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Medwyn Williams

Hello. I'm Medwyn Williams – eleven times Gold medal winner at the Chelsea Flower Show, Past Chairman of the Royal Horticultural Society Fruit Vegetable and Herb Committee and President of the National Vegetable Society.

Planting leeks and onions into their final pts


I had rather a busy time last week which was a good thing after having hardly done anything over the festive season. The Peter Glazebrook onions were all transplanted out into 60 cells a fortnight ago and I finished doing all mine last week.  The Leeks that I had struck from bulbils during the middle of August, with the intention of staging them at Chelsea, are really doing well now. The onions were also sown during mid August for the same reason.  However as I have pulled out of Chelsea owing to a lack of sponsor I am now concentrating on staging a display at The RHS Tatton Park Show.

The gamble I have taken is that the Pendle Leek, the Cumbrian Pot leek and my own selection of Kelsae onion, will hold until the middle of July before bolting. I decided therefore last Thursday that they were all going to be planted up in their final pots.  The 32 onions were planted in 25 litre pots and the 17 Pendle leeks  went into 30 litre ones. The reason the onions were planted in 25 litre pots was to able to fit them all on to the same bench.

The Pendle leeks will now be left to establish themselves before I put my first nine inch collar on them. The six pot leeks were planted up in a bottomless 5 litre pot on top of a 30 litre one.  A sort of ring culture system that allows me to harvest the pot leek and the bottomless pot and re potting them into another proper 5 litre pot. This way I can stage them as if they had been grown in that pot throughout. The mix was – 70 litre bag of Levington M3, 20 litre pot of sieved soil that came from my celery bed and stored in my polytunnel to dry out. Finally another 10 litre of Vermiculite was added to open up the mixture and to allow more air in and around the root system.

This was the maximum volume I could get into the mixer, added to the whole mix was 100 grams Medwyn’s Osmocote Exact Standard 5-6 month release with an NPK of 15+9+12. This should make sure that the plants will never be lacking for nutrients and they should grow away without having any stress which will hopefully prevent them from bolting too early for me. Also added to the mix was 100 grams of Nutrimate powder to ensure the roots are best able to partake in all the nutrients available to them.

Watering is critical when growing in pots in this manner, and particularly on a bench where they can’t root into any other medium.  They were given a fair amount to begin with to make sure they were well bedded in, from now on they will only be watered around the inside of the pots rim and never over the plant in the centre.  I will keep you informed as they grow on.

Towards the back end of last year I had a terrible infestation of White Fly and I have now managed to keep it well under control.  The main way was by using large size yellow sticky traps with a grid marked out on each in inch squares. You can clearly see how bad it was and by laying the sticky tarp flat on some pots, rather than hanging them, they do a better job.  The thinking is that the fly has to drop down at some point and the larger yellow surface area will attract them faster than the foliage or a hanging trap.

Pot Leeks Cumbrian in two pot system just planted in Aber in 30 litre pots.
Own selection Kelsae onion seedling just moved to 60 cells.
leeks Pendle just planted up in 30 litre pots in the greenhouse at Aber for Tatton Park Show mid July.
onions just planted up into 20 litre pots 030113




Growing Parsnips

25th July 2007 I am often asked what is the best method of growing both long carrots and parsnips for the show

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12 thoughts on “Planting leeks and onions into their final pts

  1. Looking good Medwyn. I seem to have lost all the previuos articles of your blog though and i think it’s the same for everyone??



  2. Happy New Year Medwyn, can I ask what mix you use for potting on your onions at the 60 cell stage?

    1. Hi John,

      The mix I use for the 60 cells is Levington F2S and I use the Imidiacloprid insecticide powder to the mix to control all the pests, its expensive but does the job well. I’m sure you can buy it as Pravado.

  3. Thanks Medwyn, a useful tip. The centurion onion sets arrived safely, excellent quality as always. Do you think that the shape of the onion set in any way reflects the final shape of the onion. Last year was my worst year with Centurion which I put down to the lack of light but thankfully none went to seed which fingers crosss seems to be a feature with Centurion even though I assume your sets are not heat treated. I shall plant in pots back end of February and plant out early to mid April.

  4. Hi Medwyn,my leeks are probably the same size as yours and im thinking of setting mine into 35 ltr pots.i know a lot of the top growers grow in pots but is it possible to get size and quality for my show at the end of July.thanks

    1. You can most certainly get leeks of really superb quality for the end of July if they are the same size as mine are now. I have had some super leeks from 30 litre pots so a 35 litre pot should be even better. Depending on the mixture in the pots you will probably have to liquid feed a little as the pots really get full of roots as the leek develops. By the way, my leeks are grown in the University glasshouse where the temperature is 16 degrees C during the day and 14 degrees C at night with lights on for 16 hours per day, they are fixed and I can’t alter them.

  5. Hi

    First time post on this site, you mention you are growing your leeks in 35 ltr containers, are these pot leeks and if so what sizes are they producing when benched.

    Regards Steve

    1. The leeks that I have had success with is the Pendle and Welsh seedling, both blanch leeks. I have had them 9 inches in girth and over 18 to the button. I can t see no reason why you can’t grow good pot leeks using the same size pots, But I haven’t personally grown them.

  6. what lights do i need to grow leeks and onions under

    1. There are different types of lamps available now from Fluorescent tubes to 400 watts Son T Aggro lights. The latter one is the type that I have used, primarily becuse its the lighting system that Bangor University has at the glasshouse in Aber near Bangor. Some of the top growers seem to manage very well on 6ft tubes in banks of perhaps 4 to 6 double units. The beauty of the tubes is that they don’t pass on too much heat so that you can lower them right on top of the plants. We are at the moment experimenting with an electronic company to introduce some New LED lights. These are definitely the way forward but we will have to see how good they are this coming year before we sell any on. They are not too expensive to buy and cost pennies to run and guaranteed for some ten years.

  7. how do I couler after the 18″x4″drainage pipe

    1. I’m not sure why you would want to collar after the 18 inch collar as it could be sufficient as you will normally have at least an inch of the leek below the soil or compost level. However as you are growing in pipes you will need to wrap some builders damp course around the outside of the pipe and three inches higher which would then give you more length. Growing them in pipes is not the best way as you are very likely to severely damage the flags as you lift the pipe up to see what the condition of the leeks are like. Nex year try using builders Damp course cut into different sizes from 9 inches to 21 inches in stages of three inches.

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