5 Places You Should Never Plant Dahlias, According to Gardening Experts

Dahlias are beautiful flowers that put on a real show in the warmer months. However, while dahlias are forgiving blooms and easy enough to grow, there are certain parts of the garden where you should never plant them.

If you grow dahlias in the right spot and care for them properly, you'll be rewarded with a vibrant display of yellow, white, and pink blooms that look just as beautiful in a bouquet as in your garden. To help you start this dahlia journey on the right foot, we spoke to experts about where you should always avoid planting them.

Small Pots

Dahlias can indeed be grown in containers, but not if said containers are too small.

"In a pot that's less than 12 inches deep and wide, the plant will have stunted growth and poor flowering," says Kate Walz, owner of KW Gardens and Flowers. "The roots will become cramped, and there's less soil and nutrients to produce flowers."

Instead, Mary Turner, the owner of Salt Farm Flowers, recommends growing dahlias in a pot that's at least 15 inches across. Otherwise, not only will your flowers be weak and spindly, but they can also cause the container to tip over and break since these plants are so top-heavy.

Soggy Soil

Dahlias do best in loose, well-drained soil, so anything that's too damp, clay-based, or soggy is a no-go. Walz notes that they're "kind of like potatoes, in that they are fleshy, starchy storage organs," and therefore don't fare well when exposed to excess moisture.

"Any place that has standing water is too wet," says Turner. "The dahlia tuber will rot. If you have no other choice, make a raised bed to plant them in."

Hot, Humid Climates

Dahlias need full sun to thrive—ideally six to eight hours a day—but very hot temperatures can be a real problem. Walz notes that when daytime temperatures are above 90 degrees Fahrenheit and evening temperatures are above 70 to 80 degrees Fahrenheit, the plant will struggle to survive.

"They won't have a chance to rest and reset metabolically, which they need to produce abundant blooms," she says. Instead, Turner adds, they will look "green and beautiful ... but they won't produce any flowers."

Walz notes that in her Zone 7 garden, the dahlias really shine in September when the soil is warm but the nights have cooled, giving the plant time to put all its energy into bud formation and bloom production.

Shady Spots

Since dahlias do best in full sun, shady areas of the garden are less than ideal.

"Putting them in deep shade or a densely wooded area will cause them to become leggy as they reach for the light," says Walz. "They will rarely flower, since dahlias need sun to fuel the energy-intensive process of blooming."

Close to Other Flowers

Dahlias need their space! That includes space away from other plants—and other dahlias.

"They need at least 18 inches of spacing at minimum to grow," says Turner. "Giving them more space allows them to be less stressed and less prone to diseases and insects."