Tips From the Dahlia Master

The Nature of Dahlias

Dahlias are grown from tubers which are commonly confused with blubs. Tubers are more like a potato with a thin skin and they sprout eyes while blubs have layers and layers of thin skin for protection. The delicate tuber needs more coddling to keep it away from excess moisture and freezing ground temperatures. If they sit in saturated wet soil, they will rot, which is why they are dug up every year and protected during the winter (there are some exceptions explained below).

When to Plant and Harvest Dahlias

The time to plant dahlias is after the last frost in your gardening zone when the ground temperatures are warm enough. I plant tubers at High Hampton Resort beginning around Mother’s Day through Memorial Day. We are harvesting the majority of flowers 60 to 75 days after planting, which is around the middle of July. The garden is at full peak throughout August and the first couple of weeks of September. Then in mid-October, when we start to lose sunlight, it’s time to dig them up before the first freeze and the rainy season.

Where to Plant Dahlias

Dahlias need a minimum of six hours of sunlight and good breezes and cross ventilation. The secret sauce in Cashiers is our cool nights, which make it an ideal home for dahlias. If you live in the deep south where the nights are warm, dahlias are a little trickier to grow because they don’t have time to recuperate from the heat; they may look tired and wilted.  You can experiment by growing dahlias in containers in various sunny spots on your property to find the location where they thrive the best.

How to Plant Dahlias

I generally recommend planting the tubers 18 to 20 inches apart. Sometime you can get away with 12 inches if you want a mass of a particular varietal. I dig a six to eight–inch hole and add some nutrients such as organic bone meal in the dig site.

Stake them at the time of planting; you know where the tuber is and if you blind stake later, you risk puncturing the tuber. I also recommend using a very sturdy stake; avoid the thin bamboo ones and opt for the solid tomato stakes and put about one foot of a six-foot stake in the ground. Since the plants can grow over four feet, they need to be properly supported and tied off when they begin to grow. In Cashiers, we have plenty of rainfall, so no irrigation system is required. I will sometimes hand water if needed.

Digging and Storing Dahlia Tubers

Dahlia tubers are very delicate, so you need to take time and care so you don’t puncture or split the tubers during the digging process. After digging them up, I clean them in a light disinfectant in case they have any fungus or bacteria on them; then put them in crates and store in a cool dark basement on the property until time for planting. You don’t want the temperature to be higher than 55 degrees or they may sprout prematurely, and you don’t want the temps to drop below freezing; you want the tubers to stay dormant. You also need to have good airflow and correct humidity; if the air is too humid, the tubers will start to rot; not enough and they will shrivel up like raisins!

Overwintering Dahlias

People often ask, “Do I have to dig up dahlia tubers?” With the warming climates throughout the Southeast, we don’t have many more three-to-four-week-long freezes, so it’s becoming more and more popular to leave the tubers in the ground over the winter months. I have been experimenting in my own garden and a few gardens that I manage. First, I cover the tubers with thick trash bags and then do some heavy mulching during the fall to protect and insulate them and keep undue moisture at bay. It really is trial and error though. You have to get the trash bags off before it gets too warm. One year, I waited too long and discovered two feet of stem coiled up underneath! I experiment with different techniques every season; not using trash bags and minimal mulching, etc. Rest assured though that I will always dig up the dahlias at High Hampton Resort—I won’t take any chances with them!