Dahling dahlias

GARDENS:THERE ARE TWO kinds of dahlias in this world: the show-offs and the socialites. The first is the one that is grown with as much care as a prize marrow, and which causes as much of a commotion on the display bench at the local flower event. These show dahlias are best grown in glasshouses or polytunnels, so that the weather doesn't spoil their hyperbolic blooms. I've never grown these, but my friend, Jane Ebrill, took the trophy for best-flowers-in-show with her dinner-plate sized 'Kelvin Floodlight' blooms a few weeks ago. If you have the space, these outrageous varieties of dahlias will bring a smile to your face and to that of everyone else who sees them (except the other competitors).

For the rest of us, there are other, more gregarious dahlias. These are pretty jazzy looking in their own right, but they still manage to get along with other plants in the garden. They include fruity-coloured varieties such as red ‘Bishop of Llandaff’, orangey-caramel ‘David Howard’, maroon ‘Nuit d’Été’, near-black ‘Arabian Night’ and spiky, cherry-toned ‘Hillcrest Royal’. They are all noisy, noticeable plants, but their blooms are not over-large or ostentatious. They animate a border, making welcome and lively remarks, and are much appreciated at the tail-end of the summer. Joining these bright characters in popularity now are the more subdued species dahlias, with simple, single flowers. Among them are the pale lilac D. merckii and D. sherffii, and a mixed bag of crosses with the red-flowered D. coccinea, that may be any shade from scarlet to light peach. They are not easy to find in garden centres, but some companies sell their seeds, including BT World Seeds (b-and-t-world-seeds.com) and Thompson Morgan (thompson-morgan.com).

Border dahlias start to flower around July, and go on until frost knocks them down in autumn. For decades they were deeply unfashionable plants, but now they are the height of sophistication – particularly the species kinds.

Growing dahlias

You can buy dahlias in flower around now, but it’s cheaper to get tubers in spring. Start them off in large pots of compost, so that the tubers are at least 15cm below the surface. We use 30cm (or larger pots), and put a trowelful of well-rotted manure, or something nutritious, at the base of the container first. You can also plant them straight into the garden in late March or April, but the emerging shoots are likely to become breakfast for slugs and snails. Dahlias are tender, so if frost is predicted, protect them overnight with horticultural fleece, burlap, or any permeable material. The idea is to let the plant breathe, but to stop ice crystals from settling on it. If you have your dahlias in pots in a greenhouse, polytunnel or even a sunny porch, they should have enough protection (except in a severe winter such as the recent one).

Pinch out the growing tips when the plants are about 30cm tall, to encourage them to grow bushier. Don’t let them loose in the garden until after your last frost date – which can be early May in warm and coastal areas, and up to mid-June in colder areas. If you have started them in containers, you can either plant them into the ground, or keep them in pots, standing them in beds where there are gaps.

Dahlias are thirsty plants, so make sure that they get enough to drink during the growing season. In poor soils, add some manure (pelleted poultry manure is fine) to the planting hole. Stake the stems if necessary. Keep removing the spent blooms, so that they go on producing. When frost finally hits them in autumn, cut back the stems to near ground level, dig them up, let the tubers dry off, and store in dry compost or sand, in a cool place. In mild areas with free-draining soil, you can leave them in the ground. However, if your garden is thickly planted, earlier plants will crowd them out in spring, so lifting might be a better idea.

Good companions

Dahlias mix well with plants that are bold of leaf or flower. Together they combine to make a strong and vibrant scene, like a child’s drawing, or an imaginary jungle. Among those that make happy partners are bananas (Musa basjoo and Ensete ventricosum), cannas, castor oil plants (Ricinus communis), and some lilies. When choosing lilies, avoid dwarf kinds and those with upward-facing blooms, as they offer too much competition. Dahlias also associate well with certain woody plants: those that can be “stooled”, that is, pruned back to near ground level in spring, after which they produce foliage that is usually larger and more architectural than that of unpruned specimens. Among these are acacia, catalpa, cotinus, eucalyptus and paulownia. Grey-foliaged artemisia, and the blue-green, serrated Melianthus major make cool foils for hot-coloured dahlias. Ornamental grasses, particularly those that take on buff tones in the second half of summer, are also sympathetic comrades.

Dahlia date

Today (Saturday, August 28th), 3-5pm: Delgany and District Horticultural Society dahlia show and plant sale at St Patrick’s School, Church Road, Greystones, Co Wicklow