Dahlias in the garden of Sandra Wilson in Sydney

I find it hard to believe it now, but I once hated dahlias! I regarded them as rather uncouth and the province of deranged gardeners who only wanted to see how big they could grow the flowers in order to win a competition. I never imagined that one day they would be amongst the stars of my summer garden. The turnaround is mainly due to my evolution from wanting to grow traditional English border plants to an appreciation of how warm-climate plants are far more suited to our hot, humid Sydney summers, which proved anathema to the delicate Northern Hemisphere perennials I once delighted in. Dahlias are also in fashion in UK gardens now, thanks to the enthusiasm of gardeners such as the late Christopher Lloyd, who used them with other exotic plants to create brilliant and exuberant borders.

Tall dahlias in the garden of Sandra Wilson in Sydney

Tall dahlias in the garden of Sandra Wilson in Sydney

I haven't (yet) embraced dinner plate-sized show dahlias, which just don't blend in easily with most other plants, but the smaller-flowered ones form telling clumps in my garden and provide colour over many months: from November to May, but looking particularly good right now. Tuberous perennials of the daisy family (Asteraceae) from Mexico and Central America, they are perfectly at home in Sydney. Few other plants can match them for flower power! Last week I visited the garden of a friend, Sandra Wilson, who lives not far from me, and was overwhelmed by the number of dahlias she had growing, varying from low-growers only 30 cm in height to others that towered over my head. The hues of the petals range from crisp white through various shades of pink and cerise to deep reds, yellows and oranges, the latter hues being wonderful for 'hot-coloured' borders; a number of the flowers have two or more colours in the petals, combined as if in a watercolour painting.

Waterlily-flowered dahlia in the garden of Sandra Wilson in Sydney

Waterlily-flowered dahlia in the garden of Sandra Wilson in Sydney

Whilst many of the blooms are of single form, others in the garden are of the 'cactus', 'waterlily' or 'collarette' types, underlining the mindboggling diversity of dahlias. The blooms mingle in glorious profusion with the many other flowers of late summer in her garden: such as roses, Salvia, Geranium 'Rozanne', perennial Aster, Pentas, early Plectranthus varieties, Tibouchina and Justicia species. The tallest of the dahlias jostle good-naturedly with some lofty self-sown Zinnia flowers, fellow members of the daisy family, which provide a similarly long period of summer colour.

Dark-leaved dahlias in the garden of Sandra Wilson in Sydney

Dark-leaved dahlias in the garden of Sandra Wilson in Sydney

In recent years, many gorgeous new cultivars have become available in nurseries, including some with alluring dark foliage. The classic 'Bishop of Llandafff' (which was a chance self-sown seedling named in the 1920s by Cardiff nurseryman Fred Treseder) with its stunning red flowers was one of the first of these. I was amazed to learn that lots of the lovely ones in Sandra's garden were also self-sown seedlings, descendents of her original plantings from years ago. It certainly pays to keep an eye out for chance seedlings in the garden.

Two-toned dahlia in the garden of Sandra Wilson in Sydney

Two-toned dahlia in the garden of Sandra Wilson in Sydney

Dahlias like a sunny position in the garden, with rich, moist (but well-drained) soil. They'll appreciate organic matter dug into the soil at planting time; and a fertiliser applied in spring will help them grow vigorously. Occasional feeds of a water-soluble tomato fertiliser during the growing season promote flowering; as does conscientious removal of all the spent flowers. I find it quite therapeutic to snip these off every few days, and it makes a big difference to the appearance of the plants as well! If you'd like some seedlings, leave a few deadheads on towards the end of the flowering period in autumn. Tall-growing forms require support: I use metal cradle stakes, but canes can be used and the plants tied to them with twine. Pinching the growing tips back early on in the season helps develop a stockier plant.

Self-sown dahlia in the garden of Sandra Wilson in Sydney

Self-sown dahlia in the garden of Sandra Wilson in Sydney

Sandra leaves the tubers in the ground over winter, a practice which generally works well in Sydney, as we don't experience the severe cold that necessitates the nuisance of digging them up and storing them over winter that is required in cooler climates. Whilst they are dormant, there is a gap in the garden; however, in Sandra's garden self-sown spring annuals such as poppies colonise these areas to provide a pretty display. In my own garden, I have taken to sowing seeds of shallow-rooted, fast-growing edible winter crops, including rocket and coriander, on top of my dahlia bulbs. This year I am planning to try mizuna (Brassica juncea) and corn salad (also known as lamb's lettuce, Valerianella locusta) as well. By the time these crops are exhausted, the dahlia bulbs are beginning to sprout again.

Cactus-flowered dahlias in the garden of Sandra Wilson in Sydney

Cactus-flowered dahlias in the garden of Sandra Wilson in Sydney

The tubers get rather congested after a while so need to be dug up and divided every few years around September (before they start to sprout) and replanted in soil which has been amended with plenty of compost and decayed manure. When the tubers are divided, each portion needs to have part of last year's stalk attached, or it will not regrow. Dahlias can also be propagated by taking cuttings of the new foliage shoots spring, which will grow quickly to form new plants. Dahlias make good cut flowers, as long as the cut end of the stem is sealed by being dipped briefly in boiling water.