Continue hoeing to prevent weeds from becoming established. Keep an eye open for pests and diseases and treat them appropriately as soon as they are seen so they don't have a chance to build up. The most common problem will be greenfly in May, while some early caterpillars may also be about.
From May onwards new vegetables will start to mature ready for harvesting. These include spring cabbages, spring onions that were sown last August, plus lettuces and radishes.
Thin vegetable seedlings sown last month, such as carrots, turnips, onions and leeks. To minimise disturbance, you can simply cut the unwanted seedlings off at ground level, rather than pull them up. After thinning, water thoroughly to settle the remaining seedlings in and get them growing again. Never leave the thinning lying on the ground nearby but remove them from the site. Particularly for carrots, as wilting plants can giving off a strong scent that attracts the damaging carrot fly.
Now is the time to provide support for growing peas as well use traditional twiggy pea sticks or erect a temporary support made from netting held in place by posts at each end of the row. Give the netting additional strength by inserting bamboo canes through it at regular intervals, pushed well into the ground.
The main crops to be sown in the open this month are the half-hardy runner and French beans, sweet corn, marrows, courgettes and outdoor cucumbers. These vegetables will clearly ripen later than plants raised under glass, or garden cloches, but they will still have ample time to produce full crops. Always be ready, though, to protect them from frost, once they are growing.
If you run short of cloches you can improvise with plastic bottles and upturned jam jars, placed over tender seedlings, in order to give them a head start. Jam jars (shown left) are ideal for small seedling such as dwarf french beans as they keep the moisture in and the frost out. Any clear plastic packaging lids from vegetable or egg boxes can also be used, but will need weighting down with a few stones, to stop them from blowing away.
Pigeons, cats, dogs and small rodents can become a nuisance in the seed beds at this time of year. Use cotton strings, fleece or netting to cover the area to prevent damage.
Harden off half-hardy plants such as aubergines, peppers and tomatoes. In mild areas, they can go out at the end of the month, otherwise wait until early June. They can be planted outside where they are to mature. Don't forget to pinch out the growing points of the first two, at about 15cm (6 in), to get bushy plants.
Plant outdoor tomatoes 45 cm (18 in) apart with 60 cm (24 in) between rows. Plant marrows and courgettes 60 cm (2 ft) apart, sweet corn 45 cm (18 in) apart and 60 cm (24 in) between rows.
Tomatoes will also need feeding. There are special proprietary liquid fertilizers available-and the unwanted shoots forming where the leaf stalks meet the main stem should be pinched out.
Many of the brassica seedlings that have been raised in the open, from seed sown in March and early April, will now be ready for planting in their final positions
Peas and runner beans should be supported when they are still only several centimetres high, and long before they start to topple over. Peas are best dealt with using either twiggy sticks or purpose-made pea or bean netting. Runner beans can be supported with the same netting but canes are normally used. If the beans are in a double row with 60 cm (2 ft) between the rows, bend the canes towards each other and tie the tops together. Then to make the support even stronger, fix more canes along the apex. An alternative system involves growing the beans in a circle and supporting with a wigwam of canes, which can look very decorative.
As soon as the top cluster of flower buds has formed, pinch out the growing tips of broad beans. This helps keep down blackfly, which are particularly partial to the succulent shoots.
When potatoes have made about 15 cm (6 in) of top growth, they should be earthed up, so no young tubers are exposed to the light, or they will become green and inedible. This will also encourage the formation of many more tubers from the underground section of stem and, at the same time, protect the exposed tender growth from being caught by the frost. It will also kill any weeds that might have grown amongst the potatoes.
Herb seedlings that were started off in March can be hardened off and planted outside. Dill, parsley can still be sown indoors and basil and sweet marjoram can be sown outdoors in May. Cuttings can also be taken of sage, thyme and marjoram.
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Continue to harvest and enjoy asparagus.
Early sown lettuces should be ready for picking.