NEW LIGHT ON COLD FRAMES
This month has been full of revelations for me. I had not realised there is a fantastic glass substitute out there – ETFE (short for Ethylene tetrafluoroethylene) film – it is the same price as horticultural glass, is far more durable and allows the full spectrum of natural light through. Now, excitingly, it is just becoming available for gardeners, rather than just commercial growers.
Phillip Lee, founder of Ripe (ripehouse.co.uk), offered to fit some ETFE film to three old Dutch lights (bought second-hand about 30 years ago) that cover my cold frame. Lee designed and built the first ETFE greenhouse during his PhD research in the UK in 2006, and recently built the Natural Light Growing Centre at Warwick
University to study the effects of plant growth under ETFE.
Once again, the glass in my cold frame had been smashed in a storm (by apples from a tree), but Lee assured me the ETFE would easily cope with apples bouncing off it. If it does get a hole in it, it stays that size and does not spread. You can cover the hole with some special tape.
Another reason for its appeal to me is that ETFE is self-cleaning: moss, algae, dust and bird poo debris just will not grow or settle on it. When you grow under glass or poly, this debris drastically reduces the light levels, which stresses the plants and causes them to grow in an etiolated way. Plants grown under ETFE are stronger, with shorter distances between their nodes and, in trials, the produce has been convincingly shown to be more flavoursome, with a higher vitamin content; crop yields potentially increase by five to 15 per cent. Finally, plants grown under ETFE do not need as much hardening off before planting outside, as they are already getting exactly the same light spectrum undercover as they would outside.
ETFE has a lifespan of 20 years minimum, but architects often quote 50 years. And it is completely recyclable and reusable. There are two types of film, clear and opaque, and they are both amazingly thin – 100 micrometers – similar to a sheet of thinnish paper. I tried to manually rip a sample, but could not.
Lee strengthened the wood on my old frames as best he could (the film needs to be taut), then covered them with the film. Inevitably there are a few minor ripples, but the newly clad frames are now snugly in place and I am putting trays of seedlings for my new rose meadow inside (see above right), plus trays of cuttings and vegetable seedlings.
The film does appear slightly more opaque than the old glass; this is because there is a naturally inherent light diffusion, which is beneficial to plants. The insulation value of a single layer of ETFE is slightly better than standard 3mm horticultural glass, but, when used as a double layer, it is significantly warmer than glass.