I got my patch last May and didn't put onions in until the middle of that month. They caught up fine and were one of my biggest successes last year - only surpassed by weeds and caterpillars

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What I'm saying is don't panic! I'll be digging a bed later this week for 100 sets. I'll also put more in the coming months.
BTW Poundland and Pound Stretcher both have different varieties of sets for £1. There's some decent bargains to be had in both stores. I have Stuttgarter, Red Baron and Snowball onions to go in along with Golden Gourmet shallots.
On a similar note, would now be an ideal time to plant Spring Onions seeds into grow bags?