We heat greenhouses to keep tender plants safe through winter and start off outdoor plants earlier. In my last piece I noted how we could save on that heating by maintaining good air circulation with low humidity. These conditions reduce mould on our plants, something surer to kill than the low temperatures themselves.
However keeping the temperature sufficiently high is still the most critical factor. Heating is inevitably expensive and adds to our Carbon loading so we add insulation.
Double glazing by fitting plastic sheeting or ‘bubble-wrap’ on roof and walls cuts the heat lost considerably. Further reduce draughts and heat loss by fitting a sheet to cover the door, make this so it can be held aside as you go in and out. (Handily clothes pegs will often hold insulation in place or temporarily out of the way.)
But there comes a huge problem with adding insulation and that is reduction in light. Just a film of dirt left on the glass will diminish the already pale winter sunlight. A layer of insulation more so. And this reduced light means our plants are less able to photosynthesize and grow. The tougher plants may just sulk but many will suffer and show this with paler leaves and spindly growth. Seedlings particularly respond by becoming etiolated (straggly), as they strive to find brighter light.
The answer is give them artificial light. Now this used to be very expensive as ‘ordinary’ household lights were not suitable (wrong mix of wavelengths) so special lights were needed expensive to buy, and expensive to run (though they did save on heating as some ran really hot). Fortunately newer LED lights are much more efficient, and both less costly to buy and run.
I cannot emphasise the difference adding extra light will make, especially to real sun lovers such as cacti and succulents. Actually all your plants will be happier, and new sowings made early in the year become better than you’ve ever grown before. That extra light makes them squatter, bushier, darker, and earlier to pot and move on.
Indeed it’s now almost essential to add LED lights as they’ll make such a dramatic difference. Plus, their bright light may make you feel better as well.
So win, win.