Picture of Medwyn Williams

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.

Disaster with Leeks

Leek Pendle bolted early

Thursday 9th August

After using my first batch from a dozen Pendle Improved leeks for the Royal Welsh Display at Builth Wells I was left with a further 32 at Home that I was hoping to use in the Welsh Championships as well as in the National at Malvern.  That will not now be happening as well over half of them are bolting or going to seed.  I hate it when I open up the leaves in the centre only to find that there is no young leaf coming through, a sure sign that the leek is about to bolt.

It could be a combination of the fluctuating temperatures with far too much difference between day and night. They were also left in the pots a little too long prior to going into their final 30 litre containers.  The infuriating thing is that last year I was struggling to get my leeks to bolt for the production of bulbils, so I treated them dead rough. I gave them no water for days on end, kept them outdoors in low temperatures and they were kept so pot bound they must have been near to dying, yet none of them would bolt or throw up a seed head. Yet when given good growing conditions the buggers decide to bolt – that’s growing for showing for you.

One thing is very clear this year, the leeks that are left should be my best for  a long time as they are already on 7 inches around and 17 inches to the button. I made a deliberate effort this year to revert back to my old method of collaring the leeks earlier. In fact they were on 12 inch collars when still in 5 inch pots and I now know that the Pendle Improved likes to be collared early to extend the blanch.  Last year I wrapped 18 inch collars on the Pendle after leaving them too long on the 12 inch collars, they just would not lengthen and though very bulky I was lucky to stage them at just over 14 inches to the button.

Last November I was given a dozen young rooted new leeks from David Metcalfe, yet to be given a name, this is another of his crosses and looks like being a particularly useful leek for the Intermediate class if not as a blanch. This is a class for leeks measuring between 6 inches and 14 inches to the tight button.  Because of the above problems with the Pendle bolting, I may well have to revert to using these on my display stand at Malvern. They have now just had fifteen inch collars put on them and potted up to 30 litre pots using Humax John Innes N03. They are also around 7 inches in circumference but whether or not they will pull up in time in the next 7 weeks, time will tell.

Leeks Pendle all going to seed
Leeks Pendle on 18 inch collars in 30L pots


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12 thoughts on “Disaster with Leeks

  1. Good to know that even the best are suffering this problem. I don’t know of any grower who hasn’t had most of his/her leeks go to seed, from the south coast of England to the far north of Scotland. I planted 23 and at the last count 18 of them had gone. Very frustrating after seeing them through the Winter.

    Can you confirm that leek bulbils produced from leeks that have gone to seed in the first season won’t necessarily go to seed prematurely themselves?

    1. Hi Simon and John Ellis, The annoying thing about the leeks going to seed is that they were probably as good a lot of plants as I have grown. The reason they bolted for me though is not down to the weather, although it might have been a contributory factor, they were left too long in their pots before I found time to plant them in their permanent 30 litre pots. I now have 9 left which should be sufficient to cover my needs for the display at Malvern at the end of September. A few years ago now I remember a number of leeks going to seed then and I enquired with some of the lecturers at Bangor University as well as with Dr Peter Dawson of Tozers, whether or not leeks that had bolted could be used as Pips or bulbils in the same year. They both replied that you could use them and they shouldn’t go to seed the following year. I have to say though that I had enough pips that year so I never did use those that had bolted, so I really cannot confirm their theory at all. If you try it, please let me know how they performed for you next year.

  2. Sorry to hear about the leeks, its strangely reassuring to novices like myself that even the best don’t always succeed, (sorry!) Do you think low light intensities may also possibly be a trigger to bolting i.e. the plant thinks autumn is on its way? Did you add anything to the JI No 3 at final planting time and have you fed at all since final planting?

    Incidentally there was some very good stuff on the benches at NVS/Shrewsbury, particularly considering the weather and as a newcomer was made to feel extremely welcome by the guys and gals in the Midlands branch.

  3. I am going to go all altruistic and collect bulbils from this year’s prematurely bolted heads rather than buy new stock in as I usually do. That way I’ll have a definite answer to pass on to folk. My feeling is that going to seed prematurely cannot be a genetic thing, but down to physical conditions during the plant’s life cycle.

    Having said that, I may well be wasting a year’s leek growing!

    1. Simon, I have to say you are brave to sacrifice a whole years work for the sake of others, your unselfish concern for the needs and welfare of others is really remarkable! (I had to check the dictionary for the meaning of altruism or altruistic!!) To be serious though, I have every faith in Dr Dawson’s’ theory that they won’t bolt , good luck.


    1. All plants aim to achieve reproduction, therefore when a plant is under stress it re channels its energies from putting on growth to creating a seed head and this can happen at any point during its growth cycle. It necessary follows that bolting indicates the plant thought it was dying and in an effort to perpetuate itself it throws up a seed head. This can happen for various reasons such as what you said regarding being frosted, or they can be too wet or too dry or even pot bound for too long as I’m sure happened to me.

  5. Medwyn & Simon

    There is only one thing that will cause leeks to run to seed. VERNALISATION. A period of cold. If you ever get an onion or a leek showing a seed head, you need to look back over a month and think whether there were a few cold nights.

    I & others have been causing the Welsh Seedling to bolt for almost 20 years. Old leeks from last years shows always bring heads to early, so by growing some very early plants and exposing them to about a weeks cold around Xmas time usually results in heads a bit later and just about right and nice and fresh for striking in November.

    Another observation, the Pendle Improved Leek is more prone to bolting because of the odd cold night than the Welsh Seedling. Two years ago I grew 16 plants, they were in two rows of 8 on my greenhouse staging, the 8 nearest the glass bolted but none of the 8 in the next row bolted. They are very sensitive to cold.

    If you want to read some very interesting newish findings on the flowering concept. Put Florigen into a Google search. It seems all plants flower when the gene Flower Locus T produces the flowering stimulus in the leaves and then its moved to the meristem and causes reduction cell division. Some plants flowering is a response to short days, others to long days and many bi-annuals like leeks and onions to vernalisation through cold. Another thing I’ve noticed is the bigger they are the easier it is to get them to bolt. A young pip can have a cold period and not bolt but a bigger plant only needs a few cold nights and a month later up pops a seed head.
    Ivor Mace

  6. Wow, fantastic information for everyone. Have you tried zeatin to slow leaf growth and to thicken the basal plate, or GA to encourage leaf and delay flowering. These both affect flowering and the timing of, but I’m just messing with a few at the moment so cannot surely say … i think B12 also encourages leaf and delays flowering. The physical conditions you guys accurately describe before are 99.something percent true..but I suggest there’s a tiny bit more to it. If only there was a quick fix spray to make every plant flower reliably..maybe one day soon?
    Ps medwyn …I grew YOUR Cumbrian Pot leeks this year, I’m still a new guy to leeks but they were short , none bolted and as thick as my forearm. Local show winner and pride of my garden. Thanks.

    1. My apologies for the delay in replying to you, I have been up to my eyes trying to get our seed catalogue out. I have tried (GB) Gibberellic Acid many years ago when I was growing at the university of Bangor complex at Penyffridd. The theory seemed to be that you sprayed the dilution on young seedlings hoping to either increase the cells within the plant or elongate them. I was told by one of the Proffs. there that celery would be a good start so I sprayed some young seedlings with the dilution a couple of times.
      The thinking was that if we could elongate the cells the petioles or stalks would be longer and thicker. In the end there was no noticeable difference in any of the plants so I dropped the idea. Whether or not I had the wrong dilution or did I spray the plants at the wrong time. I’m not sure if you can purchase it anywhere and if you can is there any noticeable benefit from its use on any of the vegetables. I wonder if anyone else has tried these chemicals. I understand that some of the Giant Pumpkin growers have been using it and the way that the record in weight seems to be broken on a fairly regular basis might point out why its happening.

  7. Can I get a seed catalouge from you. As do not seem to see them any where
    Ashlings farm, magdalen laver,, ongar essex cm5 oex
    Thank you

    1. Our current catalogue will be on it’s way to you this coming week.

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