I have just taken the decision to scrap ALL of my March 3rd sowings due to an across-the-board 90%+ failure of onions, spinach, tomato, beetroot, cabbage and lettuce. The big seeds of broad beans and peas did OK-ish. I used seed from a range of suppliers (Seed Co-op, RSC, Kings, etc.) In this instance the compost is to blame! Westland Black’s Magic bought from the local nursery, who guarantee me that it was new stock, proved overly strong as evidenced by the visible cotyledon scorching on some of the survivors. My fault for straying from organic, hopefully have enough home-made stuff for next year.