Making the most use of the heated aluminium greenhouses
13th Jan 1999
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Heating the greenhouses
At this time of year my attention is focusedon the two 12ft by 8ft heated aluminium greenhouses, both are getting quite full already as the leeks and the onions are regularly being potted on. If you are heating your greenhouse using an electric fan heater, do spare a moment to check the wiring and the plugs,particularly after a night of hard frost or snow. These heaters work overtime when the temperatures are consistently low and you will be surprised how hot the actual three pin plug gets if you put you hand on it. If the plug has been on your heater for a few years it's a good idea to replace it with a new one making sure that the wiring are really screwed down tight in the pins.
Both of my greenhouses are heated with the traditional Parwin three kW fan heaters and I say traditional in thesense that they have hardly change their design, to my knowledge, in over twenty years since I have been using them. I can"t talk highly enough about this heater, it's not a glossy fancy unit, rather a practical and reliable heater that does the job with the least hassle. The other great advantage is the fact that should anything go wrong with it, the parts are simple to get direct from Parwin and anyone witha little knowledge can easily replace them.
The leeks and onions are really motoring away now and with two Philips SGR lamps overhead in the twelve foot long growing cabinet they really seem to be responding to this extra light. Having had the experience of growing most of my vegetables for Chelsea at the University complex at Bangor where the lighting period there has been worked out to gain optimum growth from plants at the most economical financial outlay. This they proved worked out best when the plants were given a constant 16 hours of light right through their growing period.
Of course when you have bright sunny days the lights don't come on at all as they have the benefit of computer technology, but it has proved to me that perhaps we are wasting too much money, on onions in particular, by giving them a twenty four hour constant light period for six weeks. This year therefore, both the leeks and the onions will be given a constant 16 hours growing period through to planting out time, which in the case of onions will be around the middle of March. Prior to this, the beds will have been thoroughly prepared and thermostatically controlled soil warming cables positioned between seven and nine inches down in the soil. This means that the soil will be at least 55°F at planting time giving the onions the best start that they could possibly have.
Warming up the Soil
One word of caution here, if you are not prepared, for one reason or other, to warm up the soil prior to planting, then you are much better off potting the onions on around the end of February into perhaps six or seven inch pots with a view of planting them during late April when the soil underneath the polythene cover will have warmed up sufficiently to maintain growth. Trying to force onions to grow in unsuitable conditions will only lead to a disaster later on with possibly a number of them going to seed. Always bear in mind that if the soil isn't at the correct temperature when planting, the onions will just sit there trying to acclimatise to the much cooler environment diminishing totally any gain that you thought you might have had through early planting.
Sowing the vegetables
There are two vegetables that I like to sow at this time of year, one is the parsley and the other is onions for the under eight ounces class or 250 grams if showing under NVS rules. The parsley variety will be Faulds and Frison, the latter being a newer variety from my own seed catalogue. I like to sow the parsley early as it can be quite difficult at times to germinate, cover the seed over lightly using some fine vermiculite and keep the growing medium uniformly moist all the time. The tray in my case will be kept on the greenhouse bench where I have some bottom heat through soil warming cables. If you have no warming cables then the germination rate would be vastly improved if you can make use of an electric propagator.
The small onions are broadcast sown in half sized seed trays using Levington F2 and again covered with about ¼" of fine vermiculite. I find since using this material to cover the seeds, in preference to the sowing compost, that the germination rate is much more even with the young seedlings able to push their heads through the vermiculite with ease. Do make sure however that when watering the top of the tray, that the first time, you use a very fine sprayer as the vermiculite is so light that if you use a watering can the materialwill move all over the tray.
The varieties that I intend to sow are going to be Toughball and Bison, both of these have proved themselves on the showbench at National level, but I have to say that my preference is for Bison, provided I can grow them as good as Ron Macfarlane from Pembroke seems to able to, it has a beautiful deep brown colour with a much more pronounced veining in the skin than Toughball which really catches the judges eye.
Both of these varieties are for sale in my catalogue, both as seed as well as strong young seedling plants which will be ready for posting in stout cardboard boxes during late February, weather permitting.