Blossom, spring bulbs, and the fresh green of new buds: the month of May brings all these delights to our gardens. But don’t allow your excitement about the growing season ahead to fool you into assuming it’s summer already: this is the month when holding back can pay off in the long run. It’s still too cold for many tender plants to go outside fulltime, so the game of Tetris continues, shuffling plants in and out on sunny days and shoving them anywhere and everywhere inside at night. And let go of your mower, too: leaving lawns to go wild allows all kinds of delights to flower, much to the joy of the bees.
Five things you should plant
The deep purple flowers of Salvia Amistad start in early summer and keep coming through to the last gasp of autumn, making this herbaceous perennial a must for any sunny, sheltered spot. The foliage is aromatic, and the tall stems make a great cut flower – although leave plenty for the bees, who adore this plant.
If you are looking to clothe bare soil in a shady spot, ground cover plants don’t come much better than the foam flower, AKA Tiarella. These produce spires of pale pink frothy flowers each spring, atop pretty foliage. Cultivar Spring Symphony makes a dependable choice, as it has an RHS Award of Garden Merit.
The Japanese pepper (Zanthoxylum piperitum) makes an unusual, easy and hardy garden shrub (height and spread 2m x 2m) that produces an annual autumn harvest to bring joy to any foodie: clusters of zingy peppercorns. Its other name is prickly ash, which should warn you of a potential drawback – it’s spiny.
Comfrey is a wonder plant – its tap root draws up nutrients from deep in the soil, and the leaves store nitrogen, phosphorus and potassium, making them perfect for use as fertiliser. You can harvest this foliage to make a liquid plant feed, add as a surface mulch or add to planting holes. Cultivar Bocking 14 is the one to go for because it is sterile (meaning it won’t self-seed around) and will grow in any vacant corner.
If you plant just one edible in your garden this year, make it the Welsh onion, Allium fistulosum. This perennial vegetable can stand in for oniony relatives you have to sow every spring, such as spring onions, chives and bulb onions. If you let it flower, bees love the round white flowerheads. Either grow from seed or buy young plants.
Five garden maintenance tasks to complete
At some point this month there is a tipping point: the risk of frost passes, and all the tender plants you’ve been tripping over indoors can be planted outside. Keep an eye on the weather forecast and look for a rise in night-time temperatures – tomatoes, for instance, need a minimum of 10C night and day before they can go out into a bed or container. While you’re waiting, harden off summer bedding and other tender plants in preparation for their transfer outside: this means putting them outside somewhere sheltered on warm days to gradually adjust to the conditions. Remember to bring them in before the temperature drops at night.
The moment the risk of frost passes is also the point that you can start sowing crops such as courgettes, squash and beans directly into the ground, and you can also plant out seedlings sown earlier this spring or bought from garden centres. Cover with a cloche or some horticultural fleece to give some extra protection from the weather and from slugs.
Climbers such as clematis, sweet peas and passion flowers will be putting on spurts of growth now, so take five minutes to tie in new growth to their supports, whether that’s an obelisk, trellis or a pergola. Use garden twine, or thin strips of old T-shirts, which are soft enough to avoid damage to stems, in a figure of eight shape to attach the stem to the support with the knot on the support side. Try to ease stems as close to a horizontal position as possible: this encourages flower buds to form.
May is also the month for that brutal-sounding gardening technique, the Chelsea chop. It’s a way of staggering the blooming of plants that flower in bursts over the summer such as rudbeckias, catmint (Nepeta), echinaceas and heleniums. You can either cut every plant back by a third, or restrict your trimming to some clumps and leave others: either way, it should create bushier plants that flower over a longer period. The moment to do this will vary depending on your local conditions, but make a note in your calendar for the end of May (when the Chelsea flower show traditionally takes place, as long as it’s not postponed by Covid).
It’s tempting to rid your garden of the fading foliage of spring bulbs once the flowers are gone, but these leaves are sending resources back into the bulb to make next year’s blooms. Leave foliage in borders once you can lift them away with no pressure. Do deadhead though, cutting back flowering stems to the base once the display is over.
Five other ways to enjoy your garden
Reptiles and amphibians don’t usually figure prominently in garden wildlife advice, and yet they are fascinating and beneficial for your garden. Attract slow worms and common lizards by leaving areas of long grass and piles of logs, and placing a sheet of corrugated roofing material or pieces of slate in a sunny corner. Ponds are magnets for frogs, toads and newts, and now’s a great time to build one – check out wildlife writer Kate Bradbury’s new book How to Create a Wildlife Pond for a step by step guide.
You may not spot vine weevils around the garden, but you’ll see the damage they cause. The adults munch irregular notches from the edges of leaves, while the larvae do the real damage below the surface by eating plants’ roots. They particularly love heucheras, strawberries and primulas and if left unchecked can kill whole plants. Nemasys vine weevil killer can be applied once the soil temperature reaches a steady 5C: this biological control uses a microscopic nematode worm to kill the larvae, and is safe for use around children and pets.
Why not set up a wormery in your garden this spring? It is a great way of handling food waste, producing wormcasts and a liquid runoff, both of which can be used to feed plants. You can make your own wormery using plastic boxes, or invest in a bespoke wormery; the best ones come as a set of stacking trays so the wormcasts can be harvested easily, and are made of recycled plastic.
Thinning out young plants is a necessary evil when it comes to both vegetable crops and annual flowers. If you leave seedlings bunched together, they outcompete each other and the result is stunted growth. For vegetables such as carrots and beetroot, you can eat the pickings; for annual flowers such as love-in-a-mist, pot marigolds and cornflowers, carefully dig up the excess seedlings with their roots intact and you should be able to transplant them into any bare patches.
Here’s a job to avoid this month: lock up your lawnmowers for No Mow May. This campaign by charity Plantlife encourages individuals and local councils to let grass in parks and on verges go wild for a few weeks, allowing dandelions, daisies, clover and other flowers to come into bloom and provide valuable pollen and nectar for bees and other pollinators.