Harvest spring lettuce, spring cabbage, salad onions, salad leaves, beetroot and radishes as they mature. You can continue with successional sowing of salad crops, to ensure an even supply over the season.

Sow French and runner beans, squash, cucumbers and pumpkin seeds directly into prepared beds outside - in colder regions you should wait until the end of the month. Be alert to late frosts (for which a covering of horticultural fleece should provide sufficient protection). French beans are best sown in traditional rows at 15-22cm (6-9in) spacing.

Sweetcorn works best sown in blocks, at 45cm (18in) spacing, with two seeds per hole. The strongest seedling can be selected later, and you will have the safety of knowing there is a fall-back in case of one seedling being devoured by slugs (link to advice) or similar.

Runner beans benefit from well-prepared ground with lots of well-rotted manure and organic matter dug in. They need to be planted alongside suitable supports (often a frame or wigwam of bamboo canes tied together with twine) for the shoots to twine around and grow upwards.

Sow cauliflowers and purple sprouting broccoli for harvesting next winter.

Try sowing some unusual vegetables such as kohl rabi (like a large white above-ground turnip), scorzonera and salsify (both of which produce edible roots, which are boiled and peeled like parsnip and have been said to taste a bit like oysters).

Brussels sprouts for next winter should now be ready for transplanting after early or mid-spring sowing. The gaps between them can be used for short-term ‘catch-crops’ like radishes or gem lettuces, as they will take time to grow into their recommended spacing requirement.

Plant out artichokes that were previously sown under cover. They are tall handsome plants, and the steamed unopened flower buds are considered a delicacy. They can be grown as perennials (in which case they need 90cm spacing), or as biennials (45cm spacing is sufficient).

After all risk of frost has passed, plant out tomatoes, courgettes and pumpkins that were previously sown under cover.

Self-blanching celery can also be planted out towards the end of the month. A well-prepared site with lots of organic matter dug in is essential. Planting celery in blocks aids the blanching process, as does placing a strip of plastic around the edge of the block to exclude some light and further improve the pale colour and sweetness of the blanched stems.

It is still possible to sow vegetables indoors, especially in colder regions. This will shorten the growing time needed to reach maturity and harvest. Young plants can be planted out once conditions are suitable.

Ridge cucumbers can be sown indoors now, for planting out in early June. Two seeds per pot work well, then selecting the most vigorous seedling from each pot for growing on and planting out.

Earth up potatoes (unless planted through black plastic) when the shoots are 23cm (9in) high, in order to prevent the new tubers going green. Earthing-up is the drawing up of soil around the stems of the plants, leaving just 5cm (2in) of shoot uncovered so that the plant has enough foliage to continue growing. You can also grow potatoes in containers.

Leeks can either be sown in rows outside in a traditional seedbed, or indoors (earlier) in modular trays, with five or six seeds per module. Either way, they need transplanting when they reach about 10cm (4in) in height. A large dibber (or old spade handle) is used to make holes (about 7cm deep) for individual plants in their final positions. Drop each leek into a hole, and then fill the holes with water. For module-grown leeks, each cluster is transplanted as one unit, the hole then being filled with water in the same way.

Witloof chicory can be sown this month, to have some ready for forcing next winter (when other salads can be scarce). Sow in drills directly outside.

Start to remove sideshoots from cordon tomatoes that were started off early under cover. The side shoots develop in the leaf axils (i.e. between the stem and leaf), and if allowed to develop will sap the energy of the plant and reduce the quality of the yield. Sideshoots can be pulled off with a thumb and forefinger. It is now too late to sow new tomatoes, as they will not have time to ripen over our British summer.

Thin out sowings of Florence fennel made last month. The final spacing should be 20cm (8in), with 45cm (1.5ft) between each row.

Strings stretched along the tops of broad bean plants can support them, and prevent them ‘flopping’ once pods develop.

Peas need staking with pea sticks, netting, or pruned twigs from the garden.

Control weeds to prevent them competing for moisture and nutrients. Hoe regularly between rows on hot days to make sure the weeds dry up and die without re-rooting. Weedkiller is usually inappropriate as there is a high risk of it killing or damaging your crops as well as killing the weeds.

Pest & disease watch

Keep an eye out for asparagus beetles, which are black, red and yellow, and their cremy black larvae. Pick them off by hand.

Watch for the small holes flea beetles make on brassica seedlings. Water plants well to help them continue growing despite the pest damage.

Pinch out the tips of broad beans once they start to flower. This helps to discourage blackfly, which otherwise can decimate tender new growth.

Pests can be kept off a wide range of crops, carrot fly on carrots being a good example, by covering them with a fine woven plastic mesh like Enviromesh. Just make sure that the corners are tucked in or buried to prevent them breaching this defence.

Ensure that crops remaining in the ground, new sowings under cloches, and any stored vegetables, are well protected from mice.

Slugs pose a threat, and slug controls are necessary now, as always.

Pigeons are serious pests of brassicas and other vegetables. Cloches, frames of netting or fleece, and metal cages will help to keep them away from vulnerable crops.

Pick yellowing leaves off brassicas promptly, to prevent spread of grey mould and brassica downy mildew. Do not compost such material, but put it in the rubbish, burn it, or bury it deeper than 60cm (24in) depth.

Damping off of seedlings can be a problem with sowings both outside and in modules or containers. Clean equipment and, where necessary, use of fungicides (e.g. Bio Cheshunt Compound) can help to control this problem

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