Dahlias have a long history as garden plants and today there are over 50,000 different dahlias in cultivation, in a huge range of shapes sizes and colours. Growing dahlias is generally easy but they should be treated as half hardy perennials in most areas, and in frost prone areas it may be necessary to lift the tubers to overwinter dahlia plants. They may also need protection from pests and diseases. An exciting bonus when growing dahlias is that it´s easy to breed new dahlia varieties.
Care and Cultivation of Dahlias
Dahlias will grow in almost any situation, but give the best results in full sun and a good loam soil enriched with plenty of organic matter.
Some varieties are sold as seed but since dahlias don´t breed true from seed, they are normally sold as tubers (some people know them as dahlia bulbs) or pot grown cuttings. When growing dahlias, from whatever source:
- Some gardeners prefer to set them out in informal groups in a mixed border, but they lend themselves to more formal plantings in beds set aside exclusively for dahlias.
- If growing them purely for cutting, set them in rows to allow easy access and tying in.
- Treat them as half hardy bedding plants in their first year, starting the dahlia tubers into growth under glass, and not planting out rooted cuttings or sprouting tubers until after the last frost.
- To start tubers into growth, bury them in trays of dry soil, sand or compost, with just the old stem showing in a cool, dark frost free place, like a garage or shed, or under the greenhouse bench. Bring them into full light when the first new shoots are half an inch or so long.
- In Britain, sow dahlia seed in greenhouses in February-March, planting out the seedlings after all risk of frost is past.
- Plant them out where they are to flower in May, and stake medium and tall growers immediately, as they’re very vulnerable to wind damage.
- For a normal garden display, they’ll then look after themselves for the rest of the season, with just the occasional dead-heading, tying in and tidying.
- For show-quality blooms and for cutting, feed regularly with a high potash liquid feed, such as a tomato feed, and disbud for fewer, larger flowers.
- As the autumn frost approach consider whether your dahlias need frost protection to overwinter.
Dahlia Pests and Diseases
Unfortunately dahlias are vulnerable to a number of pests and diseases:
- Slugs.Gardeners may have divided views about dahlias, but slugs don’t. It’s vital to protect the fresh young shoots with slug pellets or, if you don’t approve, your own patent remedy.
- Earwigs. Earwigs, too, love dahlias, attacking the buds and flowers. Clear away debris where they may hide, and try the traditional remedy of the upturned flowerpot on a cane. Then, each morning, dispatch any that have hidden in the pot overnight.
- Aphids.Aphids not only attack the fresh shoots and buds, but also expose the plants to disease. Spray early and often.
- Fungal Infections.Dahlias are vulnerable to rot and mildew, but also watch out for mosaic and spotted wilt, producing stunted, discoloured plants. Controlling aphids, which carry the diseases, gives some protection, but there’s no cure, so lift and burn any infected plants immediately.
Breeding New Dahlias
As dahlias hybridise so readily, it’s very easy to breed new varieties, and there’s always the chance - however remote - that even a novice may produce a stunning new variety.
- At the most basic level, all you need to do is gather the seed from ripe, randomly fertilised flower heads.
- To be a bit more ambitious, choose two promising parents and use the pollen from one to fertilise the other (first removing the stamens from the pollen recipient and protecting the stigma from random fertilisation with a plastic bag). This will only improve the odds very slightly, but it’s fun to experiment.
- Whichever the method chosen, sow the seed in early spring and see if any of the seedlings produce anything interesting. One might just be a Chelsea Show stopper!
Tony Allen - In 2004 I began my "fourth career" as a freelance writer. In my first career, after training at the Royal Military Academy Sandhurst, I ...
