On any afternoon that I was toiling in the front border, I could count on my neighbor pausing on her daily walk. We passed the time in flower talk while her sweet, old spaniel rolled on his back in the grass, or balefully eyed a squirrel sitting on the fence. She especially loved dahlias, thrilled by their many color combinations and flower forms. She moved away a few years ago, and I miss those impromptu conversations.
She’d be happy to know that 2019 is the National Garden Bureau’s “Year of the Dahlia.”
When it comes to planting dahlias, no truer words were ever written than those by garden writer Henry Mitchell: “There is nothing like the first hot days of spring when the gardener stops wondering if it’s too soon to plant the dahlias and starts wondering if it’s too late.”
Most gardeners like to plant dahlias at the same time they do their tomatoes. I’ve gone as late as mid-June and still been rewarded with gorgeous blooms as summer spirals into fall.
Choose a well-drained location in part to full sun. Plant tubers with crowns facing up — check for signs of the original stalk (a stub sometimes is still attached to the tuber), or look for new growth. The crown should be just above soil level when planted. You’ll also find dahlias in pots, which are easily transplanted into the garden or a container.
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Dahlias usually need staking, especially dinner plate-sized and cactus forms. I use bamboo lengths and plastic rebar rods, poking them in the ground at the same time I’m planting tubers. If I wait until the flowers actually need buttressing, it’s a sure bet I’ll stab a tuber, or the stems will break as I’m trying to wrestle them inside stakes and strings. If you prefer, tomato cages work fine; remember to anchor them into the soil to prevent tipping over.
Don’t overdo with the watering wand. Give the tubers a good drink after planting, and then ignore them for a while. They don’t like overwatering. If we have an inch of rain per week, dahlias call it good. If it gets hot and dry, give them a soaking. In spring, dahlias benefit from a high nitrogen fertilizer, but switch to fertilizer with higher phosphorus and potassium in mid-season. Stop fertilizing in late August.
Here’s some dahlia genealogy from the National Garden Bureau: Native dahlias from the mountains of Mexico and Guatemala are the genetic sources for modern hybrid dahlias. Botanists who traveled with Spanish conquistadors discovered the New World plant, but it took 200 years before dahlia seeds, roots and plants arrived in Spain and other parts of Europe.
The Madrid Botanical Gardens named the genus for Andreas Dahl, a Swedish botanist. Initially breeders were interested in dahlias for food, not flowers. In 1872, a box of dahlia roots sent from Mexico arrived in Holland with only one survivor. It produced a brilliant red flower with rolled-back, pointed petals. Breeders were off to the races creating ornamental dahlias. Today’s hybrids are the offspring of these earlier varieties.
Japanese beetles like dining on the blooms, and insects like earwigs, thrips and aphids find them appealing. Meet the beetles with a soapy bucket of water, and use insecticidal soup to discourage other bothersome insects.