May gardening guide: what to do in your garden this May
According to many gardening magazines, May, in the garden, is a joy to behold with new growth and changes happening every day. Fresh new perennials are flourishing, late Tulips are in full bloom, and many shrubs are flowering.
But while spring may be in full swing in the magazines, the weather can catch us out with unpredictable changes from mild spells to low temperatures and chilly winds. Therefore, what exactly it is that you do in your garden in May has to be adjusted for the weather.
May gardening guide: Planting
While gardeners may be keen to get on with planting, it is crucial to keep an eye on the weather. Each spring is different weather-wise. In sheltered parts of Oxfordshire, May is a month when more tender plants can be put outside but not in exposed areas. By and large, everywhere in the county should be frost-free by the end of May, but it is always an idea to have a fleece or cloche handy.
Plant outside in the veg plot
Broad beans, runner beans, peas, onions, garlic, carrots, summer cabbages, brussels sprouts, celery, celeriac, salad crops, leeks and strawberries.
Plant outside in the garden
All hardy perennials and evergreens. In terms of annuals, you can plant out sweet peas and sow hardy annuals such as sunflowers, cornflowers, zinnia, nasturtium, calendula, nigella, and Cerinthe major ‘Purpurascens’ where they are to flower.
Plant out half hardy perennials such as dalvias, diascia and Verbena bonariensis. And continue to plant out summer bulbs such as gladioli to enjoy a continuous supply of flowers late in the summer and autumn.
Sow in the greenhouse
Even in May, the weather can still be cold, and some plants are best sowed under glass or delayed to the end of the month when all risk of frost has passed. These are the more tender vegetables like sweet corn, French beans, squashes, cucumbers, tomatoes, sweet peppers, chillies, aubergine, courgettes and melon.
Plant water lilies into aquatic baskets and gradually lower them to the correct depth over a few weeks.
You can buy tomato plants to grow in the greenhouse in early May or a sunny spot in the veg plot at the end of May when all risk of frost has passed.
By the very end of May, everywhere in the country is usually frost-free, and it is safe to plant out tender bedding plants and non-hardy plants such as agapanthus, canna lily and dahlias.
If you planted dahlias earlier in the year, the growth takes about 6 weeks to reach the surface, which can be around May, and it will need protection if there is frost.
May gardening guide: Care and maintenance
May is the time you can prune early spring flowering shrubs if needed. Pruning helps prevent the shrub from getting too large for its space, and it helps shape it.
These shrubs are pruned only after flowering, so whatever the books and magazines say about the time to prune, it always depends on whether your shrub has finished flowering.
Prune some of the old wood from forsythia, ribes and other spring shrubs as soon as they have finished flowering. Also, prune overgrown camellias hardback if they have grown out of hand.
The ‘Chelsea Chop’
May is ‘Chelsea Chop’ time, which is handy for preventing some plants from getting too big and leggy and with staggering flowering times in others.
The plant needs to be of a reasonable size, and it is important not to chop too early in May - perhaps if the plants have had a delay in their growing stage as a result of a chilly spring.
Administer the ‘Chelsea Chop’ to late flowering perennials such as asters, sedum, phlox and rudbeckia by removing two-thirds of the new growth.
Pinch out the tips of fuchsias to make them bush out and produce more flowers.
Whatever the weather, a job for May is to stake perennials. Ensure that support is in place, and the plant can then be trained through it before it has put on much growth.
Many plants need support, for example, peony, delphinium, dahlias, allium, and anything waving around in the wind looking vulnerable, or with heavy plant heads, such as peony and oriental poppies. The choice of support depends on the type of plant, but make sure any ties used are soft, with room for the plant to grow.
May is also the time to spray your greenhouse with shade paint or put up net shading to prevent overheating. Lay turf or seed a new lawn; showery conditions are ideal to complete this project now. Lower the blades on your mower for shorter grass through the summer unless the weather is quite dry. Hoe between all crops, whenever the ground is suitable, to keep weeds at bay.
May gardening guide: Wildlife and pests
- Make a pile of large stones in a shady part of the garden to give toads and newts somewhere to rest in the shade.
- It’s prime time for asparagus beetles, aphids, cabbage worms, cutworms, scale, slugs, and snails, so watch out.
- Beware of pale yellow Viburnum Beetle larvae that can badly defoliate plants (you’ll find them underneath tattered leaves).
May gardening guide: Other garden tasks for May
- Lift and divide congested clumps of bulbs once the leaves have died off.
- Clean down garden furniture ready for use because summer is on its way.
- Assess your patio for any uneven stones that will need levelling out so that you are ready for BBQ season.
- Harvest salad leaves, asparagus, and rhubarb stems that have been forced under jars by gently pulling them away from the plant’s crown.