With a little foresight it is possible to enjoy dahlias in our southern gardens during our hot, humid summers—the key word here is “foresight.” Ideally, this Mexican native wants cool nights and warm days, something California with its Mediterranean climate can provide but which we cannot.
Today there are over 50,000 named cultivars—some dahlia aficionados call them varieties—and most of them are inappropriate additions to our gardens. But do not despair as you can add these beauties to your garden. However, there are several things you must do:
• Plant the right variety. Fortunately there is a wonderful resource on the Internet for the southern would-be dahlia grower: www.dahilasocietyofgeorgia.com. This website list all the varieties that can grow in the South. Some varieties can tolerate our heat and humidity better than others and this knowledgeable website has done all the work for you in choosing which dahlia you should grow. The ‘Bishop of Llandaff’ does well here, along with ‘Lavender Perfection’ and ‘Urchin’.
• Now is the perfect time to plant dahlias, which want a warm soil around 70 degrees F. The rule of thumb is to plant dahlias when it’s time to plant tomatoes.
• Dahlias range from 3-7 feet (not including Dahlia imperialis, the giant tree dahlia) and keep in mind that tall dahlias require staking. If you are planting a tall variety, include the stakes at planting time as adding them later can potentially harm the tubers.
• A well-draining soil is necessary if you want to grow dahlias. They do not tolerate un-amended clay soils, which promote tuber rot—something you don’t want.
• Dahlias need at least six hours of sun—preferably more morning sun than late afternoon sun.
• After planting the tubers in warm well-draining soil in a sunny location, do not water until the plants are 4-6 inches high; to do so risks tuber rot.
• Dahlias prefer a pH of 6.5. If you don’t know what your pH reading is, get a soil test.
• Dahlias appreciate drinks of water when the soil is dry. The soil should dry between waterings.
• To promote blooms deadhead your dahlias.
• As for deer, some deer eat dahlias while others do not. My deer leave them alone, but there is no guarantee, alas.
Do not despair if your dahlias bloom sparsely during the heat of the summer. As soon as the nights begin to cool dahlias begin to perk up, putting forth never-ending blooms. They appreciate a foliar feeding occasionally but avoid late applications of fertilizer, which can promote tuber rot.
Experts will tell you in our Zone 7 we have to dig up the tubers in the fall; the Dahlia Society of Georgia, however, recommends leaving the tubers in the ground while heavily mulching them before winter settles in.
This may sound like a lot of work but, once established, dahlias in our southern gardens are undemanding creatures, disappearing in the late fall and poking their heads up when the warm soil tells them it is safe to do so. What more can you ask of a plant?
Featured image – Dahlia ‘Bishop of Llandaff’-by JC Raulston Arboretum
A serious gardener for the past twenty years, Kit Flynn resides in Chapel Hill. She is also a Durham Master Gardener and a member of the Durham Garden Forum Advisory Committee.