Any tips on preventing onions from bolting?

[Eyren]

I saw a post on here recently about onions grown from seed bolting if they get too warm, and I'd like to avoid that if possible! Thanks in advance for any advice - this is my first attempt at onions from seed (grown sets in the past) and I'm a bit nervous of getting it wrong!

My first lot were sown two weeks ago and have been on open shelving (no propagator lid) in my conservatory, which is south-facing, double-glazed and frost-free but only partially heated - there's a small radiator in the corner nearest the house, which is on during the day and evening, plus whatever warm air leaks in from the living room (we keep the inner door shut in cold weather to keep the heating bills down!).

My plan was to put them out as soon as they have germinated and are showing above the vermiculite, but if we have a mild spell it could get quite warm in the conservatory - would it be better to harden them off now and grow them in a fleece-covered mini-greenhouse on the patio?

[Paulottie]

Don't be panicking...Every chance of success. I would be setting out in about a months time. They tend to bolt for a couple of reasons. Irregular watering; lack of soil fertility(or too many weeds); shade/sowing too late...very light sensitive.

My top tip is to keep the soil surface fluffed up/hoed...I use one of those little hand rake thingamajigs (all the technical terms this morning!) They do like an open, fertile soil with no capping.

One other warning...from seed you maybe more likely to get onion fly problems. I used cloches in the early days last time but its a pain to keep taking them off and watering.

[Eyren]

Thanks for the tips - I'm hoping to get some municipal compost for the lottie, to lighten the soil a bit, and will add some general-purpose organic fertiliser in any case to give the soil a boost.

I'll bear the onion flies in mind as well. I'm going to be growing them alongside carrots, so I'll want to keep small flies off both crops - in theory they will mask one another's scent, but I'm not going to rely on it! Luckily I have a big enviromesh tunnel that I bought last year, which should do the job