​Cold frame gardening

​Cold frame gardening

Posted by Alix Francis on 6th Nov 2017

Your growing season doesn’t have to come to an end when the weather starts to get colder, there are many choices available on how to extend your growing season, one of them is by using a cold frame.

Cold frames are essentially small, simple greenhouses that protect and shelter your plants from the cold weather. They are built like a raised bed with a clear lid (Glass or Twin wall) attached to it. The clear lid lets in heat from the sun, warming your plants whilst keeping them protected from the elements creating a microclimate that is warmer than your garden.

You can extend your growing season by up to 60 days (depending on where you live) with a cold frame, it’s one of the easiest ways to grow vegetables regardless of the climate.

Where to position your cold frame

Once you’ve got your cold frame, you will need to site it somewhere that is sunny and sheltered, this is so plants and seedlings get as much light and warmth as possible.


Ventilation is a top priority when it comes to growing in a cold frame, the daytime temperature can fluctuate dramatically during autumn or spring which means you can easily cook the plants you were trying to protect from the cold! You can purchase an inexpensive automatic vent opener to ventilate your cold frame when it hits a certain temperature.

Several issues can crop up when you don’t ventilate your cold frame, one of the being frying your plants. You don’t want your Autumn or Winter crops growing in conditions which are too warm for them, it could encourage soft growth which is easily damaged in cold weather.

Investing in a thermometer to monitor the minimum and maximum temperatures of your cold frame will be incredibly beneficial.

Compost and manure

Start growing in your cold frame with a healthy dose of compost and manure. Add the compost and manure before you add your plants, it can be quite difficult to add compost and manure to a cold frame once there are already plants inside it. Remember not to over fill your cold frame with soil, plants will need good room to develop and grow.

Plant in rows

Plant your seedlings and crops in tight rows so you can benefit growing more crops in a tighter space. Keep on top of 

Seedlings ready for cold frame

weeding and be sure to remove anything that sprouts outside of the designated rows, this is to reduce the competition for nutrients and allow your plants to flourish. You can keep weeds to a minimum by adding newspaper, straw or mulch between the planted rows.

Watering plants

As the cold frame will be covered by a lid, it’s important that you water your plants regularly, it’s best to do this in the mornings so your plants have something to drink throughout the day.

Keeping the cold frame clear

Always be sure to keep the top of your cold frame clear, you don’t want to risk your plants and seedlings going without light for too long. Leaves can quickly build up during the Autumn months and leave your plants with a lack of light.

Boosting light and heat in your cold frame

There will be times when you feel your cold frame could do with a little boost of light and heat. There are a couple of ways you can do this easily in your cold frame. One way to give your cold frame a boost is by painting the inside walls of the structure white or another way is by lining the structure with aluminium foil.

Starting with cool-season crops

You might want to use your cold frame to start cool season crops, these include:

  • Beetroots
  • Broccoli
  • Brussels sprouts
  • Carrots
  • Kale
  • Cabbage
  • Lettuce
  • Peas
  • Radishes
  • Spinach
  • Turnips

Once they have been sown and planted in your cold frame, that’s where they will live until they are ready to harvest so choose your cool season crops wisely.

Transplanting cold-hardy seedlings

Sometimes you will want to start your crops off indoors then move them to a cold frame to be hardened off.

Hardening off is a one-week process where seedlings which are originally started indoors become acclimated to the outdoor elements such as temperature fluctuations, wind, sunlight and cold nights.

For hardening off your seedlings in a cold frame you will need your thermometer to monitor what temperature the cold frame is inside. Once you have moved your seedlings to the cold frame you will need to keep checking on them over the next couple of days, keeping them in their trays, pots etc. until they are ready to be planted in the cold frame, typically after a week.

Here is a list of cold-loving vegetables that can be planted as seedlings:

  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Collards
  • Kale
  • Lettuce
  • Onions

Transplanting heat-hardy seedlings

Thanks to your cold frame, heat-loving vegetables can be started indoors three weeks earlier!

You can start warming your garden bed up with your cold frame on the same day you start your seeds indoors.

Keep the lid closed and add a protective inner layer onto the bed, set your thermometer in a shady spot inside the cold frame and monitor the temperature. When you’ve got a good temperature around 20 degrees Celsius and you’re able to maintain that temperature, it’s time to start planting your seedlings. Use the same method used above for transplanting cold-hardy seedlings by keeping them in their trays, etc. for a week until they have acclimatised and are ready to be planted.

Once you know what you want to grow in your cold frame, it’s easy enough to get started. Maintaining and keeping your cold frame the right temperature is key to the success of your cold frame gardening.

Interested in cold frame gardening?

Browse our range here.