- Cyclamen
- Heather
- Helleborus
- Dogwood
- Iris
- Witchhazel
- Snowdrops
- Christmas box
- Crocus
- Daffodils
- Winter jasmine
- Daphne
What trees grow in winter
Lots of people ask if trees grow in winter, and if you pick one from the list below, you can enjoy beautiful colours all winter long.
- Witch hazel
- Evergreen
- Conifers
- Holly
- Viburnum
- Mahonia
- Winter cherry
- Magnolia
Frequently asked questions
Does grass stop growing in winter?
Different types of grass either grow slow or stop during winter – this occurs when the soil and air temperatures dip below 5°C. For a grass that grows in winter (albeit minimally), choose a perennial. For a grass that stops growing, choose an annual.
Why do people wee on plants?
Due to the average human diet, most fresh urine is high in nitrogen, low in potassium and moderate in phosphorous. This makes it an excellent liquid fertiliser or compost accelerator.
How to prepare vegetable garden for winter?
Spread a thick layer of mulch over your beds to protect the soil or remaining plants from the cold weather. Or, for more winter garden jobs check our garden guide to caring for your winter allotment.
How to prepare vegetable garden soil for spring?
Amend your soil with plenty of mulch and prepare to warm your soil with plastic sheeting, horticultural fleece or bubble wrap. For more spring vegetable garden jobs, check out our garden guide.
Can pumpkins grow in winter?
Pumpkins are best started in April after the last risk of frost, grown through summer and enjoyed during winter. If a pumpkin is exposed to freezing temperatures, it will turn mushy and cannot be eaten.
Can I grow vegetables inside during winter?
Yes, you can. Use a good quality potting mix and sufficiently deep pots. Remember to keep them on a warm, light windowsill and consider plant lighting if your windows don’t receive sufficient light.
So, we’ve unearthed…
Three different ways to continue gardening through winter, and the differences between a hotbed, a cold frame and a polytunnel. We’ve also learned, that during the cold, winter months, it is even possible to grow crops on your kitchen windowsill – but they may require specialist growing lights for the best results. Each method has its advantages and drawbacks, but can, with time, really help you to get ahead of the season.
Do you have a favourite winter growing method? And what would you like to try and grow next winter?
Rebecca is the face behind Urban Undergrowth. She became addicted to gardening before it became popular and started writing this blog as a way to share her learnings. After all, sharing is caring. When she’s not digging potatoes, carrying caterpillars or sprinkling cinnamon, she’s a copywriter, painter, vegan chef and Muay Thai fighter.
Follow her journeys across the internet:
A quick guide to building the best soil for plants in your garden
The winter garden: Your guide to hotbed, cold frame and polytunnel gardening
*Please note, all information was correct at the time of publishing.