[MyAchingBack]

I want to try and grow Showmaster onions on the allotment next year. Looking through the internet the general advice is to keep the onions warm and well watered. Can I grow them in a garden tunnel with plastic covers or will this be too hot?

[Trillium]

Warm and watered is usually the germination advice for onions. If you're growing them for show, then uncovered in a tunnel can keep them more pristine and protected. But if growing them for eating, yes, the tunnels can get too hot for them unless you're on frequent temperature alert. They're part of the allium (garlic) family which prefer cooler temps.

To get nice sized ones, start them early, like Dec or January in modules so their roots can size up and by the time they go into the ground, they'll already be a decent size.

[devonbarmygardener]

I generally start my onions off in halved toilet rolls.

Once they get a flash of green shoot and a good root ball I put them in.

A fleece tunnel helps keep temps stable for overwintering onions, otherwise I just mesh them for protection from onion fly.

Hope this is helpful.