May in the Garden
Summer is just around the corner! The work you do now will pay dividends later in the season.
Herbaceous Perennials, Bulbs and Annuals
Dead-head spring flowering bulbs and lift those in positions where the space will be needed for summer flowers. They can be transplanted into the vegetable plot or into containers. Allow the foliage to die back naturally, unearthing and cleaning them only when the leaves have withered completely.
The gaps left can be filled with plants such as amaranthus, dwarf rudbeckia, dianthus or nicotiana for late season colour in August and September. Tender perennials such as Argyranthemum ‘Jamaica Primrose’ in yellow and pink anemone-centred ‘Vancouver’ also work well, growing rapidly to fill border gaps.
Plant out rooted cuttings and sprouted dahlia tubers towards the end of May when there is no longer a risk of frost. If your local climate is mild, you may be able to do this in early to mid-May. Dormant tubers can be planted from mid-April to grow on at the end of May.
The earliest and largest ornamental onions, such as Allium stipitatum, A. giganteum and A. ‘Purple Sensation’ are at their best now and in early June. Don’t dead-head unless you want them for dried flower material or to save seed. Collect the seed and sow in pots. Ripe seeds will germinate easily and the wait of 3-4 years for flowering plants is worthwhile, given the magnificent May display that will result. Although tall at flowering time, these Alliums are at their most dramatic at the from of a border, and look most attractive against a contrasting grey-green backdrop, such as that created by a carpet of Geranium renardii.
Deciduous Trees, Shrubs and Climbers
Many trees and shrubs look at their most beautiful now. Some will benefit from pruning as soon as they have finished flowering, to ensure the production of new, flowering wood. Spiraea arguta and Kerria japonica both benefit from reemoving weak, old, or crossing wood to keep them tidy, but make sure you go one step further, cutting back all flowered stems to vigorous young growth further down the plant. For the best display, cut back one stem in three right back to ground level each spring. This will encourage new grouwth and keep the shrub tidy and well-formed.
The flowered stems of Cytisus should be cut back to half their length, but avoid cutting into older wood.
Hawthorn is perhaps the most iconic of all spring-flowering shrubs. Varieties such as double crimson, Crataegus oxycantha ‘Paul’s Scarlet’ or double pink ‘Rosea Flore Pleno’ introduce wonderful vivid colours into the spring garden. However, these can grow to as much 6m in height and spread, so they may not be suitable for smaller gardens. More compact forms include C. ‘Stricta’ and the weeping pink C. monogyna ‘Pendula Rosea’ are ideal for smaller spaces. Hawthorn also works well when grown over arches or around doorways. It should be clipped back each year after flowering to ensure it stays close to the structural support.
Summer Container Planting
Remove spring bedding plants from pots and window boxes to make way for summer varieties, and refresh the compost by replacing the top few inches. Replant after the last of the frosts in your area. When shopping for summer bedding, pick out compact, sturdy plants, rekecting any that are drawn, wilted or pot-bound.
In addition to old favourites such as lobelia and busy lizzie, consider newer additions to the planting catalogue, such as newer varieties of Begonias, such as the gorgeous’Glowing Embers’ (left).
Planting a Hanging Basket
Hanging baskets can be planted up now and left to grow in for a few weeks in a greenhouse or conservatory, to give a good display from the moment they are hung outdoors in late May or early June.
Top up with the compost to half way, then insert a second tier of plants so that they do not directly overhang the first row.
Fill to the rim with compost and place upright plants in the centre of the basket, with trailers towards the edges, and water the basket thoroughly.
In the Greenhouse
Support tomatoes by tying then in to canes, or by twisting the stems round suspended strings anchored into the compost. Pinch out the lateral growths of cordon varieties and start to feed weekly when the first fruits begin to swell. Ventilate the greenhouse on sunny days when temperatures under glass can soar, but always close up at night.
This is your last chance to sow melon seed. Plant out peppers and aubergines into 22cm and cucumbers into 25cm pots or into grow bags.
For a good spring and early summer display in the garden next year, sow seed of wallflowers, foxgloves, fotget-me-notss, sweet william, polyanthus and canterbury bells. Prick out the seedlings into trays and grow them on until they are ready for planting out. These young plants are easily overlooked in strongly growing sunner borders, so if you have room, line them out in a nursery beed and transfer them to their flowering positions in September or October.
The Edible Garden
This is a busy time in the kitchen garden. Many vegetables that have been started off in the greenhouse, or even on the kitchen window sill, can be hardened off slowly via cold frames and eventually planted out. To do this, remove the covers during the day and replace them at night for several days until the plants have become acclimatised to the outdoor climate and are ready for planting out into their final positions.
Keep picking Swiss chard (seakale beet) this month. The advantage it has over spinach is that you can sow it from April through July to crop in autumn and the following spring and it won’t start to bolt before then. Always sow a new crop each year to be assured of a continuous supply of leaves. Cut or break off the leaves at the base, trying not to leave any portions of the thick white stems to rot and affect the rest.
For the table, stems can be cut away from the leaf blades and cooked separately like celery. A light steaming for both leaf and stem keeps in the flavour.
There’s still time to sow beetroot and if you sowed a good standard variety such as ‘Boltardy’ last month, try some of the more unusual varieties such as ‘Chioggia Pink’ and ‘Albina’.
Start sowing French beans outside. A good method is to sow two rows 45cm apart in drills 5cm deep, with a spacing of 10cm between the seed. ‘Purple Queen’ looks as good as it tastes. There are many good greem varieties to choose from, but the key to good flavour is to pick while still young.
Runner beans sown indoors can be planted out from mid-May keeping an eye our for late frosts. Or sow directly into the ground towards the end of the month in colder areas. The ground should have been well manured and supports rigged before planting or sowing. Plants should be 25cm apart and can be grown in rows or to climb up a circular wigwam structure.
Many of the runner beans have particularly attractive flowers. The old-fashioned variety ‘Painted Lady’ has striking red-flushed white flowers, while ‘Scarlet Emperor’ is a heavy cropper with deep red flowers and is popular for its flavour. The modern white flowered ‘Desiree’ produces almost stringless long green pods.
Winter salads can be spiced up with chicory sown this month. Roots should be lifted in October or November for forcing. Varieties like traditional ‘Brussels Witloof’ and ‘Apollo’ are all tasty options.
For summer salads keep sowing lettuce and radishes at fortnightly intervals. Plant outdoor tomatoes towards the end of this month and support with canes, bush varieties may only need a short cane.
Sow sprouting broccoli in seedbeds to transplant later for winter use.
Apples, Pears, Peaches and Berries
Never allow young trees to carry full crops or it will stunt their growth. Limit the number of fruits to just a few by picking off unwanted fruitlets.
Hang special codling moth traps in apple trees late in the month. These attract and catch the male moths.
Keep the new canes of blackberries, loganberries and tayberries separating from the fruiting canes by tying them vertically above the plant so that they are less likely to be infected by any diseases the fruiting ones might have.
When the fruitlets on fan-trained trees are about the size of a hazel nut, thin them out to leave just one every 10cm or the ultimate size will suffer.
Look out for attacks of red spider mite late in the month and greenfly at any time and take action as soon as they are spotted.