Dahlias are part of the daisy family. Sometimes they are referred to as the “queen as daisies”. There are societies devoted to the growing, cultivation and hybridisation of the flowers, including the “Dahlia Society of Australia”.
Dahlias are named after Andreas Dahl, a Swedish botanist. The original dahlias were from Mexico, and came in two basic forms: a single row of petals around an open centre, or “doubles” – two or more rows of petals around an open centre. Seeds of dahlias were introduced into Europe, through Madrid, in the eighteenth century and quickly became popular with plant breeders who began producing hybrids almost from the moment of their introduction!
Dahlias easily cross pollinate, creating new hybrids. Seed doesn’t necessarily produce true to type so there are often surprises in the garden which makes them really popular with breeders as they feel compelled to try for new and better blooms.
There are dahlias in just about every colour imaginable, except blue, which the breeders are still attempting. These can be one colour or bi-colours. Flowers styles have been increased from the original open-centred varieties to include cactus, ball and pompom types, as well as waterlily, paeony, chrysanthemum and anemone varieties. There are dahlias that can be grown in different climates and soil types; varieties that bloom early and those that bloom late. They can be tall or miniature. No wonder they are beloved by so many people.
Dahlias grow from tubers (swollen roots). They are herbaceous and perennial; dying down in winter and reappearing in spring or summer (depending on variety). In mid-summer, we have flowers in bloom, plants that are finished for the season and plants that have yet to come into bud and will flower well into autumn.
HOW TO GROW DAHLIAS FROM SEED OR TUBERS
We have found growing dahlias from seed an easy process. Follow the directions on the seed packet. If you collect your own seeds, sow the seed in late winter or early spring at a depth equal to about twice the width of the seed (shallower is better than too deep). Keep the seed-raising mix moist but not wet or the seed may rot. You will need to protect the seed from slugs and snails – we have lost many tiny seedlings due to their voracious appetites.
Move your baby seedlings from the seedling tray to their own pots when they are big enough to handle, generally about four weeks after germination. Choose a location for your plant where the soil is free draining and the plant gets full sun, although young plants like a little shade in the heat of a summer afternoon.
Transplant the young seedling to its location in the garden when it is about 10cm tall. Pinch out the growing tip to help the plant become more bushy. During hot, dry weather, give your plants water as needed. Do not overwater but remember, plants grown from seeds have not yet developed a tuber, so they will need more frequent water than plants grown from tubers.
You can buy named varieties or plants simply labelled “dahlia” or even “bedding dahlias” in pots in the garden centre, generally when they’re in flower so you can see exactly what you are getting. Tubers can be bought in late winter at some garden centres on from online mail-order catalogues. Plant these according to the directions that come with the tubers. If transplanting a potted plant, put it in the ground as you would any other potted plant, the soil level of the pot being the same as the level of the soil in the ground.
At Hillside, in the foothills of the Blue Mountains, in western Sydney, we leave our tubers in the ground all year, only lifting them to divide them or to move them to another part of the garden. If you live in a wet climate, have drainage problems in winter or your land literally freezes, you will need to lift the tubers and store them in a cool, dry place.
FUN FINAL FACT
The tallest variety of dahlia is Dahlia Imperialis, the tree dahlia, which can grow as tall as 5 metres!
The smallest dahlia grows to about 30cm.