Early peas may be ready for harvest. Cut off the tops of the plants, leaving the roots in the ground to conserve valuable nutrients to the soil. Peas and other legumes can ‘fix’ nitrogen from the air.

Harvest salad onions, salad leaves, beetroot and radishes as they mature.

Harvest rhubarb stems until the end of the month, but leave crowns ‘forced’ earlier in the year to recover.

Continue with successional sowing of salad crops, beetroot, Chinese cabbage, pak choi and radish, to ensure an even supply over the season. In hot weather, leafy salad crops may do better when sown in partially shady sites. Hot dry weather can lead to bitter tasting leaves.

Overwintered Japanese onions can be harvested when the tops start to fall over. Leave the bulbs to dry in a sunny spot outside, or in a airy shed if rain is forecast. This will allow the skins to harden, and the bulbs to store better.

Early potatoes may begin to be ready for harvesting. Many are ready when the plants come into flower. Take care when digging them up to insert your fork some distance away and to lift the soil carefully. Otherwise you may pierce and damage the tubers.

If you have started off crops early under cover, and live in a mild part of the UK, you could be harvesting early crops of courgettes, small summer squashes, sweetcorn, calabrese, pak choi, kohl rabi, French and broad beans and carrots. Spring or early summer cabbages and cauliflowers planted last year will also be ready for cutting.

Continue to earth-up potatoes not ready for harvest (unless planted through black plastic). 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. Potatoes can also be grown in containers.

Plant out tomatoes if this has not already been done. Train them up canes or string, and remove sideshoots from cordon tomatoes. These sideshoots 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. Small sideshoots can easily be pulled off with a thumb and forefinger, and can be easily rooted to obtain more plants. When four flower trusses have formed, pinch out the growing point just above the highest truss.

Celeriac and self-blanching celery can be planted out this 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.

Outdoor ridge cucumbers can be planted out this month. They benefit from a site that has been enriched with lots of organic matter to help retain water. Pinch out the tip of the plant when it has made six pairs of leaves, to encourage sideshoot and cucumber formation. Feed regularly with a liquid tomato feed, following the instructions on the packet.

Sow French, broad and runner beans, peas, squash, sweetcorn, and outdoor cucumbers directly into prepared beds outside.
French beans are best sown in traditional rows, 45cm (18in) apart, at 15-22cm (6-9in) spacing.
Sweetcorn works best planted 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 slug damage. Any seeds sown earlier under cover can now be planted out into the same block pattern.
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.

Strings stretched along the sides of broad bean plants will support them and prevent them flopping once pods develop.

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

Courgettes, marrows and pumpkins can still be sown outdoors in early June. Encourage good fruit set by hand pollinating. Push the male flowers (distinguished by the lack of swollen stem/young fruit behind the petals) lightly into the female flowers.

Plant out other vegetables sown indoors earlier in the season, including winter brassicas and sweet peppers. Peppers can only be planted out when all risk of frost has passed. The gaps between winter brassica plants can be used for quick-maturing catch crops, perhaps radishes or gem lettuces, as brassicas take time to grow into their eventual spacing.

Although most winter brassicas need to be sown earlier in the season, you can still sow turnips now for an autumn crop, as they are best lifted while still young and sweet. Sow them in drills 15cm (6in) apart, and thin them as soon as they are large enough to handle, to leave one plant every 10cm (4in).

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).

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

Harvest spring lettuce, spring cabbage, salad onions and radishes. Continue with successional sowings of these and other salad crops. Herb crops such as basil, coriander and parsley can also be extended with successional sowings.

Asparagus is a perennial vegetable. Harvest spears from established plants for six to eight weeks from May into the early summer. Do not harvest spears from crowns less than two years old. After harvest and flowering, it is a good idea to feed them so that they have sufficient energy for next year’s crop.

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 creamy-black larvae. Pick them off stems and foliage by hand.

Look out for blossom end rot on tomatoes and peppers. This is not actually a disease, but the symptom of nutrient, calcium, deficiency that occurs when water supply is erratic. Regular watering and appropriate growing media should prevent too much damage.

Pinch out the top of broad beans once the lowest flowers have set. This will help prevent aphid attack.

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

Cover young brassica crops with nets to protect them from pigeons.

Keep carrot fly off carrots by covering them with a fine woven plastic mesh like Enviromesh. Just make sure that the corners are well 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.

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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