If you happen to have had a particularly good onion and you want to save it for seed do remember that if you plant it now in a pot, it will need room to grow and it certainly means growing it indoors. After the risk of frost the heads can be moved outside for a while but they must be brought indoors again before the flowers start to open up.
This year I had some marvellous seed heads off the large exhibition onions that I re planted for seed production towards the end of December last year. The resulting seed from these heads, although excellent in every sense, they were somewhat late in ripening and it was early October before I could take the heads off. This year I intend to speed things up a bit and plant the onions this coming weekend. If you happen to have had a particularly good onion and you want to save it for seed do remember that if you plant it now in a pot, it will need room to grow and it certainly means growing it indoors. When the heads are fully developed the plant needs considerable space as they can easily be over 4 feet in height and each head will need a cane to support it
Avoiding cross pollination
After the risk of frost the heads can be moved outside for a while but they must be brought indoors again before the flowers start to open up. This will ensure that should there be another onion gone to seed in close distance to your garden, cross pollination could take place which could result in some rogue seeds the following season. If you think you are going to have some spare space in a greenhouse which has a border of soil, then the easiest way would be to plant the onions direct into that soil which would give the emerging root system an unhindered root run.
Last year I only saved two of my best onions and they were planted just as they were, no outer skins were removed and even though one onion that I had from Mel Ednie was over 27 inches around it never went rotten on me and produced two marvellous seed heads. If you are suspicious that your onions will rot on you before they seed, then you can remove some of the outer layers of flesh, because after all these are mainly made up of water and at a later stage I would remove them anyway before they rotted away.
I thoroughly check each onion before planting them to makes sure that the area around the root plate is solid and healthy as well as the area around shoulder of the onion. Gentle pressure with you thumb around the shoulder will usually give you an indication of it’s condition. If the onion is soft then the probability is that it will rot before producing any leaves. The best onions will probably have been at flower shows and once they were brought back home, the raffia would be removed and a thin pointed split cane would very carefully be pushed into the neck to open up the dried layers of tissue that have been squeezed together to form the thin neck. This will have allowed the onion to breath and inevitably they will keep better as well.
Prior to planting remove this shrivelled neck so that when the emerging shoots develop they won”t have any problems in pushing themselves out of the onion.
Every onion is planted up into nine or ten inch pots and I have actually used florist buckets which you can usually pick up cheap from a large florist shop. Drainage holes will have to be inserted into them and I drill six holes with a 10mm bit spaced evenly around the perimeter. The onions that I select will have a rounded base, I prefer not seed from flat bottomed onions as I feel that this will produce even flatter onions which don’t really catch the judges eye in the same way.
The pots are filled up with fresh compost, I use Levington M3, this has some slow release nutrients which will sustain the plant growth right through to seed harvesting time. Plant the bulb on top of the compost and water it in, after this point it”s important to place the pot in a position inside your greenhouse where it won’t be moved. Any movement at all once the new roots are emerging could snap them off, hence the need to really think through where the onions are going to be grown so that you won’t have to move them around all the time.
As I had a number of well shaped deep bulbs this year I intend to plant them all so these will be taken to the University College commercial cold greenhouse at Bangor where they will have ample room for development.