Even if the days are warm, it can still be cold at night, so resist the temptation to sow or plant if the weather is bad. Protect outdoor sowings with fleece.
Here are some key allotment jobs for May.
Earth up potatoes
Potatoes planted up last month need to be earthed up this month. When the foliage is around 20cm tall, draw up the soil on both sides of the plants, creating a ridge about 15cm high that almost covers the foliage. This prevents the tubers turning green and protects the foliage from frost damage.
For help choosing the right spade see our Border spades buyers guide
You can start enjoying the fruits of your labours this month - crops that should be ready to harvest include lettuce, spring onions, broccoli, cabbage, spinach, rhubarb, beetroot, radish and peas. You can also start harvesting asparagus - cut the stems from 5cm below the soil.
Sow dwarf or climbing beans, runner beans, sweetcorn, indoor cucumber, courgettes, pumpkins and squash in the greenhouse or under cover. Continue to sow lettuce, radish, spinach and beetroot direct outside - little and often to keep the harvests coming - and parsnips. You can also sow cabbage, kale and purple sprouting broccoli, for transplanting next month. When sowing carrots, protect against carrot fly.
Thin out crops
Thin out crops sown last month, including beetroot and carrots. Be sure to cover carrots with fleece afterwards, as thinning out releases a carrot smell that attracts carrot fly.
Plant out young plants
Plant out young plants sown last month, including celeriac, courgettes, squashes, pumpkins and marrows and leeks. Hold off if the weather is cold, and protect young plants from cold or windy weather with a cloche or fleece.
For help choosing the right hand trowel see our Hand trowels buyers guide
Protect plants from bad weather
There may still be frosts in May, not to mention cold winds and rain. The nights in particular can be cold. Find out how to protect your young veg plants in spring.
Put up supports
Put up supports for climbing beans and runner beans. You can either buy a ready-made support, or make a wigwam or row using bamboo canes or hazel poles.
For help choosing plant supports see our guide to the Best decorative garden obelisk and plant supports for climbers
Carry on weeding
Weed, weed and then weed some more! Get on top of weeds now and you'll have less to do as the summer progresses.