Artificial Lighting in the Greenhouse
28th Nov 2002
I have heard some growers say, 'why should I bother with using artificial lights in my greenhouse, I can grow perfectly good leeks and onions without them'. My stock answer usually is that I could also grow perfectly good leeks and onions without lights but they definitely wouldn"t be as good as those that I grew with lights. The strange thing is that those who say they grow well without using them are never at the very top when it comes to staging at national level.
There's no doubt about it that the use of artificial lights in the greenhouse has improved both the quality and size of our leeks and onions. Does anyone seriously think that Mel Ednie would have won the world record with an amazing onion weighing 15lbs 15½ounces without lights - never. The fact is that Mel's onion is going to hold the record for a very long time to come yet, when you think of the number of top growers that are trying very hard indeed to beat it and they haven't come within 3 lbs of it yet, it says a lot. Of course it wasn't artificial lights alone that won the record for Mel, it was a series of things, he had the best seed, he had also just changed his soil, the Spring weather was nice and warm and though we had a hot sunny Summer Mel had the benefit of living close to the sea with the breezes helping to keep temperatures naturally at a good optimum growing level.
Buying in Plants
You don't have to spend any money at all on growing onion plants yourself using lights, you can buy in some excellent young plants from growers such as myself which takes out some of the expense for you. However at the end of the day the sheer enjoyment of gardening for me is to start off from day one with seed, that is the real challenge and that is what real gardening is about. There's no two ways about it, if you want to grow your own top quality onion plants, then you to be prepared to spend some money, it's not cheap, but neither I'm led to believe is Golf and that's only another hobby!
To grow these onions these are the things you really need, You must have a heated greenhouse, it can be either gas, coal fired or electric. Paraffin heaters are also fine but you must be prepared to use the vents regularly in your greenhouse to get rid of some of the fumes. From my experience neither the leeks or the onions like to have the paraffin fumes around them and it inevitably shows up with the tips of the leaves yellowing and dying back. My preferred option is for an electric fan heater and I have two 3 kw Parwin heaters which are really well made, simple in construction yet really effective to heat both of my 12ft by 8ft houses.
The next thing you need is a good propagating bench which has a source of heating of either an electric blankest just sitting on top of some thick polystyrene panels or as in my case, a deep bed of sand with heating cables buried in it and thermostatically controlled. I have found these invaluable during the winter and early Spring as a source of germination, rooting of cuttings and numerous other tasks. Now we get to the growing cabinet, and what I have down is to incorporate the propagating benches and the growing cabinet into one unit in the greenhouse. I know of some growers who have erected a growing cabinet within their garage, shed and even in a spare bedroom. That is perfectly fine provided you make alternative arrangements when the plants want moving on.
The structure of my growing cabinet has been up many years now and is made from some light weight dexion which is an angle iron with slots and holes in it. The propagating bench runs the full length of the 12ft house, all along one side and is 3ft wide, so the framework naturally covers this area and is just over three foot in height above the sand. The next thing is to decide which lights you are going to use, whether they are going to be of a commercial nature and cost you a little extra or just good quality tubular lights.
In the past I have used both, separately and together, my preference at one time was for the Phillips SGR 200 unit with a SON T Aggro 400 watt lamp fitted. This was suspended from the ceiling of the steel structure and the tubes were positioned some 9 inches or so above the level of the sand and running lengthways along both sides of the cover. The idea was to have plenty of light above the foliage as well as having enough light being thrown in from the side at the stem of the plants to keep them nice and stocky.
I still use two of the above units spaced equally along the 12 ft length and I have noticed that if you change the lamp within the unit after about 2,000 hours of work, the plants will still remain nice and stocky. Be warned, if you are not prepared to change the lamp then you will find, like I did a few years ago, that you will have leggy plants with long necks as the quality of the blue light within the lamps spectrum diminishes. All that remains now it to be a good caring neighbour and not have everyone's garden floodlit at three or four in the morning. You therefore need to cover your plants; yes the above is one reason for doing it, but far more importantly is to retain as much of the lights within the actual growing area.
This is achieved by either covering over the cage like structure with black and white polythene, obviously white inwards, or as I mentioned the other week, cut panels to fit the framework which is what I am going to do. In the past these panels have been covered over with a silvery material on thin polystyrene that you can buy at your local DIY. However a friend of mine is now going to let me know where I can purchase some sate of the art far superior material. This material apparently was created by NASA and really bounces the lights within the growing cabinet hopefully giving you far superior and more even plants, time will tell and I shall certainly keep you posted. One last thing, whatever you use to cover the cabinet with, make sure that you have a way of ventilating it, the lamps give off a fair bit of heat and the temperatures can soon get too high in there.