How To Insulate Your Greenhouse

If you’re worried about your fennel freezing or your fuchsias getting frostbite, then making sure your greenhouse is insulated for the winter is a gardening essential. There’s no need to worry about expensive installation or specialised materials, either, as this is a DIY project that most amateur gardeners can achieve with ease. Read on to find out how to source and fit your own insulation, for an inexpensive but highly effective way of protecting your plants and vegetables during the winter months.

To prepare your greenhouse, first make sure the glass is cleaned thoroughly. This will maximise the amount of light available to your plants, particularly when you begin to add your insulation materials. It’s also wise to check there are no broken or cracked panes. If so, replace where necessary, tape over cracks or use foam sealant to run along the edges of the panes for a secure, draught-free seal.

Thankfully, there is a very beneficial but cost-effective method you can choose to provide the insulating layer of warm air that’s needed to maintain a good temperature in your greenhouse. Bubblewrap, commonly used for protecting packages in the post, makes an excellent insulator and the larger the bubbles the better, as they let in more light and provide a better barrier from the cold. Bubblewrap is available online in large rolls (50m usually costs on average between £15-20) from online packaging suppliers or by the metre from garden centres. Some garden supplies websites also supply fixing plugs and offer calculators to help you work out the amount of insulation you’ll need.

If you’re confident with doing this yourself, first measure the height of the greenhouse walls and cut the bubble wrap into lengths, fixing to the frame using clear, all-weather tape (small nails or a staple gun could be used if your greenhouse has a timber frame). Make sure there are no gaps, as this will allow in cold air and spoil the insulating effect. Next, it’s time to cover the roof – try getting in a friend to help with this and make sure you leave access to the opening windows, should you require some ventilation when working in there in the winter. Attach the bubblewrap to the centre ridge then run down the length of the roof until you meet the top of each wall. Repeat until the whole of the inside is covered.

When the greenhouse is fully insulated and the weather is clear, you will notice a discernible difference in the internal temperature and that will provide a nurturing environment for your precious plants. Another money-saving feature of this DIY method is that, removed and stored carefully, the bubblewrap can be reused for several years of frost-free gardening.