If you’re growing your own onions, one of the biggest hurdles is a problem called bolting when plants send up a flower stalk instead of forming a proper bulb. It’s usually caused by earlier exposure to cold, which tricks the onion into thinking it has already been through winter. Once an onion decides to flower, you’re left with smaller, poorer-quality bulbs.

That’s why our Heat Prepared Bolt Resistant Onion Collection is so popular with both allotment and home growers. Each set has been carefully heat-treated for up to 20 weeks in a temperature-controlled store, where temperatures reach 30–32°C. This process kills the dormant flower embryo within the set, meaning it is far less likely to bolt to seed. Instead of diverting energy into producing a flower, the plant focuses fully on strong bulb development resulting in larger, firmer, usable onions.

Heat preparation also reduces the risk of bolting during periods of drought or extreme weather, when the plant’s natural “fight or flight” response can trigger seed production to secure a future crop. While nature can never be completely controlled and the occasional bulb may still set seed, heat-treated sets dramatically reduce the risk, giving you far more reliable, high-quality harvests.