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Gardening in Italy?→ May’s almanac for the Italian climate
ALMANAC · UK CLIMATE

The garden in May

May is the month the garden fills out. Late frosts become rare by the second half of the month in most of the UK, so bedding, tomatoes, dahlias and patio plants finally go outside.

Growth is fast now, and so are weeds and pests. A little attention every few days — tying in, hoeing, checking for aphids and lily beetles — saves hours later in the summer.

UK and similar cool temperate climates. In northern and upland gardens wait until the end of May or early June to plant out tender plants.

AT A GLANCE

Spotlight: planting summer containers that last

Containers that look good in May and tired in July have usually run out of water or food, not luck. Start with the biggest pot you can manage: more compost means a larger reserve of both, and fewer daily emergencies.

Use a good peat-free multipurpose compost with some added grit for drainage, mix in a slow-release fertiliser, and plant closely so the display fills out quickly. Match plants to the light: busy lizzies, fuchsias and begonias for shade; pelargoniums, lantana, mandevilla and zinnias for sun. A climber such as mandevilla needs a small trellis or obelisk from the start.

Water thoroughly after planting and whenever the top few centimetres are dry — in hot weather that can mean daily. From midsummer add a high-potash liquid feed every week or two, because slow-release granules are usually exhausted by then. Deadhead regularly, and pinch back straggly stems in July to get a second flush that carries the display to the first frosts.

Busy lizziePelargoniumLantanaMandevillaZinnia Watering plants in pots ›

Jobs this month

Planting out

Once nights stay mild, tender plants can go out. Water them in well and keep an eye on them for the first week — cold winds scorch leaves even without frost.

Plant out bedding: busy lizzies in shade, snapdragons and zinnias in sun. Planting out (hardening off) › Busy lizzieSnapdragonZinnia
Plant dahlias, cannas and coloured callas outdoors late in the month. DahliaArum lily
Plant tomatoes, peppers and cucumbers in the greenhouse; outdoor ones at the end of the month. TomatoChilli pepperCucumber
Move bougainvillea, oleander, lantana and plumbago outdoors to their sunniest spot. Moving plants indoors/outdoors seasonally › BougainvilleaOleanderLantanaPlumbago

Borders and shrubs

Perennials grow fastest in May. Supports put in now are hidden by foliage later; supports put in after a storm never look right.

Stake delphiniums, peonies and tall leucanthemums. Staking & supporting plants › DelphiniumPeonyShasta daisy
Clip pittosporum and bay hedges and topiary for the first time. Trimming a hedge › PittosporumBay
Deadhead pieris and rhododendrons after flowering. Deadheading › PierisRhododendron
Let bulb foliage die down naturally before cutting it. DaffodilTulip

Kitchen garden

Tender crops can be sown and planted outside; successional sowings keep salads coming.

Sow runner and French beans, courgettes and squash outdoors late in the month. Propagation: sowing seed › French beanCourgette
Sow lettuce and beetroot every two to three weeks. Propagation: sowing seed › LettuceChard
Thin carrot seedlings in the evening and cover with mesh. Carrot
Earth up potatoes and cover them if frost threatens. Tomato

Pest patrol

Pests multiply quickly in warm weather. Most are controlled by predators if you give them a week or two; check before you spray anything.

Rub out aphid colonies on roses and shoot tips, or let ladybirds and blue tits deal with them. Rose
Go out with a torch on damp evenings to collect slugs from vulnerable plants. Keeping slugs off vulnerable plants ›
Check lilies daily for lily beetle and larvae. Lily

Sow and plant

Sow
  • Runner and French beans, courgettes, squash (outdoors, late May)
  • Lettuce, beetroot, carrots, chard (successional)
  • Biennials: foxgloves, wallflowers
  • Herbs: basil under cover, coriander outdoors
Plant out
  • Summer bedding and patio plants
  • Dahlias, cannas and callas
  • Tomatoes, peppers, cucumbers
  • Hanging baskets

Watch out for

AphidsGreenfly and blackfly on soft growth; most colonies collapse once predators arrive.Slugs and snailsNewly planted bedding and vegetables are most at risk.Box tree mothWebbing and caterpillars inside box plants; check the inside of the plant, not just the surface.

Questions

When is the last frost in the UK?

It varies: from April in mild southern and coastal areas to late May or even June in northern and upland gardens. Check your local forecast rather than a fixed date.

When can I put my houseplants outside?

Many houseplants enjoy a summer outdoors once nights stay above about 12°C, in a sheltered spot out of hot sun. Tropical ones like crotons and marantas are better left indoors.

Should I cut back daffodil leaves?

Not until they have yellowed, about six weeks after flowering. The leaves are feeding next year's bulb.