Medwyn Williams explains why it’s OK to turn down the heat in the greenhouse
Dial down the heat Setting your thermostat a degree cooler saves on heating costs, with little impact on growth rate
December was a very wintry wet month on the island here, with only a couple of nights of hard frost to worry about and not a flake of snow. We’re extremely lucky on Anglesey as the Snowdonia mountain range seems to prevent most of it coming over. When it’s freezing hard it’s always a constant worry regarding the heating system, as the plants, particularly the exhibition leeks and onions, certainly don’t want a check to their growth pattern. Our heater is run on central heating oil, with a blower pushing the heat out and the temperature controlled with a very accurate digital thermostat.
Both the leeks and onions are quite hardy and they’ll grow on, though at a slower rate, when the temperatures are quite low. I set my thermostat normally at 14C (58F) but when it’s freezing I drop it down to 12C (53F) in an attempt to save on the oil. When it’s freezing a drop of a degree in temperature not only saves on the oil but also stops burn out on the machine. Setting higher temperatures costs a lot of money in order to gain more growth.
For those of you running electric fan heaters the same rules apply. Drop the temperatures down a bit on the coldest nights. Also check your electrical points to make sure that they’re all working correctly. I remember many years ago checking on the heating in the greenhouse in the morning, particularly the power plugs, only to find that I could hardly touch the plug as it was so hot. After I switched everything off for a few minutes I pulled the plug out and unscrewed it to find that the small brass screws tightening down the live wire were loose. It does pay to check on the wiring to make sure that every wire is screwed down tight and the proper fuse inserted.
Naturally, when I start off some of the more tender plants, such as tomatoes, chillies and peppers, I’ll set the thermostat at 15.5C (60F). Whatever the temperature you’re running at you definitely need to have a max/min thermometer in order to control the heating properly and to know how high or low your temperatures were during the day and night.