Elder Stubbs Charity allotments is a member of NSALG (National Society of Allotment and Leisure Gardeners) and their website gives a lot of useful information (www.nsalg.org.uk). This monthly task list is based predominantly from information from them.
Overview: As the soil is starting to warm it should be safe to sow seed directly in the soil. Pick a warm still day to do the job. Give the seed bed a final gentle raking to create a fine tilth. A good method can be to draw out the drills with a short stick because it allows better control of keeping a constant depth to avoid some seed being sown too deeply which could result in taking the germinating seedling longer to reach the surface or worse not being able to make it to the surface.
Sow: With favourable weather it is a good time to sow early beetroot, carrots, broad beans, kohlrabi, lettuce, parsnips, peas, radish, salsify, scorzonera, spinach, spring onions, turnips and whitloof chicory for forcing.
Some later cropping vegetables are better sown thinly in short rows on a separate seed nursery bed. They are later thinned to space them out and allowed to grow on before transplanting them to their final positions. These include broccoli, Brussels sprouts, cauliflower, calabrese, leeks.
Sow under protection in a greenhouse or cold frame: Outdoor tomatoes, pumpkins, squashes, courgettes, sweetcorn, outdoor ridge cucumbers, runner beans, dwarf and climbing French beans. Plant tomatoes, peppers, cucumbers and aubergine into their final position.
Plant: Complete the planting of onion sets and the second early and main crop potatoes. Transplant any early sown lettuce, cabbage, broccoli, celeriac, peas, broad beans, beetroot and spinach.
General: Set up the bean poles in preparation for transplanting the climbing French and runner beans. Be prepared to cover up any emerging shoots of potatoes if a frost is forecast. Organise peasticks or netting to support peas.
Harvest: Sprouting Broccoli, lettuce/salad leaves, leeks, spinach and cabbage.
Pests and Diseases: There may be aphids and whitefly under glass and the first signs of aphids appearing on the allotment especially in the more sheltered and warm areas of the site. A good indicator of aphids is an increase in ant activity climbing up affected plants.