Plan to add dahlias to your garden
Quintessential cut flower alive with colour and variety
Just when summer feels like a distant memory, my screen is filled with brilliant red, orange and pink dahlias captured last summer in the Chicago area — it’s the perfect tonic for a blustery January evening.
Dahlias are the quintessential cut flower, but they also make showy additions to flower borders and container gardens. The National Garden Bureau named 2019 the year of the dahlia. Let’s take a closer look.
The native dahlias, found in the mountains of Mexico and Guatemala, are the genetic source for the modern hybrid dahlias we grow today. Today the dahlia is the national flower of Mexico. The Madrid Botanical Gardens named the genus for Andreas Dahl, a Swedish botanist and student of Carl Linnaeus. Initial breeders of dahlias were more interested in the dahlia as a food source since the blooms at that time were not particularly noteworthy.
In 1872 a new box of dahlia roots was sent from Mexico to Holland and the only surviving tuber produced a brilliant red bloom with petals that were rolled back and pointed. Immediately dahlias regained their place on the benches of plant breeders.
These progenies have served as the parents of today’s hybrids. Breeders today propagate new cultivars using various techniques and creating fantastic new colours, shapes and plant habits that perform well in the garden.
Dahlia is a genus of tuberous plants that are members of the Asteraceae (or Compositae) plants; related species include the sunflower, daisy, chrysanthemum and zinnia. There are many species of dahlia in a range of colours and forms with hybrids commonly grown as garden plants. The flower varies in size and form, ranging from five centimetres in diameter to up to 38 cm. The largest flower form is informally known as a “dinner plate” dahlia.
There are several ways to enjoy your first dahlia. Most major garden centres, home improvement stores and mail-order sources sell dahlia tubers (a thick, underground stem or rhizome) as well as blooming potted plants. A tuber looks like a sweet potato that grows under the soil surface and sends up strong stems.
Dahlias can also be grown from seed. Stokes Seed catalogue offers Harlequin and Figaro dahlias in a variety of colours and a manageable size (about 30 cm tall). They would be ideal for planters or edging the flower garden. Taller varieties such as Sunny Reggae (51 cm) in shades of yellow, orange and scarlet, and Large Flowering Double Mix (90 cm) with heavy flowers that should be staked are both worth a try in the home garden.
Seed-grown dahlias are a very economical way to fill your summer cutting garden with colour. Dahlia seed should be started about the middle of February until the middle of April for July blooms.
Dahlia tubers can go directly into the ground in the spring when the ground is warm and there is little chance of frost. One good guideline is to plant at the same time as you would a tomato. If you want blooms as early as possible, you can start the tubers indoors in good light about a month before planting time.
Last spring, I experimented with my dahlia tubers. Half were started in our little greenhouse and planted out in early June, the rest were planted directly in the ground. The tubers that were planted directly in the ground started slow, but really took off once the warm weather arrived — they actually bloomed before the tubers that had a head start in the greenhouse.
Dahlias require a site with good drainage and partial to full sun. Tall dahlias need to be staked to avoid falling over when the heavy blooms appear. Best practice is placing the stake prior to planting to avoid damaging the tuber and roots system. Sturdy tomato cages or bamboo teepees offer a simple approach to staking.
Plant the tuber according to the package directions with the “eye” on the tuber facing up. The eye is the point on the shoulder, or crown, of the tuber from which the plant grows. If you are buying potted plant dahlias, simply transplant into a prepared garden bed or decorative containers.
Small dahlia plants are susceptible to slug damage and Japanese beetles seem to enjoy dahlia blooms just when they are ready for a bouquet. One of the best methods of control is to manually remove the beetles and drop them into a bucket of soapy water. Dahlias are not “deer-proof,” but they are deer-resistant.
Dahlias do not need a lot of water; in fact, excessive watering early in the season can lead to rotting. Best practice is to monitor the soil moisture especially if the local rainfall is less than three centimetres per week. Container-grown dahlias will need daily watering.
Dahlias will generally benefit from regular treatments with a water-soluble or granular fertilizer. Traditional wisdom for dahlias is to treat with a high nitrogen fertilizer early in the season and then transition to a bloom-type fertilizer in the middle part of the season. You should stop fertilizing later in the season or about the first of September.
Dahlias bloom well into October, or beyond, here in Niagara. Leave the tubers in the ground until a hard frost blackens the foliage. Discard the foliage and dig up the tubers at this point. Shake off any excess soil and store the tubers in a dry, cool garage for a week or two. Clean up the tubers and pack them loosely in crates lined with newspaper; store in a cool, dry place — a wine cellar is ideal — for the winter.
Take advantage of the winter months, look up an online catalogue or two and start planning your summer garden — maybe 2019 should be the year you add dahlias to your wish list.