Dahlia

Dahlias are usually big plants, not particularly well suited to new gardeners. They have to be over-wintered indoors, they take several years to start flowering really well, and they are not low maintenance. Having said that, dahlias have much to recommend themselves. They are showy and long blooming. They make excellent cut flowers, provided that you cut them when the blooms are fully open. They don’t open very much if you cut them while they are in bud. They can live for decades, they can be easily shared with friends, and they have a rich and interesting history.

Dahlias are native to Mexico and are named for the Swedish botanist Anders Dahl, a gifted student that Linnaeus was fond of.  Although most of us call them “day-lee-uh”, the correct pronunciation is actually “doll-ee-uh”. There are 42 recognized species, but practically all that we are grow today are hybrids. As members of the daisy family and they cross-pollinate and mutate readily, leading to today’s multitudes of shapes and colours and sizes. Most of the wild forms grow about 24” tall and have single or double flowers in red, orange, yellow, or pink.

Famed for their large tubers (which are actually edible), which were occasionally used for medicinal purposes as well. When the Spaniards first arrived in the new world, they found dahlias being cultivated in Montezuma’s garden; the only plant that was cherished for its beauty above all other things.

Dahlias are not going to score any points with the modern gardener who is looking for something “low maintenance, drought resistant, and care-free.” They are none of those things. In the first place, because they are Mexican, they are very sensitive to cold and frost. Dahlias want abundant warmth, and will turn black and suffer at the first hint of frost or cold. They are also very heavy feeders, and they need to be grown in rich, fertile soil and fed regularly. They are also not drought resistant; they are big, leafy plants that drink significant amounts of water and they will not tolerate dry soil. The hollow stems mean that sometimes they need to be staked or supported, as they are prone to breaking in the wind. Hail will devastate dahlias, and they do not always recover if smashed by inclement weather.

So why bother growing dahlias? The flowers are spectacular and come in pretty much every conceivable colour except blue. They flower late in the year when the garden is needing something vibrant, they flower for weeks and weeks. They are also excellent subjects for large containers and barrels. In 1963, the dahlia was declared the national flower of Mexico. 

Let’s say that you have a warm, sunny, sheltered site with rich soil and plenty of water. Sounds like the perfect dahlia habitat, doesn’t it? Unfortunately, every single thing that likes to eat plants will eat your dahlias. Deer love them, and rabbits, grasshoppers, and caterpillars of all kinds will eat them. Squirrels will eat the new shoots. Slugs and snails can be tremendous problems and can decimate a plant overnight. Earwigs, thrips, spidermites, and cutworms also find dahlias very tasty. Dahlias will draw aphids like a magnet (if they're a problem, wash them off with the hose).

Unfortunately, they are prone to a number of viral infections and plant diseases. Botrytis, powdery mildew, and various molds and root rots can also be troublesome. It’s not unusual to have a dahlia growing and performing just fine and then suddenly lose it in the course of a weekend to one issue or another. This is the heartbreak (and reality) of dahlia growing and in spite of this, prairie gardeners have been cultivating them for decades.

Dahlias make up for their faults by being very inexpensive and widely available, and also quite easy to propagate. Tubers will grow larger every year and can easily be divided and separated. Sometimes it’s best to have several plants of a variety you like, just in case one is lost to some illness or health issue.

Seed grown dahlias are highly variable and grow quickly, flowering in a short time. You can keep the ones you like (they will form tubers) and discard the ones you don’t. They are sometimes even available as bedding plants in the little annual packs. Dahlias grown from tubers take a bit longer to get to flowering size. Any big box store will sell you a package of dahlia tubers for only a few dollars. A lot of people take these home and plant them, and if they don’t die of one of the aforementioned dahlia issues, they often don’t flower well when they are so young. This leads many gardeners to say “well, it hardly performed so why would I bother to lift and save it?” The fact is, lifting and saving your dahlias is worth it.

Dahlias require a frost-free climate in order to survive the winter, so how do you go about “lifting” them? Most serious dahlia growers on the prairies get their plants into the garden in late May or early June at the earliest. They are usually in full flower by August and September, and will sometimes flower into October if conditions suit them. This is one plant that you should be meticulous about dead-heading once it blooms.

Overwintering

After the dahlias have been leveled by frost (both stems and leaves will turn black and collapse), leave them standing in the ground for about 10 days. This helps the plant to harden off and go into its “rest” phase. Then, carefully dig up the tubers. After they are dug up, cut off the frozen top growth and carefully wash all the dirt from the tubers. Discard any that are damaged or injured. They can then go into boxes or containers of dry peat moss or coco fiber for the winter. They need to be kept cold, but definitely not freezing. Somewhere between about 5 and 10 degrees Celsius is perfect. Check on them a few times in the winter. If the tubers are shriveling, give them some water. If they are rotting or getting moldy, they are too wet! Increase air circulation and discard any infected tubers. Some people will pot them up indoors in mid March to mid April, but you can also plant them directly into the ground once the soil is thoroughly warm. The older they get, the more they will flower and the bigger the flowers will be. Dahlias can live for decades in this way and you will definitely get your money’s worth out of them!

Forms of dahlias

If you look at any catalogue or magazine that offers dahlias, you will be astounded by their diversity! There are many different groups and sub-divisions of dahlias, most of which refer to the shape and flower size. There are about 60 000 registered cultivars of dahlias, with many added every year. Categories for dahlias include:

• Single-flowered (they look like daisies)
• Anemone-flowered (kind of like the singles but with longer petals and usually the central disk being absent or unseen)
• Collared (with a central ring of florets in the center, often another colour and resembling a collar)
• waterlily (very double)
• Decorative
• Ball (self-explanatory)
• Pompon (which are hard to tell apart from ball)
• Cactus (with petals that roll inwards and create a spiky looking flower)
• Semi-cactus (partially like a cactus)
• Miscellaneous
• Dinnerplate, which are dahlias with enormous double flowers that can be up to 12” in diameter. (though probably not quite that big on the Prairies)