May is the ideal time to sow some delicious veggies. The RHS site says:
Sow French beans, runner beans, squash, cucumbers and pumpkin seeds directly into prepared beds outside. Be alert to late frosts (for which a covering of horticultural fleece should provide sufficient protection).
Sow sweet corn outside in blocks, at least 45cm (18in) spacing, with two seeds per hole. The strongest seedling can be selected later.
Sow cauliflowers and purple sprouting broccoli for harvesting next winter.