Planning to build your perfect garden cold frame? Well, please know that the plastic sheets you choose will make or break the success of your growing cold frame.
Arguably the clear plastic you choose for your cold frame has the biggest impact on how efficient your cold frame will be as a growing environment. How long they last, whether they are UV protected, what they are made from and many other factors affect which sheets will be right for you.
What is a cold frame and what do you use it for?
A cold frame is a low-lying box structure with a transparent roof to let light in, that is primarily used for protecting seedlings and other young plants from poor weather conditions. They are a fantastic addition to any garden and are very popular with gardeners of all types.
In essence, a cold frame is a mini greenhouse!
With cold frames for gardening, you can extend the growing season by protecting vegetables and plants from the frost and enjoy gardening all year round.
4 reasons to use a Cold Frame:
- Shield against frost and harsh winter conditions
- Allow your plants to grow securely
- Grow small cool-season veggies
- Harden off younger plants before outdoor planting
It is important to know you should build your cold frame roof with a pitch/slope to allow for rain drainage and stop water build up to help keep your fruit and vegetables warm in the colder months.
Cold frames are the preferred choice to use in the winter as structures such as portable greenhouses are not robust enough past summer. On the other hand, cold frames are durable enough to stay up all year round, especially when constructed of a robust material like polycarbonate sheets.
Advantages of a Cold Frame:
There are four main advantages to using a cold frame greenhouse rather than other structures:
- Cold Frames let in sunlight to encourage plant growth
- Retain warmth creating enhanced plant growth climate
- Lower cost than a Greenhouse or Polytunnel
- Suitable for small gardens
What are the best plastic sheets to use on a cold frame?
Polycarbonate sheets are the best plastic sheets for cold frames due to their durability, clarity and UV protection. The most common types of polycarbonate include:
- Axgard Solid Plastic
- Axiome twin wall polycarbonate
- Corrapol corrugated plastic
Using polycarbonate sheets is very straightforward as they can be cut down easily to any desired size, for you to build a bespoke size cold frame.
No matter whether you choose solid or twinwall plastic, you want to use clear polycarbonate sheets as they let the maximum amount of light in. It depends on what you are growing but 9 out 10 times the lighter the more optimum the growing conditions. Particularly in darker winter months!
For lower light transmission you can also choose Opal polycarbonate, which reduces heat absorption, or Bronze polycarbonate, which increase heat retention, but these are far less common.
It is worth pointing out that although glass seems like a good option for light transmission, it is likely to break easily and also is very costly which makes it unusable for this application.
Which type of polycarbonate sheet is best for a cold frame?
When building a cold frame DIY there are two main polycarbonate sheets to choose between: twinwall and solid polycarbonate. Both are excellent sheets to use but suit different objectives.
A honeycomb-type structure gives multiwall and twinwall polycarbonate the edge when it comes to heat insulation, a key factor for cold frames.
Within the Axiome twinwall range, the 10mm polycarbonate tends to be the most common thickness to use for creating a wooden cold frame as it offers a good mix of flexibility and strength for when you are on a budget.
If you have a moderately bigger budget then upgrading the 16mm polycarbonate is a good route for increased strength and insulation.
Alternatively, you could choose solid polycarbonate which has the best light transmission and is extremely robust. The downside of fitting a solid plastic is that it has lower insulation levels, however, this may not be a concern for colder-weather plants.
Think about what you are most likely to be growing before making the choice!
It is important to purchase the right sheet for your cold frame greenhouse as failing to get the ultimate sheet could prevent your plants from being fully developed.
| Solid Polycarbonate | Twinwall Polycarbonate |
| ££ | £ |
| High Transparency (Similar Visual to Glass) | Medium Transparency |
| Medium Weight | Lightweight |
| Low Insulation | Medium Insulation |
Can you use corrugated plastic for a cold frame?
Yes, corrugated plastic is not normally used for cold frames, as it doesn’t have the same insulating structure as twin wall or multiwall sheets, but this doesn’t mean that you cannot use them!
Corrugated plastic sheets are one of the more budget friendly sheet options and could be used for when you require lower levels of heat retention.
How to make a cold frame?
Cold frames can be set up on just about any surface, including grass, concrete or a gravel base. It is best to have a solid base for tidiness and keeping the garden frame structure stable.
They can either be built in or can be made to be easily moved around, so you can choose where is best depending on the shade or sunshine you desire for your plants.
Timber is the traditional choice for constructing a frame and the most popular due to being quite low cost. The part that matters the most for lifespan is what plastic sheet you use and how you fix them into the wood.
How to build a cold frame to suit your garden design?
The essential components you will require to create the ideal cold frame are:
- A solid gravel or slab base
- 10mm or 16mm polycarbonate
- Alukap-XR End Stop Bar
- Alukap-XR Gable Bars
Alukap-XR glazing bars are the ultimate fixing bars for your cold frame as they are manufactured from aluminium. These bars offer excellent weather resistance while also ensuring a stronger fix for the glazing. Pair this with polycarbonate and you have got a cold frame that not only looks amazing but will last 15 years due to its impeccable strength.
Using this aluminium capping reduces the amount of exposed timber on the top which will rot over time and break down. The aluminium glazing bars provide unbeatable robustness against the elements!
To create the lowest cost cold frame possible, you could substitute the metal components for Snapa Drip Trim around the edge of the sheet. This method requires the frame to be the fixing method so more complicated than screwing the aluminium bars simply to the frame.
What are the best plastic sheets to build a Cold Frame?
To build the ultimate cold frame you should use 10mm polycarbonate sheets. It is a quality material that is incredibly strong and durable; just what is required for a cold frame.
If you are on a budget then twinwall is the most cost-effective sheet, it is lightweight and has superb light transparency.
Need Help with your Cold Frame Project?
Please contact us if you have any further questions with our plastic sheet range. Our Live Chat Teams are always happy to discuss any questions with you. Alternatively, you can contact us where our Teams will provide you with all the advice and support you require for your projects.
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