Large Exhibition Onions - Pests, Mixture, Form
4th Feb 1998
Large Exhibition Onions
The large exhibition onion plants are now in 3" pots and really motoring away and very shortly they will have to be potted on into 5" square pots.
The potting mixture that I used at the 3" stage was the same mix exactly as last year and it really did produce some excellent quality plants. The mixture is the one that Mel Ednie used when he broke the World record for the heaviest onion a few years ago and is as follows: 3 parts potting compost, I use the Levington M2 at this initial stage, but I do know growers who have excellent results when using their own peat base mixture adding the Chempak potting base fertiliser as recommended on their packet.
The next element is 1 part sieved soil from my leek bed which was passed through a ˝" sieve in order to guarantee as rough a texture as possible, this roughness suits the onions as it allows free drainage and in so doing permits plenty of air to get at the root system. The reason for using soil from my leek bed rather then my onion one was because I had problems last year with white rot in the bed and even though all the soil in the three beds have been sterilised using Armillatox, I prefer to be cautious until I know that the beds are free from the dreaded disease.
The third part of the mixture is 1 part Vermiculite which is first moistened up a little to prevent it soaking up the water from the pots at a time when the very young seedlings are most vulnerable and trying to re establish themselves. The three elements are stored underneath the greenhouse staging for a few days prior to mixing so that the eventual compost will be close to the same temperature as they will be growing in minimising any risk of a check to their growing pattern. No added fertiliser is given at any of the potting stages and the plants seem to grow away well right through to planting out time with no supplementary liquid feeding being given either.
Don't be too hasty to pot into the next size pot, the roots need to be growing strongly and clearly visible through the bottom of the three inch pots. The mixture for the 5" pots is as follows: 4 parts of Levington M3 or again you can make your own mixture using Chempak potting base, 3 parts of the same soil as above and 1 part Vermiculite. At this point the plants will most definitely be better from being supported, and I have used plastic half round clips which clip on to split canes forming a complete circle for many years now. They are excellent for this work and come in tow sizes, small and medium. While they are growing you will need on occasions to re open one end of the clip as new growth will sometimes push itself outside the support area and the weight of the leaves in the end will prevent the plant from growing upright.
I have mentioned several times before how important it is to make sure from day one that the plants are growing perfectly erect and not allowed to flop around any old how. The best onion shape is only arrived at through thorough preparation care, keeping the plant bolt upright will ensure that your harvested onions will have perfect form. The word 'Form" used to be part of the judging criteria in the RHS Show Handbook but has now been replaced by the word 'Shape' because a lot of judges allegedly found it hard to understand what the term ‘Form" meant.
I have to say that though that ‘Form' as part of the meritorious attributes of onions was never a problem for me and simply means that if you look straight at an onion, imagine a vertical line passing through the centre of the onion's neck and down through the root plate. If you can further imagine the onion being revolved around this imaginary line, the mass of the onion should be evenly proportioned all the way around it. I have seen on many occasions good onions being staged that would have been even better had they taken more care during their growing season to ensure that the plants are kept bolt upright.
There is no doubt that two pests in particular can destroy the onions particularly now they are regularly grown under artificial lights and thereafter in polytunnels, situations that are perfect in very way for the Red Spider Mite and Thrips to thrive under. Regular spraying from now on using Polysect at double strength dose as recommended by the makers should help to make sure that these pests are kept under control.
If you want to have a go at staging collections or even the Garden News Top Tray, then parsley can come in very useful for garnishing around various vegetables, particularly Cauliflowers. Now is the time I like to have it sown to have plenty of strong plants to plant out in the Springtime. There are many varieties about with Faulds being a very old Scottish variety if you can get hold of some; another excellent type is Afro with long fronds that are tight and curly. Broadcast sow the seed in a small tray and pot the plants on into three inch pots when just showing their first true leaf using Levington M2 or a Multi purpose compost.