Method of Propagation - Leeks
28th Sep 2000
If you want to start off next year with your own stock of leeks, then you must start now by selecting a few of the best blanch leeks that you grew this year. Growing leeks for exhibition is very rarely carried out from sowing seed as the end product will be variable so most, if not all, leeks that you see on the show benches have been propagated from bulbils or pips. These are actually miniature little leeks that grow from the leek seed head and are effectively a form of cutting from the mother plant. This means that not only are you able to start off with a relatively strong plant, the end product will very uniform as well.
Pips or Bulbils
The way of getting these pips or bulbils is to keep the best leeks that you had at the last shows or those that you will be exhibiting shortly. Best doesn't necessarily mean the biggest, you should look at the leek in the same way as a judge would look at it on the show bench. It should have a length in excess of 150mm to the button with good balance between barrel length and circumference. The barrel should be straight with no sign of any bulbousness around the bottom and should be as parallel as possible.
The reason for selecting such specimens is to make sure that because of the method of propagation, we don"t end up producing specimens that carry over genetic faults that are in built in the leek. Most faults are often cultural such as ribbiness and barrels that are bent, so those faults would not be carried over to the next generation of plants. However any bad bulbousness around the root plate, although often considered to be a cultural fault, can also be in the genetic make up of the leek and therefore those leeks are best not used for propagation purposes.
Once you have selected a leek, trim off the current years roots as they will only rot away when re planted and cut through the barrel approximately six inches above the root plate. This means that you can have the best of both worlds by keeping the small barrel with the root plate for growing on whilst the remainder of the barrel can be eaten. The next step is to remove some of the outer flags or skins from the leek until the diameter of the barrel is approaching the diameter of the root plate. The removal of the surplus foliage or flags will leave a strip of flesh around the leek just above the old roots, from this area the new roots will emerge and these are the ones that will sustain the plant right through to next November when you will be taking bulbils from the new head.
At this point cleanliness is vital as you don't want to risk any disease spores settling in around the root plate and possibly being carried right through the plant and into the off shoots next year. I have had no problem at all with my leek bulbils with disease for many years now and a lot of it is attributable to maintaining a clean regime throughout the plants life. Just before planting the leek stump, I will leave them to soak for a couple of minutes in a strong dilution of common household bleach. This will makes sure that any disease spores lurking around the root area will be killed, I have also noticed that the plant makes a stronger rooting system as well.
Compost and Temperature
Plant the leek stump either singly or in multiples with the pot size then depending on how many you intend to plant per pot. Over the past few years I have had better results by potting each one separately in a 2 litre pot using Levington M3. Make sure that the root plate is about two inches below the level of the compost and during it's initial rooting period it should never be allowed to dry out, neither should it be saturated. If you are going to take some leek stocks from now onwards, the night temperatures will be getting lower and rooting becomes more difficult, so it will pay to keep them indoors for a month or so and afterwards outside.
Keeping the leeks from throwing pips or bulbils too early is not easy, ideally we want to be propagating bulbils that are fresh and green next November so in order to try and achieve that, they must be kept growing at a low temperature. Ideally you want to position the leeks somewhere where there is some shade and where there is also a cover overhead to prevent the pots form being saturated over the Winter months. The exhibition leeks that we are growing today are certainly not as frost hardy as some of the ones from seed, so it is wise if we have any prolonged period of frost to move them indoors.
Cold Frame and Polytunnels
My stock leek are looking well at the moment and I just hope that they will maintain this excellent condition until I require them from late October onwards. Up to now the stock leeks have been standing outside in my cold frame and in order to prevent the heads being saturated with rain, with the possibility of premature rooting of the bulbils, they will be moved into one of my polytunnels and the heads and stems given a spray with an insecticide and fungicide to maintain a clean healthy stock.