We usually hear 'it's too late to grow anything' in May in Ireland! But there are so many vegetable seeds that you can still sow, and some plants are best sown in May or June! Given the exceptionally chilly spring we have had this year, even if you missed April sowing, plants sown in May should quickly catch up with them.
Carrots - late May or early June is the best time to sow carrots to avoid carrot root fly, but you can also do later sowings as well.
Cucumber - Cucumbers love heat and will absolutely refuse to germinate in a cold Irish early spring. Sow them too early indoors and they grow more quickly than the time it takes for Irish summer to show up! By sowing them in May they'll get a head start and can be planted out in June (under cover if possible).
Courgette - Same as cucumbers!
Peas - the ground is now warm enough to direct sow peas - there's nothing like snapping off fresh pods for your dinner!
Borlotti Bean - you can sow Borlotti bean from now until mid summer! The beautiful patterned beans are insta-worthy!
French Bean - another heat lover which is best sown in May/June. Grow under cover (polytunnel, greenhouse, conservatory)
Spring Onions - can be sown in May and June to give a continuous supply, they mature so quickly you'll be eating them in no time!
Beetroot - can be sown directly outdoors in May, or in modules and transplanted outside. In fact you can sow beetroot up to July for a succession of plants. It's great for filling in empty spots around the garden!
Salads - Salads tend to bolt in full hot summer sun, so sow in partial shade at this time of year. Can be sown all the way to August and you can even grow some salads over winter
Tomatoes - yes tomatoes! While you can sow tomatoes as early as February indoors for an earlier harvest, tomato plants in Ireland can produce as late as November most years. Sowing in May still gives plenty of time for them to grow and produce fruit, especially if you give them additional protection from the cold if temperatures dip. You can also harvest any remaining green tomatoes at the end of the season and ripen these in a bag indoors, or make green tomato chutney!
June is pushing it to sow tomatoes but if you have them in a polytunnel or greenhouse you will still get a harvest which is better than no harvest - even better if you can give them heat or move them indoors when the temps really start to drop in late autumn!