Onion set preparation

A lot of people seemed to have decided in recent decades that large-scale onion production on allotments wasn’t cost effective. The last couple of years of recession have begun to change that view and lots more allotment-holders are getting ready to plant over-wintering onions than I’ve seen for a long time.

Growing overwintering onions is simple. It can involve either sets or seeds and this year we’re growing both. The sets are Electric and Senshyu and the seeds are Kelsae. This week we planted out the sets.

Soil for good onions needs to be rich in slow-release nutrients – if you use anything too juicy, like manure, too close to planting date, the onions just bolt, but if the soil is too poor, they don’t bulb up properly. As a result we use a granular slow feed about a week before planting them out. In previous years we’ve also used fish, blood and bone but that’s a bit of a non-starter on plot #103 as the local fox (lives in the shed next door) is very keen on vacuuming up that particular form of feed and will remove or tear through netting to get to it!

The soil also needs to be finely raked and for this we’re using raised beds this year. In previous years we’ve used a tiller to produce fine tilth in the open ground into which they can be planted.

Some people (and some ill-informed books) tell you to just ‘push’ your set into the soil. This is, in my opinion, a stupid thing to do. Onion sets are really easy to grow, but one of the very few ways you can make a mess of them is to start shoving them into the ground. Two things can happen that damage an onion: you can press too hard, pinch or twist it, so that the small bulb is bruised inside the papery skin which leads to a deformed onion or one that rots before it can grow, or you can push it down into the soil and come across a pebble, stone or other hard object, which tears a hole through the root base of the set and leads to rot or deformation as above.

Instead of pushing, try dibbing little holes for your onion sets so that they can be popped, rather than pushed, into the fine soil. The pointy end goes up, the nubbly or whiskery end goes down (never be embarrassed not to know stuff like that – everybody has to start somewhere!) Plant on a dry day, preferably with a couple of days of dry weather beforehand – that’s why we get ours in the ground in October, because November is too unpredictable in terms of rain. Gently nudge the soil back around the set.

We plant ours around 15cm apart. If you put them closer together you get smaller onions, but if you set them further apart, you don’t get bigger ones, unless you are growing something in the exhibition line, like Kelsae (which I’ll be posting about in a couple of weeks). It’s also good to note that if you find some of your sets are tiny, they are actually the better plants, as they are less likely to bolt – the bigger the bulb the great the risk of it bolting and producing a flower-head.

Once they are planted, cover the planting area with netting to stop birds pulling them out of the ground and then lift it whenever you need to, to hoe or hand-weed between the sets. You don’t need to water, overwintering onions are more likely to rot through overwatering than to dehydrate through lack of it.


And that’s it! Once the sets are well rooted, you can take the netting off permanently, and then leave them, apart from weeding/hoeing, until you lift them in June.

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Posted by The Allotment Blogger on Friday, October 14, 2011

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