Last Updated on March 20, 2023 by the Dobies Horticultural TeamTraditionally exhibition onions are sown on Boxing Day so if you are brave enough to have a go then you need to be ordering your seed now. Onions are one of the most difficult vegetables to grow which is why so many people covert the prize for the biggest and best specimens at their local shows. But it’s not all about winning. Why not simply give it a go, you’ll be wanting to grow onions to eat anyway.
The variety that Dobies recommends is aptly named ‘Exhibition’. Not only will this seed grow into huge 100g onions the flavour will still be excellent and, unlike other monster onions, they will store well.
If aiming at national shows then you will need to invest in a heated bench, fluorescent lamps, reflectors, ventilation fans and poly tunnels. If however your ambitions are more modest and you just want to win at a village show then you won’t need so much equipment, the advice that follows is aimed at helping you, not the big boys.
Using a good seed compost sow your exhibition onion seed in a heated propagator, lightly covering with sieved compost. Once the seedlings have germinated place a fluorescent light above them as this will stop them growing leggy and build a “wall” of tinfoil around them to reflect the light.
Once the seedlings begin to straighten out of their crooked stage pot them on individually into 3” pots. Once the roots have filled the pots move them on into 1.5 litre pots and support the leaves using short canes and clips. You want them to grow strong and straight. The next stage will be to move the plants into 3 litre pots and there they can remain until ready for planting out.
Water your exhibition onions from the bottom as watering from above may cause the bulb to rot. And don’t worry about feeding at this stage, provided you’ve used good quality compost the plants will be fine.
Once the risk of frost has passed then the onions can be planted out, ideally in a poly tunnel or raised bed. Depending on how serious you are about winning the prize you may wish to select about 6 of the strongest plants and put them into their own 20 litre pots, again giving the leaves some support.
We’ll be returning to your exhibition onions in future blogs giving advice as to how to encourage the formation of monster bulbs. There seems little point giving you June advice in December!
And if you are too full of food on Boxing Day to start your onion seeds then don’t worry. A delay of a few days will make no real difference.