Welsh Emblem - The Leek
19th Jan 2000
The mixture that is use for both the leeks and the onions is mainly peat based but from this stage on I start to introduce soil as well. This will be soil sieved from the leek beds and stored in bags under the greenhouse staging so that it is always at the same temperature as the plants are growing in. The mixture now will be 3 parts Levington M2, 1 part of the sieved soil and 1 part vermiculite. With vermiculite it pays to moisten it slightly first so that when it is mixed with the other elements it doesn't soak up too much moisture causing the compost to dry out too much.
I have found this compost to be very beneficial towards producing strong root growth and this is the most important element that you have to gear yourself up to. Without a strong active root system you will have small struggling plants, so do take care to make sure that everything you do is towards producing strong clean white roots. Once you have a good root system the top will look after itself.
The plants at this time of year will obviously need warmth and in my case this is given through my Parwin electrical heater with the thermostat set at 60° F. The leeks are grown at this stage inside my temporary growing cabinet which is made from some lightweight battens covered over with panels of hardboard. The inside of these panels have been covered with a reflective material to make sure that the light inside the cabinet is reflected to every corner of it and at equal Lux levels. (Lux being the measurement unit of light) The reflective material that I use can be bought from any good DIY store and is made from eighth of an inch thick polystyrene covered over with aluminium foil. It is made primarily for reflecting heat from behind radiators etc., but I have found it excellent for reflecting light as well.
The base of the growing cabinet has first been lined with polythene on which an electric blanket is laid which is again covered with polythene, this in turn is covered over with 3 inches of sand. The temperature underneath the plants is kept at about 70° F and always moist, a very important point as the moisture is the key to good heat distribution along the bench. Whenever you are in the greenhouse keep an eye on the moisture content of the sand and always add more water when necessary. For this job I use water that's stored in a barrel at the end of the greenhouse so that it doesn't drop the propagating temperature too much.
The bench is the whole length of the greenhouse which is 12 foot and the width of one side which is 3ft 3inches and this whole area is served by one Philips SGR luminair fitted with a 400 watt SON T aggro lamp. The question of how many hours of artificial light to give the leeks is an interesting one because after a chat with fellow grower Ken Davies from Wrexham, he is convinced that too much light too early on in their growth can be responsible for the yellowing of the barrel that can so devastate perfectly good leeks.
I had a slight touch of this last year on two leeks while Ken's were more or less rendered useless for exhibiting. This problem can affect both blanch and pot leeks and the yellowing can occur just under the button on the barrel or as a streak straight down the barrel. If you remove a flag to try and get rid of it you will notice that it's still on the next one and probably right through the plant.
What causes this problem is still not known but Ken may well have a point that we are definitely pushing the plant over and beyond their limits and this might be the plants reaction to over photosynthesising. I really don't know and I would like to hear from other growers who have experienced this and more importantly if they have overcome it. On my part I intend to reduce the lighting period from the 24 hours that they used to have to 16 hours. This is based on the hours that the commercial greenhouses at the University in Bangor are set and where I grow my vegetables for Chelsea. In the five years that I have grown leeks there in pots, I have never had a trace of yellow on any of the barrels. I just wonder.