May is a good time to plant out cannas and dahlias. Tubs can be planted up with summer bedding in milder areas. Be sure that all risk of frost has passed.
Wallflowers, pansies, and daisies, Bellis perennis and winter bedding plants need to be sown between now and July in order to flower next spring. Faded wallflowers and spring bedding from beds and containers must be removed in order to make space for summer plantings.
Divide clumps of herbaceous perennials which needs propagation. Divide bamboos and clumps of bulbs or rhizomes in the same way.
You can cutback clumps of spring-flowering perennials such as Pulmonaria and Doronicum and encourage a fresh flush of foliage. Primula can be divided after flowering and hostas as they come into growth.
Trimming back the annuals like Lobularia and perennials like Alyssum or Aubrieta after flowering can help you to encourage fresh growth and new flowers.
Over- crowded clumps of daffodils must be lifted and divided after they have flowered.
Do not forget to deadhead tulips and daffodils.
If you would take cuttings of Argyranthemum, Pelargonium and Fuchsia they will provide new plants for display later this summer.
Propagate perennials that are showing new shoots from the crown via basal stem cuttings.
Your garden needs some general maintenance in spring, hence it’s important to apply a liquid fertiliser to spring bulbs after they have flowered.
Let the foliage of daffodils and other spring-flowering bulbs die down naturally.
Put supports in place and control herbaceous plants.
Hoe borders to prevent annual and perennial weeds from spreading and seeding themselves.
Liquid feed plants in containers every two to four weeks. Tubs, hanging baskets and alpine troughs must be well watered.
Pests and disease watch has a big role this month. Vine weevil larvae can become active now.
Aphids can multiply rapidly during mild spell. You can remove early infestations by hand. Continue lily, delphinium, hosta and other susceptible plants protection from slugs and snails.
Remove dead leaves from around the basal rosettes of alpine plants to prevent rotting.
Fertilize spring-flowering alpines with grit or gravel to show off the plants and help prevent rotting around the neck.
Primarily, look round for BOX TREE MOTH, because they can completely defoliate box plants. It’s relatively NEW insect to Britain.
Cut back Penstemon, Caryopteris and Fuchsia after the danger of frost has passed and clip evergreen hedges. Young mimosa trees can also be cut back now.
Prune spring-flowering shrubs after flowering. Evergreens such as Viburnum tinus can also be trimmed this month. Prune overcrowded, dead or diseased stems of Clematis montana after flowering. Prune out frost damage from affected evergreen shrubs. Late spring is a good time to coppice or pollard Eucalyptus.
Remove any reverted green shoots on hardy variegated evergreens, to prevent reversion taking over.
Wall-trained pyracanthas needs to be pruned by removing any shoots coming out from the wall, and shortening other new growth to about 8cm.
Tie in climbing and rambling roses horizontally.
For trees and shrubs general maintenance you’d need to protect newly planted ones from drying out by watering them with rainwater or recycled water (wherever possible).
Take softwood cuttings of deciduous shrubs. Layering is a good way to propagate climbers and lax-stemmed shrubs.
Check roses for signs of blackspot. Inspect sick looking box and holly trees for signs of blight.
Caterpillars, aphids and other fly pests can all be problematic in Spring time. Early infestations can be removed by hand. Check for damage or cankers on deciduous trees too.
Mow regularly and continue adding clippings to the compost heap. Apply a high nitrogen summer lawn fertiliser to encourage a healthy-looking lawn.
You can sow new lawn in early May. Prepare the ground by cultivating, levelling and lightly firming beforehand.
Do not walk over or mow newly sown grass until it has reached a height of 5-7.5cm and then give it a light trim at the highest setting.
Protect new lawns from drying out during dry spells.
If moss is a problem, choose a combined fertiliser and mosskiller when feeding the lawn.
You can still plant new aquatic plants this month. Thin out, cut back or divide excessive new growth on established aquatic plants. Top the surface with a layer of gravel to prevent the fish from stirring up the compost.
Begin stocking ponds with fish when new plantings have established. Avoid introducing goldfish to wildlife ponds.
Remove blanket weed by twirling around a rough stick and skim off floating weeds with a net.
Remove algae from paths with pressure washer. Remove dirt and algae from walls, paving and patios. Check and repair pergolas, arbours and arches if needed.
You can treat timber structures with wood preservative and stain in dry spells. Make sure you use appropriate products.
Go through your shed and remove any old, out-of-date garden chemicals.