DIY cold frames to protect your plants: simple and quick to make

The purpose of DIY cold frames is to extend the summer growing season into the cooler months. You can buy ready made cold frames or kits which are self assembled, but it is easy to create a makeshift one out of common household objects like plastic bottles. Or even to create something more permanent from unwanted reclaimed materials such as bricks or doors.

These easy-to-erect DIY cold frames will mean you'll quickly be able to start your seedlings and plug plants and harden them off before they're planted out in your garden in spring. Not only will this improve performance, it speeds up their establishment in the garden too.

In the colder months of the year, you can use your DIY greenhouse designs and cold frames to overwinter seedlings and get a head start on next spring. You can even use them to sow trays of vegetable seeds like cabbages, lettuce, and peas for super early harvests the following year. 

Protect seedlings and plants with DIY cold frames

Just like our favorite greenhouse ideas, these DIY cold frames are a brilliant way of improving your vegetable growing as well as providing a perfect environment for hardening off plants. They're budget friendly and easy to make too. 

1. Create a frame with old bricks

'My cold frame was very easy to construct and cost me nothing to make,' says Aoife, who showcased her DIY cold frame on @green_aoife on Instagram. 'I used bricks that we'd taken out from an internal wall during a bit of house renovating and an old, broken, hinged shower door. I stacked the bricks against one of our garden walls to make a rough rectangular frame and then put the shower door on top as a roof. 

'The hinge action on the shower door allowed me to open and close the cold frame with very little effort. I used the cold frame to help harden off my seedlings ready for planting out in the mini veg garden. I had a really small garden space at the time and tried to pack a lot into that tiny area.

'The next year I dismantled the cold frame and used the bricks to create fruit bush planting spaces. I used the shower doors at my allotment as makeshift cloches!' 

Cold frames don't need any heat sources so are a really easy solution, whereas you may have to heat a greenhouse if you're wanting to grow certain crops.

2. Repurpose an unused wardrobe

Jess @theallotmentgeek first started her allotment journey, aiming to reuse as much as possible to keep her carbon footprint down. 'When we had a wardrobe going unused at home, we found the perfect opportunity to create a new cold frame for our young plants.

'We knew it would need as much light as possible to help the plants thrive, so we cut out 4 holes of each of the doors and sides, leaving the top and bottom panels for stability, and then screwed polycarbonate sheeting over the holes to protect plants from frost and too much rain. 

'Once we did this, we secured the wardrobe back together with corner plates (two on each corner). As the wardrobe no longer had its back panel this was needed to help keep the structure sturdy, especially when needing to be moved around.  

'When it was in place we then painted the wardrobe with a clear exterior wood paint to prevent any water getting into the wood and rotting it, and it was good to go! With £20 ($27) and some creative thinking, you can easily create DIY cold frames.'

3. Use plastic drinks bottles as a lid

If, like us, you find yourself worrying about the amount of plastic which goes to waste every day, any new tricks on how to put plastic to good use are a welcome discovery. 

So here's a cheap garden idea where plastic soda bottles have been used to create a clear screen to act as a lid for your cold frame. A simple timber construction, or even an existing wooden box can be used as the base. Then create a frame to fit the top of your base using strips of wood cut to size and nailed together.

Make a hole at the base of your plastic bottles and feed a narrow strip of wood (bamboo canes cut to size are ideal) from top to base forming a column. Line these up next to each other and fix into your frames before attaching to the base of your DIY cold frame. It's an easy, eco friendly option for a sustainable garden. 

4. Construct a simple kit frame

Niki Jabbour of Savvy Gardening created this cold frame from a kit made from cedar wood and polycarbonate. 'I got it from a local building supply company and I just had to assemble the pieces. 

'I’ve also made cold frames from straw bales and topped them with old windows or a sheet of polycarbonate. Or I’ve built cold frames from hemlock boards and made polycarbonate cold frame tops for them. 

'I use cold frames to extend the harvest in spring and fall as well as to harvest all winter long. I live in a hardiness zone 5B and we have long winters with a lot of snow. Cold frames allow me to enjoy a harvest of cold season crops throughout the greenhouse growing calendar like spinach, winter lettuces, Asian greens, scallions, kale, carrots, and other hardy vegetables throughout winter.' 

5. Make use of an old window

Louise (@louiseashton_in_france on Instagram) made her DIY cold frame out of an old window from her house which needed replacing. Windows make ideal materials for DIY cold frames as the transparent glass is ideal for letting vital light to your seedlings. 

And to add a fun finishing touch to an already lovely looking cold frame, Louise took things one step further with a splash of outdoor paint. 'I painted it with a pop of pink to match my tomato cages,' says Louise. 'The color is bright it always puts a smile on my face and will do even more so when filled with young seedlings.' 

If you're using a really old window make sure you get it tested for lead content first.

6. Turn a plastic storage box into a cheap cold frame

Can clear plastic storage boxes be counted as DIY cold frames if there's no actually 'doing' involved? Perhaps the simplest idea of them all, these storage boxes make instant cold frames for your seedlings.

Make sure you go for clear plastic as you will need plenty of light in order for your plants to thrive before you transplant seedlings. The added bonus of using these is that the lids are pestproof too, so you won't need to worry about how to get rid of slugs or other garden critters. 

7. Use a raised bed as a sturdy frame

An existing raised garden bed is the perfect starting point for DIY cold frames. Their sturdy sides can be used as a base on which to attach a lid. 

It's easy to make a simple frame for the lid too, and a sheet of inexpensive polycarbonate is the perfect option for the panel in the center. It's lightweight, making it easy to lift, and the clear material will allow plenty of light to reach your plants. 

The best mini greenhouses allow you to ventilate the growing space on warmer days, so it's a good idea to incorporate a simple mechanisim so you can prop open the lid when it's warm and sunny. If you're feeling clever you can even attach hinges for easy opening.

8. Cover plants with plastic sheeting

If you only have room for small vegetable gardening ideas and can't fit in extra growing space or cold frames, simple plastic sheeting could be the answer to your dilemma. 

A clear plastic sheet could give tender plants and seedlings in a raised bed a little added protection from the worst of the weather. 

Inserting lengths of timber into the soil around the perimeter of your bed will help to lift the plastic off your crops and give them the space they need to grow. As plastic sheets are light you'll need something to weigh it down and keep it in place, but a few bricks or small rocks dotted around the edge should suffice. 

How do you make a simple cold frame?

The purpose of a cold frame is to create a sheltered environment which will enable you to extend the harvest in spring and autumn, as well as to harvest all winter long. This is particularly useful if you live in an area which has long cold winters. 

In order to create a simple cold frame, dig a hole at least 30cm deep. Or if you aren't able to dig a hole in your garden create a brick base. For the roof use a clear material which can be easily lifted to take your cuttings and seedlings in and out with ease. This could be a sheet of polycarbonate or a reclaimed window or old shower screen. 

On a smaller scale, something as simple as a good sized plastic box can make a good DIY mini greenhouse, as long as it has a lid. Or you can even cut the tops off plastic bottles and place these on top of your pots of seedlings.

Where should I put my DIY cold frame?

It’s best to position your cold frame on a flat, solid base – on top of a couple of paving slabs or on an existing patio is ideal. Choose a sunny spot where there’s plenty of light, but make sure it’s protected from cold wind.