Dahlias are booming in popularity, especially with a resurgence of interest in old-fashioned flowers like your grandma grew. “Dahlias come in so many beautiful varieties, from short 8-inch-tall plants to those with dinner plate-sized flowers,” says dahlia grower Andy Hunter of Lynch Creek Dahlias. “They have tons of long-lasting blooms that go from mid-summer to the first frost, and they last a long time in the vase so they’re great in cutting gardens.”
Dahlias are planted as tubers that sort of resemble skinny sweet potatoes. In warm climates such as USDA Hardiness Zones 8 and warmer (find your zone here), they are perennials and can stay in the ground year-round. In cold climates, you can dig them up after the first killing frost or two and save the tubers for planting again next spring.
“There are some varieties you can keep going for decades,” says Hunter.
They’re also incredibly diverse with forms and colors for every type of flower lover. Flower shapes include everything from cute pom-pom balls to cactus-style flowers to big, lush blooms. The colors are nearly endless, ranging from hot pink to pure white to deepest burgundy and everything in between. Pollinators also love them!
But if you’ve ever wondered why your dahlias don’t seem to bloom like you expected, with few (or no!) flowers, you’re not alone. It’s a common problem that often affects home growers, but you can fix it, says Hunter.
The Number One Reason Dahlias Don’t Bloom Well
The most common reason dahlias don’t do well is improper watering. “Dahlias need a good soaking, not a surface watering,” says Hunter. “Yet they also don’t want to have soggy feet, which causes the tuber to rot in the ground.”
Good watering habits start from the moment you plant the tubers. After planting, don’t water them—though it’s fine if it rains. “The tubers contain plenty of moisture to get started,” says Hunter. Let the plants push up some foliage first before you start watering—even as much as letting the plant get a foot tall or to its third set of leaves before you start regular watering.
These flowers want a deep watering, then they should be allowed to dry out. “I prefer drip irrigation about three times a week so it gets down about 6 inches deep,” says Hunter. You may need to do so more or less often depending on your soil type, so poke your finger in and get a sense of the moisture level after watering so you get a feel for it.
If you’re hand-watering with the hose, water one plant for 10 seconds, then let it soak in as you water the next plant in line, going down the line and watering each plant for 10-second intervals. Come back to the beginning of the line and start the process again. This allows the water to soak in, rather than running off the surface, says Hunter.
Another Reason Dahlias Don’t Bloom Well
If your dahlias have been in the ground for several years, there’s another reason they don’t bloom well after a few seasons. “They get crowded, and there’s too much competition so there are lots of leaves but no flowers,” says Hunter.
Typically, this means your dahlias need to be divided. You’ll probably need to do so every two to three years, preferably in the fall. But the good news is that dividing means you’ll be able to harvest more dahlia tubers to plant elsewhere in your garden or to share with friends, says Hunter.
