At this time of year, daylight hours are hard to come by; there are less than eight of them around the time of the winter solstice in late December. Many edible crops grown in glasshouses, such as tomatoes, need more daylight than is naturally on offer, leaving growers with little option but to use artificial lighting to shorten the night-time period.
This can be a very expensive exercise in the depths of winter, so many of the glasshouses used to produce food crops stand dark and empty at this time of year, which means that UK demand for tomatoes and other salad crops is usually met by imports.
However, as I mentioned in a previous column, our tomato crops here at Stockbridge Technology Centre will be going strong all winter, thanks to the extra light provided by LED (light emitting diode) technology, which illuminates the crop at very low cost.
We use mainly red and blue LED lighting to grow our tomatoes because they are the two colours of light that plants respond to best. This gives our glasshouses a very festive feel at this time of year – they certainly outshine the single string of Christmas lights in my window at home!
Our work with lighting and crops is led by head of photobiology Dr Phillip Davis, and also extends to other areas. By tweaking the combination of colours and the intensity, duration and pattern of light that our crops receive, we can deliver exciting results, particularly in our urban farm facility, where we have complete control over the levels of light that crops receive.
If you want to learn how to produce a really aromatic basil or grow a more compact bedding plant simply by tweaking the levels of light they receive, Phil is definitely the man to talk to.
We’re even beginning to discover how we can use light to help control pests and diseases in our crops. This is welcome news for growers everywhere and a technique that can be applied to garden greenhouses just as well as it can to commercial glasshouse facilities.
Preliminary work by James Townsend, another member of our team here at Stockbridge Technology Centre, suggests that we may be able to control certain diseases simply by switching the greenhouse lights on for a few hours during the night. So, if you’ve been asking yourself how to get year-round use from your greenhouse or grow more flavoursome herbs, or whether there’s an easier way to keep pests and diseases at bay, the future, if you’ll pardon the pun, looks bright.
What’s the word from our weather station?
As expected, during the first two weeks of December temperatures continued to fall; there was snow in many parts and frosts became the norm.
Our weather station recorded a grass minimum temperature of -18.5°C on December 12, with maximum air temperatures only nudging into double figures twice before the fifteenth of the month. Though early December occasionally brought us bright skies (there were more than seven hours of sunshine on the eighth), we had an average of less than two hours of sun per day between the first and tenth of the month.
It was good weather to be a tomato plant at Stockbridge Technology Centre – snug in a heated glasshouse and bathed in the red and blue glow of our LED lights.