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For the first time ever I have grown onions from onion sets, they seemed to be doing really well, lush thick green “leaves” but suddenly I am getting what I can only describe as pointed caps to the top of some of the leaves.

What are these, should I pull them off and what does it mean for my onion crop? I have dug down around a couple of them and they are pretty much the size of giant spring onions currently so quite a bit of growing to do before they resemble proper onions? Any suggestions. It has been a very warm April, May and now June here in the UK I have been watering (about once a week) and putting feed down.

  • You wouldn’t happen to have a photo for us? – Stephie May 31 at 20:26
  • I will get one for you tomorrow when I get back up the allotment :) – Richard C May 31 at 20:38
  • It's possible that you have given them too much feed, and with the warm temperatures they are growing fast enough to complete their life cycle in one year not two. If they look like giant spring unions, they are not growing any bulbs that would survive the winter - except that you were going to eat them before that happens! – alephzero May 31 at 21:20
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Your onions are “bolting”, in other words, trying to flower and go to seed. The pointed tips are the flower buds. Flowering can be triggered by cold spells, drought, basically everything that stresses the plants, triggering the “go to seed to survive“ impulse. Or it can happen in sets that are so well supplied that they flower a year earlier than the usually biennial cycle.

If you are planting the onions for storage, you don’t want them to flower - it means they won’t grow further (at least not much) and they also don’t store too well. You can snap or cut off the flower stalks to stop the onions from putting even more energy into the flower, but it’s just somewhat mitigating the effect. If you are planning to use some “fresh”, e.g. in the spring onion state or similar, pick the bolting ones, leaving the non-flowering ones for storage.

If you are picking sets next year, don’t chose the big and fat ones, as they are more likely to bolt. About the size of a hazelnut, plump and firm is best. Sometimes you can get heat-treated sets, that were stored at temperatures between 25 and 30 C for up to three months, greatly reducing the chances of bolting. Picking the right cultivar also helps. And sufficient watering combined with a bit of protection in case of late cold spells also is a good idea if you planted early.

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  • That is frustrating there have been no cold spells at all this year, the onions where supplied by the allotment and where roughly the size of a hazelnut and plump and firm. Like I said I have been watering and the soil under the surface is still damp so confused as to what caused this, will take your advice and start lifting the ones that have bolted and hope that we get some that can be stored through the winter. Will try again next year :) – Richard C May 31 at 20:58

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