Essential tasks for May
Keep your garden looking its best with our guide to essential tasks that need doing in May.
In the Flower garden
Hardy annuals: Finish sowing hardy annual flowers outside in May. Later sowings will result in later blooms.
Feeding: Sprinkle general purpose fertiliser around clumps of spring-flowering bulbs. Ensure permanent shrubs and hedging are given a generous feed using this or rose fertiliser. Hoe it into the soil's surface and water in before covering with a mulch of garden compost.
Support plants: Place support frames over tall perennials, or those with a floppy habit. Remember to put eye guards on top of any canes used.
Hellebores: Prune back the flowering stems of hellebores, such as Helleborus argutifolius, as soon as blooms are past their best. Cut back to their base to make room for new shoots. If seedlings are required, leave a stem to set seed, then collect and sow it when ripe.
Tidy alpine plants: Lightly trim off dead flowers of moss phlox, saxifrage, aubrieta and other alpines once they have faded. Excessive growth should also be trimmed to keep plants tidy. Rooted portions can be potted up separately.
Penstemons: Now that the danger of frost has passed, cut down last year's growth from perennials such as penstemons. This will encourage new flowers to bloom during the later summer months.
Chrysanthemums: Plant out young chrysanthemums raised from cuttings in early May, planting each one next to a tall cane.
In the Glasshouse
Seed sowing: Continue sowing seeds of summer bedding plants. Thin out those in trays, or prick them out individually into pots.
Hanging baskets: Plant up baskets with fuchsias and tender perennials, then hang them in the greenhouse to develop. Use our step-by-step guide to planting a hanging basket.
Plant care: In May some plants, such as fuchsias, benefit from pinching, removing the very tip of a shoot to encourage branching. Check plants regularly as their demand for water increases, most will also benefit from weekly liquid feeds. If plants are becoming pot-bound, move into bigger containers.
Pest control: Watch out for pests. Treat immediately with conventional pesticides, or consider using biological control agents for the control of whitefly, red spider mite and other pests. Most biological controls are very sensitive to pesticides, so do not use any sprays on plants if you are considering using them.
In the Kitchen Garden
Outdoor sowings: Crops to sow outside or under cloches during early May include dwarf French beans, beetroot, sprouting broccoli, Brussels sprouts, summer and savoy cabbage, cauliflower, ridge cucumbers, endive, kale, kohl rabi, lettuce, marrows, peas, radish, spinach, swede, sweet corn and turnips. Delay sowings if soil conditions are cold and wet.
Peas and Beans: For an early crop of beans, sow French and runner beans in pots in the greenhouse or on a windowsill. Choose deep pots, if possible, sowing two seeds per pot, and thinning to leave the strongest seedling which is then planted outside in late May or June. Alternatively, sow directly outside under cloches in May or June for a slightly later crop. For broad beans pull the soil up around the base of the stems with a hoe for extra support. Remember to support peas by pushing twiggy supports into the soil along rows of tall peas to provide support as they grow.
Rhubarb: Harvest stems forced under jars, by gripping them firmly at the base and then pulling them sharply away from the crown.
Water new plants: Water newly planted fruit trees, roses and shrubs regularly to help their root systems establish.
Plants for pots: Buy young plants for pots and containers as well for bedding displays. Most need to be potted up into 7.5cm (3in) pots and grown on in warm, bright conditions ready for planting out at the end of May. Be sure to acclimatise plants to cooler outdoor conditions before planting out.
Frost protection: Don't be lulled into a false sense of security by warmer days. While the weather continues to be unpredictable, it pays to take precautions. Keep a sheet of fleece handy, ready to use on cold nights if a ground frost is forecast. Throw it over emerging potato foliage, or fruit trees and bushes in flower. Sacking or sheets of bubble polythene can be spread over cold frames and newspaper spread over young plants on greenhouse staging at night will add a little protection.
Plug plants: Seedlings and plug plant packages that you have delivered during April and May should always be opened immediately, as any delay can be detrimental to the plants, causing leaves to yellow and rot to set in. Make arrangements for a friend to collect and open any that arrive while you are away.
Slugs and snails: Control slugs and snails by trapping them under tiles or grapefruit skins. Collect the slugs and dispose of them. Only use pellets sparingly.
Vine weevil: Where vine weevils have been troublesome pests, perhaps in pots in the greenhouse, consider drenching compost with a biological control nematode that will kill the grubs. Mixed into a solution and watered around susceptible plants, the nematode travels through soil moisture on its search for weevil grubs. The nematode is not active when temperatures are below 12˚C (55˚F), so apply when conditions are warm.
Aquatic plants: Plant up new aquatic baskets with water lilies and other pond plants. If you have large, overcrowded plants, now is a good time to divide them.