Dwarf rhododendron ‘Winsome’
The last month of spring is already upon us, with our gardens now bursting full of colour and life. May is the month to plant summer-flowering perennials and shrubs, sow runner beans outdoors and really get your watering and weeding routine in place.
Read our guide to May gardening jobs to find out what to do now, what to plant this month and helpful gardening tips from our Hillier experts to keep your garden at its best.
What to Enjoy Now
Gardening is as much about appreciating the beautiful now as planning and planting for the future. Enjoy these plants in your garden and home this month:
- Spring-flowering climbers: clematis varieties, Hydrangea petiolaris, wisteria
- Spring-flowering shrubs: abutilon, azalea / rhododendron, calycanthus, camellia varieties, ceanothus, Choisya ternata, Convolvulus Cneorum, cytisus, deutzia, exochorda, genista, Hydrangea macrophylla, magnolia, photinia, Spiraea arguta, syringa (lilac), viburnum
- Lavender varieties: Lavandula stoechas (French lavender) and Lavandula angustifolia (English lavender)
- Perennials: acanthus, Anemone sylvestris, aquilegia, brunnera, campanula, delphinium, Dicentra spectabilis (‘Bleeding Heart’), epimedium, erysimum (wallflowers), Fritillaria Meleagris, geranium, tiarella, tulip, primula (e.g. P.beesiana, P. bulleyana), Pulsatilla vulgaris
- Bedding plants: nemesia, pansies and violas
- Alpines: aubrieta, Lithodora ‘Heavenly Blue’, saxifrage
- Trees: amelanchier, Cercis canadensis, cornus, crataegus (hawthorn), magnolia (late-flowering varieties), malus, prunus
Great for Foliage and Structure
- Hostas, heucheras and tiarellas
- Ornamental grasses
- Ferns: aucuba, cotinus, fatsia, physocarpus, sambucus
- Flowering now: Begonias, kalanchoe, orchids, roses
- Great for foliage: Adiantum (and other ferns), alocasia, chlorophytum, cordyline, schefflera, cacti and succulents
What to Plant Now
Vibrant alpine: Lithodora ‘Heavenly Blue’
With the weather getting warmer and risk of frost having passed, there is a lot that can be planted in both the flower and vegetable garden in May.
What to Plant for Instant Impact
Gardening is often about the patient process of growing from seed, bulb or small plant and nurturing it over time. If you want to balance this out with immediate colour, foliage and scale in your garden, you can always find larger plants and those in bloom right now for instant impact.
Simply browse the ‘flowering now’ list above. Many of these plants will be available from the Garden Centre for immediate enjoyment and, once planted, should continue to develop year after year.
What to Plant for Future Interest
- Small herbaceous plants. These can now be planted straight into the garden if it is mild
Hillier Tip: Both 9cm and 1litre herbaceous plants are a cost-effective way to add summer colour to your garden
- Summer-flowering perennials: agapanthus, crocosmia, dianthus, gaura, gazania, leucanthemum, marguerite, osteospermum, rudbeckia, salvia
- Alpines – 9cm or 1-litre plants allow for a cost-effective garden update
- Lavandula angustifolia (English lavender) planted now will flower through summer
- Plant roses now, so they can establish in time for summer flowering
- Later-flowering shrubs, such as hardy fuschia and Hydrangea paniculata varieties
- Mediterranean plants such as cistus and hebe so they can establish as the soil warms
- Plant up hanging baskets ready for summer colour
- The last of the summer-flowering bulbs, like gladioli
- Sow sunflowers, either into a pot or directly into flower borders
Grow Your Own
In May, everything from fruit, vegetables and salad crops, to lawns, flowers and unfortunately weeds, will be in vigorous growing mode. It isn’t too late to sow some vegetable seeds if you haven’t yet — there is plenty of time to grow your own food. Read more about growing this month in our May Guide to ‘Grow Your Own’.
- Sow courgette, marrows, squash and pumpkin seeds into seed cells or individual pots, placed on a light windowsill or in a warm greenhouse
- Vegetable and herb seeds that were sown undercover in April may now be ready to harden off and plant outdoors
- Do this for a period of one or two weeks before planting directly into the ground
- Sow runner bean and French bean seeds directly in mid-May.
Hillier tip: These climbers will need a support to grow up and a wigwam is a simple and attractive solution. Simply place three to four bamboo canes into the ground and tie together at the top. Sow the seeds around each cane at the base – you will only need a single seed at the base of each cane for climbing runner and French beans.
- Plant chilli pepper or sweet pepper plants into the ground, or into containers or small pots if space is at a premium
- Potatoes planted earlier in the year will need ‘earthing up’ to increase the number of potatoes produced. Mound soil around the shoots and cover most of the stems, using the soil that is already there. Repeat every two to three weeks throughout May and June
- Kale (the leaves will still be young), lettuce, peas, purple sprouting broccoli, radishes, rocket, spinach
Hillier tip: See the planting and harvesting times for many of our most loved vegetable and salad plants in our Seed Sowing Calendar.
Other Grow Your Own Activities
- Be vigilant with weeding! Little and often is the key
- Pests such as slugs and vine weevils may be problematic at this time of year. Make sure you have your desired pest control method in place
- Thin out vegetable crops sown outdoors in April by removing young seedlings from crowded areas
- Water – lower frequency and higher volume is best
- Help deter pests in your vegetable plot by ‘companion planting’
Hillier tip: Planting marigolds in your vegetable patch can deter whitefly and also attract ladybirds, which will help to control aphids. They also emit a substance from the roots that deters nematode worms in the soil. Plant nasturtiums alongside your brassicas to attract cabbage white butterflies away from your precious greens. Plant pungent vegetables, such as onions, garlic or chives next to your carrots to deter carrot fly.
What to Do in the Garden
As the weather and soil warms, there are more and more enjoyable activities to do in the garden in May.
Plants to Prune
- Deadhead bedding plants to encourage prolonged flowering
- Deadhead faded spring bulbs
Hillier tip: When deadheading spring bulbs, like daffodils and tulips, leave the foliage in place as this will feed the bulbs for the next year
- Prune penstemons. Cut shoots back to the base of the plant
- Take cuttings from tender perennials
- Prune early-flowering clematis by removing overcrowded and dead stems after flowering
- Prune spring-flowering shrubs that have finished flowering
Plants to Feed
- Feed roses with special rose feed with high potash as they grow. This will encourage a stronger, healthier flower
Hillier tip: High potash feeds are also ideal for tomatoes and fruit trees as they promote strong fruit production and increased sugar levels, meaning higher yields and sweeter fruit.
Plants to Protect
- Limit pest attacks on roses by spraying with a product like Rose Clear 2-in-1 in late May
- When planting any herbaceous plants that have a tendency to grow floppy, add support as early as possible so they will grow up around it
Lawncare & Gardencare
- If you didn’t already, give your lawn a good feed. The best time to apply is when the soil is moist and rainfall is expected
Hillier tip: An all in one lawn product will feed, weed and kill moss. Alternatively, natural products like MO Bacter kill moss and then digest it, turning it into feed for your lawn – and with no need to rake!
- Think about your watering routine. Containers in particular may want regularly watering as warm weather and wind can quickly dry soil
Hillier tip: Always make sure you water at the base of the plant so it reaches the roots. When watering, let the water sink down into the soil then repeat two or three times until the water no longer goes down quickly
- Install a water butt if space allows to collect and recycle rainwater over the coming year
- On warmer days, open greenhouse vents and doors to keep it cool and ventilated and to prevent disease and fungus problems
Birds and Wildlife
Spring is the key breeding season for birds, which means a change in their care and food needs. Migratory birds will be arriving back and will need feeds that are high in protein and essential oils to refuel their bodies after the long flight.
- Give high-protein bird food, like sunflower seeds
- Ensure clean water is available
Monthly Tool Checklist
Some of the essential garden tools and products we recommend to have ready in your shed.
- Digging fork and spade, multi-purpose compost
For earthing up potatoes:
- Trowel or draw hoe
For sowing outdoors:
- Plant labels, trowel, watering can (or hose plus suitable attachment)
- Pruning shears / secateurs
- Lawn mower, edging shears, lawn moss and weedkiller, rake, lawn feed (e.g. Aftercut All-in-one or Viano MO Bacter, which is endorsed by the RHS)