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How to Build a Cold Frame for Plants

Written by PJ
03/03/2022 11:02:05

How to Build a Cold Frame for Plants

Cold frames are an easy DIY project for any keen, green-fingered gardener. With limited materials and tools, you can create the perfect growing bed to use all year round. Before constructing your cold frame, it is worth thinking about two important things:
  • Location: First, you need to find a suitable location for your cold frame. In order for cold frames to work effectively, they need to be in view of sunlight as it is the sun’s rays that provide heat. It is also worth finding a space that is sheltered from the wind as this can damage your plants. Keep in mind the need for water drainage as cold frames are bottomless structures. 
  • Size: The second thing you need to consider before building your cold frame is its size. Now, depending on the location, you may already have a good idea of how big (or small) your cold frame can be. The size should largely be directed by how many plants you intend to keep in your cold frame at any one time. 
Here are the tools you’ll need to build a cold frame for plants:
  • Wood screws
  • Measuring tape
  • Drill/Screwdriver
  • Wood saw
  • Hinges
The materials for a cold frame are:
  • Wood panels (Plywood or scrap pallets will do)
  • Glass/Polycarbonate (or an old window)
Here’s how to build your own cold frame:
The frame:
  • Begin by building the frame. Remember that cold frames typically have a pitched or slanted roof to allow water to slide off.
  • Using your timber or scrap wood, create a rectangular, bottomless box, screwing the wood together at each corner.
  • Secure a short wooden pillar to the inside corner of the frame. Make sure the pillars at the back are slightly taller than those at the front.
  • Build up the sides of your cold frame by screwing wooden panels into the pillars.
The lid:
  • Once the frame is made, you can build the lid. You can use an old window and attach this to the frame using a hinge. Alternatively, you will need to create a lid with either glass or clear polycarbonate plastic.
  • To make your own lid, you need to begin by building a frame for the glass or plastic using four strips of wood.
  • Once your lid is made, you can add it to your frame using the hinges.

We recommend using polycarbonate plastic for your cold frame glazing instead of glass as it offers greater protection for your plants and crops.

Polycarbonate is 250 times stronger than glass and impact-resistant, ensuring that it can withstand even the most extreme of weather conditions. Polycarbonate glazing is also easy to cut to any size or shape.
If you are not a virtuoso with woodwork, you can find a wide range of readymade cold frames online, including both wooden and plastic models.


What to Grow in a Cold Frame in Summer?

Though cold frames are primarily used through the colder months to keep young plants happy and harden seedlings, these green growing machines also provide you with lots of cultivation opportunities throughout the summer months.
In the summer, you can use a cold frame to grow…

  • Quick-maturing crops: Any warm-weather crop that matures quickly can be grown in a cold frame throughout the summer and even during the late summer! Some super speedy crops you might consider growing in a cold frame include radishes, green beans, and salad leaves.
  • Herbs: In the summer months, cold frames act as the perfect location for a herb garden! Basil, chives and oregano are the top herbs to add to your summer garden. You can also start growing cuttings or perennials.
  • Harden tender plants: Much like in the winter, the summer is also the perfect time to harden tender and delicate plants before relocating them to the garden. Bulbs and other corms are ideal to begin in a small cold frame during the summer months.


Using a Cold Frame in Winter

Cold frames are perfect to use throughout winter and during wet weather. They are incredibly versatile growing implements that are a lot cheaper to install than greenhouses and practically maintenance-free!
You can use a cold frame in winter to…

  • Extend the growing season: Cold frames are great to keep late-cropping vegetables in. You can use a cold frame to push through to the end of the harvesting season while ensuring that your plants have enough heat to grow in. This is why cold frames are great for growing different types of lettuce in! 
  • Start sowing seeds early: Due to their ability to retain heat, cold frames can create a suitable growing environment for many plants even before the spring arrives. Quick-maturing vegetables you typically begin to grow indoors—such as tomatoes and chillies—can be grown in a small cold frame instead.
  • Harden seedlings: Cold frames are particularly useful for hardening delicate and young plants, allowing them to acclimatise to poor weather conditions. This means your cold frame can act as a go-between when moving plants from inside the house to the garden.
  • Overwinter plants: Many overwinter plants can actually spend their entire life inside a cold frame. Leafy greens like spinach and kale can be sown in late summer and left to grow throughout winter inside a cold frame.


How Much Warmer Are Cold Frames?

Cold frames are the perfect location for growing plants during the cold winter months. In fact, they are typically between 5 and 10 degrees warmer than the temperature outside.

This means they protect alpine plants during the winter and allow you to begin sowing seeds earlier in the year!
Keep in mind, however, that if cold frames get too hot they can roast your crops. To avoid your cold frame overheating, make sure to install a vent (with a closing mechanism) that you can open every 1-2 days to allow some hot air to escape from.

Small circulation fans can also be positioned inside a cold frame to help fresh air flow throughout the structure. 

Here at The Plastic People, we provide polycarbonate cold frame glazing cut to any size or shape! If you are looking for indestructible glazing for your cold frame, you can get an instant quote on our website today!

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