Vermiculite as part of Mixes and for Covering
23rd Dec 1998
Yes, it's that time of year again when it has become a tradition to sow your onion seed in an attempt to grow those giant specimens that really do bring tears to the onlookers' eyes. I have already prepared everything in advance; the compost, Levington F1, has already been inside the greenhouse for a few days to make sure that it"s up to the growing temperature. The vermiculite to mix in with the compost is also moistened and kept warm in the greenhouse.
I have used vermiculite as part of my mixes for both onions and leeks for a few years now and I find that I have quicker growth, probably as a result of a stronger root system as more air is able to get into the compost. My sowing mix is three parts F1 and one part vermiculite thoroughly mixed together.
A tray is loosely filled to the rim and levelled off using a straight edge. It's then lifted up and tapped down on the potting bench a couple of times. This is all the compaction that the compost needs; never press down with a flat board to the extent that the compost becomes solid as it"s not good for root development. I do use a small flat board very gently to flatten out any unevenness and to make sure that the seed will all be germinating from the same depth of compost.
Every seed is then positioned individually on top of the compost, making sure that each one has sufficient room for adequate development. This year I intend to use the Professional Seed Sower which picks up each seed individually and allows you to space them out accurately; the seed is then covered over with some dry fine vermiculite.
There is no doubt at all in my mind that vermiculite is best to cover the seed over in preference to the same compost in which they are growing. I have found that germination is much more even with none of the young seedlings failing to emerge as a result of their seed case being trapped in the heavier peat compost. This usually happens because the peat compost is more compact and the germinating seedlings haven't yet developed any secondary root system to anchor them down. Very often, when I used to cover them with the seed compost, I had many seedlings that seemed to have their whole root system exposed as the plant had apparently struggled to push itself out of the compost. Water the top of the vermiculite very carefully using a fine mist spray from a pump sprayer; don't attempt to do it with a watering can as the vermiculite is very fine, dry and light and will scatter all over the bench. You can cover the compost over in the traditional manner with a pane of glass and a sheet of paper on top or a piece of black and white polythene. For a few years now my preference has been to leave them uncovered, preferring to give a small light spray as and when the compost requires it. The trays are then placed in a propagator at a temperature around the upper sixties until the seeds have germinated.
Once germinated they are taken out of the propagator and placed on the propagating bench where there is constant bottom heat at around 65°F. My heated bench is part of my 12 ft long growing cabinet which is made from thin plywood which has been covered over on one side with aluminium backed polystyrene. This is the material sold at DIY shops for projecting heat from the back of radiators and it serves the same purpose inside the growing cabinet by reflecting rays of light from the two overhead Philips SGR lamps. The lamps are now left on for 16 hours a day with the time lapse being arranged so that the lamps are on to supplement daylight. I have found that the giving the plants 16 hours right through is just as good as giving them a period of 24 hours initially, I have proved this through growing my vegetables for Chelsea at University College, Bangor where their whole lighting system is switched off after sixteen hours and I found this to be sufficient for optimum growth.
Master Class Weekend
My Master class weekend for vegetable exhibitors went off exceptionally well with everyone that I spoke to having had a wonderful time learning new and exciting things about vegetables. There will be a similar weekend held next year at the same venue, Plas Tan y Bwlch in the Snowdonia National Park. If you would like to attend, please write to me for details as next year is bound to be over-subscribed.