The Ornamental Garden in May


This can be a very busy month subject to what you intend growing.

Providing all fears of late frosts has passed most bedding plants can be planted out this month.

As a rule of thumb, plant out the hardier annuals first, then follow these with the less hardy varieties.


At any time this month:

Inspect lilies for signs of Scarlet Lily beetles which are usually active at this time of the year.

Ensure that tall plants have adequate support.

Keep up with deadheading e.g. Azaleas /Rhododendrons , Camellias, Narcissus, and Tulips.

Plant out Containerised shrubs, Roses and perennials.

Thin out congested Aquatic plants.


Week 18 - 30th Apr. to 5th May.

If not done previously apply a top dressing of general fertiliser in readiness for planting out.

Plant out Aethiopica, Althaea, Azalea, Celastrus, Choisya, Cistus, Escallonia, Euphorbia, Gladioli, Gunnera, Juniper and Roses.

Divide Crepsis, Platycodon, and Thyme if required.

Sow Arctotsis and Calendula seed insitu if soil conditions allow.

If required, plant up planters / containers with Arctotsis and Pelargoniums.

Mulch around permanently planted Alpines, Abies, Lonicera, and Meconopsis.

Commence feeding Abies, Brugmansia /Datura, Cranesbill / Geranium, Echinacea, Kniphofia, Lonicera, and Nerium.

Cut back Buxus, Ceanothus, Cortaderia, Eucalyptus, Hebe, and Jasmine nudiflorum if necessary.

Prune/Tidy up Fatsia japonica.

Prepare beds to receive Chrysanthemums and Dianthus chinensis.

Be on the lookout for Lupin aphid.


Week 19 - 6th May. to 12th May.

Prepare bed for Dahlias.

Plant out Penstemon if conditions allow.

Stop (remove tip) established Dianthus chinensis.


Week 20 - 13th May. to 19th May.

Plant out Asarina, Briza, Catananche, Chrysanthemums, Clarkia, Cornus, Dierama, Eucomis, Helianthus, Incarvillea, Lupin, Ranunculus, and Viola if conditions allow.

Divide and replant Agapanthus, Ajuga, Dierama, Eucomis, Gunnera, Pulmonaria, and Saxifrage if deemed necessary.

Lift, replant or pot up self seeded Lunaria.

Place Canterbury Bells in coldframe to harden off.

Pinch out the growing points of Actinidia arguta and chinensis when quite young.

Do not allow Hamamelis mollis to dry out, Water and Mulch if necessary.

Spray Roses to prevent major outbreaks of pests and diseases.

Deadhead Pieris after flowering.

Cut Narcissus and Tulip down to ground level when the leaves have turned yellow.

Narcissus and Tulip bulbs can be lifted and placed into store for planting elsewhere in autumn.

Commence Chrysanthemum stopping programme.


Week 21 - 20th May. to 26th May.

If not done previously prepare beds for planting out.

Plant out Agastache, Agrostemma, Anomatheca, Arthropodium, Calendula, Callistephus, Carnations, Centaurea cyanus,Chrysanthemum annuals, Dianthus chinensis, Echium, Eschscholtzia, Gaillardia, Godetia, Gypsophila, Helichrysum, Iberis, Lavatera, Limnanthes, Limonium, Linaria, Lobelia, Lychnis, Mimulus, Nemophila, Nicotiana, Nigella, Nolana, Orache, Papaver / Poppy, Phlox drummondii, Portulaca, Reseda, Rudbeckia, Salpiglossis, Salvia, Schizanthus, Silene, Tropaeolum/Nasturtium and Verbena if conditions allow

Place potted Camellias outdoors for the summer.

Layer Wisteria if required.

Divide Papaver / Poppy.

Pinch out the tops of Salvia to encourage branching.

Watch out for signs of leaf spot and rhizome rot on Bearded Iris.


Week 22 - 27th May. to 2nd Jun.

Plant out Ageratum, Alstroemeria, Alyssum, Amaranthus, Antirrhinums, Arctotsis, Bidens, Brachycome, Celosia, Cerinthe, Convolvulus, Cosmos, Dahlias, Gazania, Gerbera, Impatiens balsamina, Ipomea, Pacific Coast Iris, Laurentia, Lewisia, Marigolds, Mesembryanthemum, Nemesia, Nerium, Osteospermum, Pansy, Passiflora, Tagetes, Thunbergia, and Zinnia.

Trim back Aubretia, Choisya, Narcissus / Daffodil after flowering.

Keep Gladioli bed weed free.

Pot up Dahlias to grow as pot tubers.

Feed Aethiopica with a balanced liquid fertiliser at weekly intervals from now until August.


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