There's a lot of folklore around sowing onion seeds, the most popular one being that the biggest bulbs are grown from those sown on Boxing Day - or even Christmas Day.
Of course, there's a lot of truth in this, especially if you want onions for the exhibition bench in September - they need all that time to grow so big!
However, you can still use this method for alliums that will end up in your kitchen - it's a nice little job away from the festivities.
Bear in mind, though, this is for onions from seed only - sets are started off in spring.
If you really want to put your feet up, you can sow right through to February - but expect smaller bulbs.
For best results, choose varieties such as Wellington, Red Sunrise, Kelsae, Robinson's Mammoth, Rose de Roscoff, Bedfordshire Champion or Red Pearl.
To sow, fill a seed tray or cell insert with good-quality seed compost and tamp down the surface, then water in (doing so now means you won't disturb the spacing of the seeds) .
With cell trays, sow four or five per compartment, sow thinly in a standard tray, then lightly cover with 5mm (¼”) more compost.
Cover the tray with a propagator lid, or sheet of glass/polythene. The ideal germination temperature is 15-20°C (60-68°F), but it should not be lower than 15°C (60°F).
After germination, remove the cover and move to an area with plenty of light. Keep the compost damp. Maintain a temperature of about 18°C (65°F) until "crook stage" (when the seedling is still looped over like a shepherd’s crook, with the tip of the seed leaf still in the compost, usually two-three weeks after germination, just before the second leaf).
After this, place them somewhere cooler, reducing the temperature to 10°–13°C (50-55°F). The seedlings need maximum light and ventilation until the pricking out stage but be careful of scorching from direct sunlight. Transfer boxes and trays to a cold frame in March or April.
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