Growing food - Keeping plants warm at night using Christmas lights
Like many gardeners I like to extend the growing season. The challenge, of course, is to provide young plants with favorable growing conditions in our undependable climate. Spring weather is unpredictable, and those warm, sunny days in March and April are deceiving. In my garden on southern Vancouver Island cool, wet conditions are common in May and June, even if early spring months are mild. While it is tempting to set out plants early they can easily be set back and often these plants do no better than those that are placed in the ground later in spring — once the soil has really warmed. In the same way, most seeds need warm soil to germinate and will often rot in cold wet soil.
However, with a cold frame or a hoop tunnel or a greenhouse, a gardener can jump start the growing season. Here is how I do it.
The first photo shows my greenhouse at night. Yes, I suspect the neighbors debated calling the fire department when those lights switched on for the first time, but I think it looks very cheery. Right now I have basil and tomatoes in the greenhouse so my thermostat is set to 13C (Photo #2). When night temperatures fall below 13C the backyard lights up and the incandescent bulbs produce just enough heat to keep my plants cozy under their Reemay blanket (Photo #3). The thermostat is a commercial model and is well built. I have the thermostat set so it turns on when the temperature falls below the set point. The same device can be easily rewired to turn on when the temperature rises above a set point and this could be used to cool a greenhouse, by switching on a fan, for example.
If you are not familiar with Reemay floating row cover, it is worth a look. The fabric is light, can be easily cut to size and allows approximately 75% of the sun’s light to pass through. Reemay is also used as a barrier to keep insects off crops but this requires a tight seal all around (Think carrot rust fly or cabbage butterflies or…). If you are using it to protect plants from frost you can double it up. I use large binder clips to clamp it onto the supports and bricks (naturally) to anchor the bottom of the fabric. WARNING — make sure you don’t let plants overheat when the sun comes up, and that can happen very quickly. Says someone who has forgotten to open things up in the morning.
The Christmas lights are ‘old school’ incandescent lights and are getting harder to find. Garage sales, second hand shops and your friend’s basement are likely sources. LED lights won’t produce the gentle heat you are looking for. And, as always you need to think safety first — watching for bad wiring and using common sense when running extension cords outdoors. Always follow outdoor electrical precautions.
A maximum-minimum (or min-max) thermometer is a valuable piece of equipment for any gardener growing in a cold frame, hoop house or greenhouse. (See photo #4). My max-min thermometer was not expensive, unlike the thermostat. You can see the “minimum” scale on the left. The upper arrow shows that the temperature dropped to 13C, but no lower because of those Christmas lights! The bottom arrow on the left shows the temperature in the greenhouse is sitting at 24C. The right scale shows the maximum temperature reached since the thermometer was reset…slightly over 30C. Fortunately I was around to provide some ventilation at that point. I normally reset the thermometer each day when I check it; the reset button is visible between the two scales. Simple technology but very useful.
The fifth photo shows the basic setup. Not pretty but very functional. I have set this up in my greenhouse because I just want to keep my plants warm and there is no need to heat the whole space. A similar arrangement would work well in a cold frame or hoop tunnel. I usually have the thermostat located more centrally.
Normally I take everything apart once the plants are in the ground but last year I left the lights up to provide late season protection for my peppers and basil (Photo # 6). And that is a quick summary of how I keep my plants warm at night using Christmas lights. If you have questions or comments feel free to post them below. I will try to respond in a timely manner.
‘TIll next time. Burl