Polytunnels & Electric Fans
8th Jun 2000
Polytunnels have undoubtedly become part and parcel of the show scene for some years now and where would be without them. They are reasonably priced and afford us the protection of growing top quality vegetables, not only earlier but to a higher standard as well.. Most onions and leeks for exhibition these days are grown in side them and there is no way that Mel Ednie would have achieved his phenomenal World record of 15lbs 15½ ounces without one.
They can however be like ovens from now on if we have a decent Summer and many of the ones over twenty feet in length must have some form of air flow to combat the incessant heat that can build up inside them. This week I shall be setting up my electric fan to make sure that there is plenty of air movement inside them. The fan itself is cylindrical in shape and is suspended from the polytunnel roof with chains and at an angle slightly above the foliage of the leeks and onions. They are reasonably cheap to run on electricity and with a time switch can be set to come early in the morning and off at around 7 p.m.
My leeks are now nearly ready for their 18" collars and at the moment I am reasonably pleased with them, I have 32 of the Welsh variety and 8 of the Peter Clark . At my friend Jims garden I have plated a further 30 leeks so that I should have plenty to select from.
My collaring techniques hasn't altered over the last ten years or so and consists of utilising square pieces of the black pliable builders damp course which is cut into different sizes thereby accommodating the length of the leek at different stages in it"s growth.
Normally I have a set of collars that I use from year to year made up of square pieces measuring 9" x 12" and 15" x 18" these two squares are usually sufficient for my needs. Normally the first square piece would be wrapped around the barrel of the leek to form a cylinder 9" tall and tied with string to a supporting cane, this would be done in the greenhouse when the plants were in their final pots. After planting out the collar would then undone and wrapped the other way around the barrel to form a cylinder 12" tall.
This year I planted out without any collars at all mainly having utilised the green plastic plant support clips to increase the length of the barrel bay wrapping it around the flags fairly high up thus ensuring that the centre of the leek is kept in the dark and therefore pulls upwards to the light. This has the effect of pulling or lengthening the barrel of the leek upwards whilst at the same time maintaining plenty of chlorophyll within the barrel. Currently the plants are now on 15" collars and attached to strong 3 foot canes which are pushed into the soil just behind each leek and about two inches away.
Throughout every stage of the blanching, care must be exercised that you don't extend the barrel too fast at the expense of getting some girth at the same time. Generally however if the plants were good ones going out into the beds and they were thoroughly prepared during the Winter then the process of changing collars regularly will ensure that you have a well proportioned leek. This week the 15" collar will be removed and turned around to form an 18" one. Before placing it back on every leek will be thoroughly examined and all yellowing or split flags will be removed.
As the leeks are planted with the root plate 3" below the soil surface, its important to ensure that any flags that are removed are cleared right down to the bottom of the barrel, not just down to soil level. At this time take a good at the barrel and if it is slightly bent then even pressure will bring it back upright. In this context I do mean slightly bent, if when straightening any leek and you notice the outer flags on the barrel are rippling then stop doing it. Effectively you have allowed the leek to grow without due care and attention and to the point where it can no longer be straightened and better left alone.
When clearing around the base of the leek remove any stones that you come across as these can press against the barrel and form an indent in it which can destroy an otherwise perfect leek. At this time of year I personally do not feed the plants as there should be plenty of nutrients in the bed. Later on though when the plants are approaching maturity they will have a high potash feed to harden the plant up.
Unfortunately the very fact that we now grow leeks under protection has increased the pest problem with Thrips being the main serious problem. Regular spraying should help and ringing the changes between Polysect and Malathion will help to keep the at bay. Another good method is to treat the plants on the basis that prevention is a lot better than cure. A number of leek growers are using Armillatox in this way by spraying the plants and the surrounding soil at every watering with a dilution rate of 5,000 to one or 1 ml to 5 litre of water. This will maintain the plants health whilst at the same time keeping the bugs at bay and giving the leek a deeper greener colour.