4 Dahlia Growing Mistakes You Might Be Making—and How to Fix Them

Dahlias are having a moment, with more and more gardeners embracing them for their eye-popping summer blooms. But a few growing missteps can result in fewer flowers and even destroy your plants, says Julie Williams, co-owner of Stonehouse Dahlias and dahlia grower for more than 20 years. Here, she shares the most common mistakes gardeners tend to make with dahlias—and how to fix them right now.

Mistake 1: Keeping Them Indoors Too Long

Many gardeners like to get a jump on summer by planting a dahlia in a pot indoors, then transplanting it into the garden. But don't wait too long to do this, warns Williams. "Most windowsills don’t provide dahlias with enough sunlight, which can lead to a weak, lanky plant," she says.

The Fix: The best time to transplant your dahlia from indoor pot to outdoor bed is as soon as a chance of frost has passed. But if you've missed that window, no worries: "If your plant has already started to stretch from being indoors too long, plant it very deep, burying some leaf nodes," says Williams. "Every buried leaf node will send out roots to nourish and strengthen the plant."

Mistake 2: Watering All Dahlias the Same Way

Dahlias can be grown either from tubers or from cuttings. But the two types of plants have different watering needs—which can be a problem if you're watering them all in the same bed, in the same way. "Overwatered tubers are prone to rot, while underwatered cuttings will dry and wither," says Williams.

The Fix: If space allows, keep your tubers and cuttings in separate areas. Hold off on watering tubers until you see growth above the soil. Dahlias grown from cuttings should be watered often for the first couple of weeks; unlike tubers, they will also benefit from fertilizer for nutrients.

Mistake 3: Not Cutting Back Dahlias

It may seem counterintuitive to interfere with a dahlia's natural growth. But "left on their own, dahlia plants tend to grow tall and skinny without many branches or blossoms," says Williams.

The Fix: As soon as a plant reaches around a foot tall, clip it just above the top set of leaves—a process called topping. Even if you've missed this window and your plant is already a little taller, it's not too late. "Removing this central shoot encourages the plant to branch," explains Williams. "Rather than just a single growth point, the plant will now send out many side shoots, which will all produce flowers."

Mistake 4: Not Staking Dahlias

When dahlias are just wee sprouts, it's hard to imagine the heights they'll reach, especially if you're new to growing them. But failing to stake dahlias can result in floppy plants, and worse. "Dahlias are brittle and can break or tip over in a strong wind," says Williams. "Many growers lose their beloved dahlias during wind storms."

The Fix: Even if your dahlia has already grown a couple feet tall, there's still time to stake it. Place a sturdy stake close to the plant, using twine to tie it to the stem every foot or two, suggest Williams. (If you've grown a dahlia from a tuber, make sure not to place the stake so close you impale the tuber.) Another option? Pop a tomato cage over the plant, she says.