What to do in the garden in May

VEGETABLE GARDEN

  • Keep on earthing up potatoes, and promptly plant any still remaining. When potatoes have made about 15 cm of top growth, they should be earthed up, so that 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, meanwhile protecting the exposed tender growth from being caught by the frost. It will also kill any weeds that might have grown amongst the potatoes.
  • Harvest asparagus spears when they are no more than 18cm tall.
  • Thin out direct-sown vegetables such as spinach, carrot and lettuce seedlings, and water them well.
  • Regularly hoe of weeds, or they will take nutrients away from your plants.
  • Harden off outdoor tomatoes, courgettes and pumpkins for planting early next month.
  • Protect carrots from carrot flies by covering with horticultural fleece.
  • Weed around your onions and garlic to reduce competition for nutrients and water. Apply Ecoworm Soil Extract to boost growth.
  • Support runner beans with bamboo canes, and pea plants with twiggy sticks or pea netting. Runner beans and peas should be supported when they are still only several centimetres high, and long before they start to topple over.
  • Pinch out the growing points of broad beans as soon as the top cluster of flower buds has formed. This will reduce the risk of blackfly attack.
  • Sow half-hardy runner and French beans, sweet corn, marrows, courgettes and outdoor cucumbers.
  • Make further succession sowings of lettuces, carrots, salad onions and radishes.
  • Sow sweet corn. Plant sweet corn in blocks, not rows in order to get the best pollination.
  • Sow savoys and winter cabbages in nursery rows for planting out when large enough, in about one month’s time.
  • Sow main crop varieties of turnips (Golden Ball), carrots (Chantenay Red Cored and Autumn King) and beetroot (Cheltenham Mono). They will stay in the ground until autumn when they are lifted and stored.
  • Outdoors sow next winter’s staples, such as cauliflower, cabbage and Brussels sprouts, together with root crops, such as swedes, parsnips and turnips.
  • Plant out self-blanching celery seedlings towards the end of the month, close spaced in blocks to aid blanching.
  • Feed tomatoes with Ecoworm Soil Extract.
  • Harden off herb seedlings that were started off in March 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.

FRUIT GARDEN

  • Harvest rhubarb, picking only one-third of the total amount of stems.
  • Control weeds amongst fruit bushes (currants and gooseberries) and cane fruits (raspberries, loganberries, tayberries, blackberries etc.) and strawberries.
  • Keep a look out for apple sawfly, gooseberry sawfly, red spider mite, caterpillars and capsid bugs, the last three pests will attack most fruits. Spray only if they become a problem.
  • Watch out for slugs amongst strawberries.
  • Protect strawberries with straw (to control weeds and lift the berries off the ground) and netting (to keep birds off the fruit).
  • Protect the blossoms of summer fruiting strawberries from frost and continue removing the flower trusses from perpetuals (autumn fruiting) up until the end of May.
  • Remove gooseberry thinnings from the bushes of dessert varieties to increase the size of the retained berries on the bushes. Start by removing alternate berries in May and, if needed, thin again later on if those retained still appear to be crowded.
  • Thin established raspberry plants, as they produce many more canes than they need. Leave about six per plant. Remove weak, diseased or damaged canes first, and any suckers that have sprung up away from the parent plant. Support the canes by using two rows of parallel wires, inside which the canes can be loosely contained or tie weaker canes individually to wires if needed. Newly planted raspberries should be left to grow for the first season, and only the weakest canes removed.
  • Hang pheromone traps in plum trees from May to August to monitor plum-fruit-moth activity.
  • Hang pheromone traps in apple treesto reduce codling moth.
  • Remove blossom and fruits from newly planted fruit trees to help them establish properly during their first year.
  • Keep young fruit trees well-watered while they are putting on rapid growth.
  • Remove blossom and fruits from newly planted fruit trees to help them establish properly during their first year.
  • Plant outside melons sown earlier in spring towards the end of May. Choose a sheltered but sunny spot, or a cold frame. Provide them with a rich soil and plenty of water. Pinch out the growing tip after six leaves have formed.
  • Train grape vines. Grape vines will be producing shoots from the buds left after initial pruning. These will eventually need to be trained along wires spaced 40 cm apart or up a trellis, pergola or other support. Apply Ecoworm Soil Extract now and continued feeding throughout the growing season.

LAWNS

  • Feed your lawn with Ecoworm Soil Extract to encourage healthy green growth.
  • Water the grass during hot weather. Never allow lawns to dry out, especially newly seeded turfed lawns.
  • Continue sowing lawn seed and repairing bare patches in the first part of the month.
  • Lower mower blades to their regular summer-cut height. If you set too low and you will end up scalping the surface, exposing bare earth for weeds to germinate and if the cut is set too high coarse grasses will be encouraged.
  • Deal with moss and weeds.
  • Postpone mowing newly sown grass until it reaches 3 inches in height and make sure the mower blades are on a high setting.

TREES & SHRUBS

  • Feed trees and shrubs with Ecoworm Soil Extract.
  • Deadhead rhododendrons and azaleas as the individual flowers fade, so the they waste no energy in setting seeds. The bushes will look neater for it, as some varieties have a bad habit of refusing to shed their faded flowers.
  • Deadhead flowering camellias and pieris.
  • Remove suckers from roses.
  • Begin planting out tender shrubs such as fuchsias. Keep all newly planted shrubs well-watered if the weather is dry. Feed established plants with a Ecoworm Soil Extract if necessary.
  • Check quick-growing hedges such as thorn, privet and evergreen honeysuckle for excessive growth. Give them a light trim now, instead of delaying it, and having to prune drastically as a result. Regular trimming encourages compact, bushy growth, which is exactly what you want in a hedge. 
  • Keep on pruning any ornamental shrubs that have finished flowering so that they can produce more flowering shoots next year.
  • Keep an eye on roses for the appearance of greenfly, black spot, mildew and rust. It’s also a good idea to check roses now for any suckers that may have appeared round the base of the plant.
  • Clip hedges and begin training topiary plants.

FLOWER GARDEN

  • Harden off and plant out all the hardy and half-hardy bedding plants that you have been raising under glass. The actual time for planting will vary depending where you live but, as a basic guide, the second half of May is usually safe.
  • Clear spring bedding such as wallflowers and recycle them on the compost heap.
  • Lift tulips, hyacinths and other bulbs when the leaves have died down, dry off and save for replanting in autumn.
  • Plant window boxes, tubs and hanging baskets for placing them out in the garden. To provide instant colour so the plants must be well in bud or actually flowering when they are planted. Use a light compost for hanging baskets e.g. not one containing loam.
  • Plant out Dahlias and Early Flowering Chrysanthemums. The site should be thoroughly dug and well enriched with bulky organic matter. As both these plants need the support of a cane or stake, the latter should be pushed in the ground after the hole has been dug but before the plant has been settled in.
  • Divide hostas as they come into growth.
  • Trim back spreading plants such as aubrietaalyssum and candytuft after they’ve flowered, to encourage fresh new growth and more blooms.
  • Trim lavender plants, cutting off old flower heads and about 2.5 cm of the current year’s growth.
  • Water container plants.
  • Feed permanent pot plants with Ecoworm Soil Extract every 2 weeks.
  • Closely inspect plants for pests and diseases, because early prevention is much easier than curing an infestation.
  • Pick off any larvae of rosemary, viburnum and lily beetleas soon as you spot them.
  • Continue to weed beds and borders to prevent competition for water and nutrients.

Read more:
What to do in the Garden in April
What to do in the Garden in June