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.

Potting Up Large Exhibition Onions


One important job that I have to carry out today is to pot up my large exhibition onions in order to get some good quality seed heads for next year. This year was an absolute disaster for me as regards growing the large exhibition onions, right from the day I planted them out, I just knew they would do no good.

What better way to get rid of the that bloated feeling after eating far too much turkey, plumb pudding and chocolates, than to get a little fresh air and some light exercise in the garden. One important job that I have to carry out today is to pot up my large exhibition onions in order to get some good quality seed heads for next year. This year was an absolute disaster for me as regards growing the large exhibition onions, right from the day I planted them out, I just knew they would do no good.


The problem was a combination of events that led up to it, the first major set back was when the joiner decide to turn up during mid February to start constructing my new parsnip bed cover. As the beds are only a path width away from my onion polytunnel, he used this as a workshop and I was unable to get back on to the soil until well into March. By this time my onions, which were in their normal 4 inch square pots, were really in need of either being planted in their beds or being potted up. The result was that I waited another week to try and prepare the ground before eventually planting them directly into the beds.


They grew well initially but a number of them bolted which was not unpredictable considering how pot bound they had become. However the good news was that I have some good growing friends out there who have my own strain of onion and a number of them very kindly gave me some of their own top quality bulbs to put down for seed. These were stored throughout the Autumn in my dry garage and the majority of them have kept really well.


The odd one or two have suffered from the sometimes inevitable Botrytis or grey mould which can totally destroy your bulbs. When I have such bulbs I don’t throw them away, they can still be used to grow your own seed. Remove the necessary layers of skin until there is no trace at all or any sign of the disease anywhere on the bulb. This can be a messy and often smelly job, but if you want to make maximum use of every onion that you have, then it”s worth doing it. After the onion has been skinned down, dry the bulb with a soft tissue in an attempt to remove any trace of the disease spores.

Removing the Outer Skin

The removal of some of the outer skin can be beneficial to the onion in the sense that any new roots that develop from the onion always appear from around the periphery of the root plate. Another good tip it to remove the top inch or so of the onions neck and shoulder so that when it starts to throw out some foliage it can do so unhindered. The onions need to be either planted up in soil in a greenhouse border or, as in my case in plastic pots using top quality peat based compost. In the past I have used Levington M3 very successfully but as I have a few Levington Gro Bags left over from last Summer I intend to use them this year.

Size of Plot

You must remember to give the plants a decent sized pot, not too large so that too much water can be retained in it with a risk of the onion roots rotting off. I generally use nine inch pots but this year I intend to use 4 litre deep pots which should give ample room for the roots to grow in. Do not push the bulb into the compost as this will merely firm up the compost underneath, simply clear away some compost to form a small nest and gently bed the onion in it.

Bottom Heat

I have discovered over the past couple of years that it is very advantageous if you leave the pots on some bottom heat. This can be either a heating blanket or on a sandy propagating bench which is the way I do it. The bottom heat seems to pull the roots down and before you know it they will start to emerge at the bottom of the pot. At this point remove them from the heat and place them on a bench within the heated greenhouse.

Transporting Pots

Moving pots with large heavy onions in them, at a point where they are starting to develop a strong root system, has to be done very carefully. The last thing you want is a jolt or a knock against the pot, this will inevitably dislodge the onion and will most certainly have snapped off some vital roots. Once they are on the bench, try not to move them about, just in case you disturb the roots, of course once the roots are well established you can easily then move them around.

Keeping a watchful eyes

Keep an eye on them and water judiciously, watch out for any grey mould or Botrytis that may appear on the skins and remove them as soon as you see any. I personally don’t feed the onions at this stage, but later on when they are out in the polytunnels, I will give them the odd feed of a balanced liquid fertiliser particularly when the seed head is developing. Once in full flower I change the feed to Phostrogen which has a slightly higher ratio of potash in it which will help towards the development of some large plump seed.

Leek Pips

My friend Steve Harris from the Rhondda valley in South Wales happens to have quite a few rooted leek pips of the Welsh seedling available. Steve used to be unbeatable on the show bench with his blanch leek until he packed in the growing to concentrate on building himself a new house a few years ago. However the good news is that he could be coming back with a vengeance in 2004, so watch this space. For further details contact Steve direct on 01443 771 023 or write to him at 1 Tylacoch Place, Treorci, Rhondda. CF42 6DH.


Growing Parsnips

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

Read More »
Leave a Reply

Your email address will not be published. Required fields are marked *