Spring isnt the only time for planting onions ,you can plant Japanese overwintering Onions and the best tasting Shallots in the Autumn.

“It’s hard to imagine civilization without onions.”
-Julia Child

The varieties I would recommend for taste and yield                                                             Onions                                                                                                                                            Silver Moon  Senshyu   Red Barron

Shallots                                                                                                                                           Jermor     Brittany long   Eschalot Grise

A dressing of calcified seaweed at planting helps with PH as onions prefer a PH around 6.5 Autumn planting is not suitable for heavy soils prone to waterlogging as the crop is more likely to succumb to disease

Over-wintered onions and shallots greatly benefit from an application of 35g per sq m (1oz per sq yd) of nitrogen-rich fertiliser such as sulphate of ammonia in late Febuary/March. This not only enhances growth but can also help suppress premature flowering. Alternatively, use dry poultry manure pellets