Can Dahlias Thrive in the Deep South and Other Hot Spots?
Five of Our Customers Say Yes!

        Dahlias, it’s generally agreed, like it cool. They’re native to high mountain plateaus in Mexico where the days are warm but nights are cool, they bloom exuberantly in the fall, and they’re great favorites in northern states like Minnesota. So for years we’ve been warning Deep South gardeners away from dahlias. But our customers are constantly teaching us (thanks!), and here’s what five of them who garden in zones 8 and 9 South have to say about succeeding with dahlias where summers are HOT.

Georgia Dahlia Expert Offers Tips for Success

        John Kreiner of the Dahlia Society of Georgia has been growing dahlias in the Deep South for 31 years. He planted his first ones in zone-8b San Antonio way back when, and today he gardens in zone-8a Atlanta. Here’s his simple but important advice:

        “There are a lot of things that we in the South must do to be successful in growing dahlias but the two most important in my opinion are:

“1. MULCH them.
        “To keep dahlias alive through the heat of summer so we can enjoy the blooms that come when temperatures cool in the fall, mulching is a must. The sensitive feeder roots of dahlias grow just under the soil surface and can extend for up to two feet in all directions. To keep them cool, cover the soil with at least 2 inches of a good mulch that will let water through easily – and be sure to do it before July 1! Very light afternoon shade can be a help, too.”

“2. Even more important, grow dahlias that are HEAT TOLERANT.
        “We learn this by growing them. The ones Old House Gardens offers that I know will grow well in the South are:

‘Kidd’s Climax’

        We asked John to trial a few of our hard-to-find favorites last summer, and three did so well he added them to his heat tolerant list:
        ‘Prince Noir’ – “This dahlia is the best of those you sent me. It was the second to bloom of all the dahlias in my garden, so it is an early bloomer. It had lovely, dark, maroon-red blooms that have been enjoyed by everyone who has seen them. It bloomed all summer and has grown very well. It put out plenty of laterals and lots of blooms and was a very nice addition to my garden. I highly recommend it as a heat-tolerant dahlia.”

‘Prince Noir’

        In zones 8-11 you can leave your dahlias in the ground all winter, but John says they will grow and bloom best if you dig and divide the tubers every 2-3 years anyway. Most growers cut the stalks down at some point, and John recommends capping each with a bit of tin foil and a rubber band so water doesn’t collect in them and rot the crown and next year’s sprouts. He also adds 4-6 inches of mulch directly over the tubers for their winter rest.

Misting on the Hottest Days Can Help, Too

        Even here in our zone-6 Michigan garden we’ve taken a tip from American Dahlia Society members in the Southeast who mist their dahlias on particularly hot, sunny afternoons. The evaporating mist helps to cool the plants and keep them thriving. Our misting techniques here are very low-tech. Basically we just spray them with our watering wand.

Success Stories from South Carolina, Texas, and Arizona

        You don’t have to be an expert like John to grow dahlias where summers are blazing hot. Here’s what four of our customers who are ordinary, backyard gardeners in zones 8-9S told us about their successes. (If you’ve had success with dahlias in zones 8-9S, too, please email us your story. We’re always eager to learn!)

        Val Myers of zone-8 Georgetown, SC, 60 miles north of Charleston, wrote us in July of 2006: “Last year I purchased ‘Claire de Lune’ and ‘Union Jack’. ‘Clair’ performed well its first year but ‘Jack’ was slow to start. This year, however, ‘Union Jack’ has not only returned but gone berserk. It has spread to about three feet wide and high and is fighting tooth and nail with gaura for space in my planter. It began blooming at least a month ago and is still trying even in the 90 degree heat with 90% humidity. It’s in a large planter filled with great soil and gets filtered shade most of the day with direct sun only late in the afternoon. It’s irrigated via a drip line and heavily mulched to prevent water loss.”

‘Claire de Lune’

        Kathryn Chauveaux of zone-9 Beaumont, Texas, on the Gulf Coast writes: “Dahlias thrive for me here. They seem to love the heat and humidity, and the more you cut them the more they bloom. I plant pompons just because I like their shape. They’re on the south side of my house in full sun, between my azaleas and wall of the house [OHG: This is a location we would never recommend, but . . . .] The soil is rich with organic matter and slightly acidic. I usually plant them in late May to avoid our sometimes heavy spring rains. I dig a hole 4-6 inches deep and sometimes add a little bulb food covered with a layer of sand. Then I put in a stake and fill up the hole. I add Super Thrive to the first watering and then wait for some green to show before I water again. When they bloom, I cut them for bouquets which stimulates more blooms. And that’s about it. Once planted, they are basically on their own.”

        Della Smith is the proud grandmother of a thriving Houston dahlia. She writes: “One of your ‘Bishop of Landaffs’ is alive and well in zone-9 Houston, Texas! My daughter, who is a Master Gardener there, has had it return for three years now. She just leaves it in the ground over the winter and in the spring it pops back up. I was there last July, sweat box city, and it was gorgeous. I think that drainage is one of the keys for success there. It is planted in a raised bed.”

        And Mary Peace Douglas who gardens in zone-8 Tucson, Arizona, writes: “June in Arizona is called ‘the death month.’ Hot, dry, windy, and waiting for the rains. Your single dahlias, though, are thriving. Pink ‘Bonne Esperance’ is in bloom and yellow ‘Clair de Lune’ will start next week. I know dahlias are native to the mountains of Mexico so should do well here but it is always a surprise to have a plant in such good form in June.” Though the higher elevations of Sonoita and Tucson provide the cooler nights that dahlias love, still it’s clear: by choosing the right varieties and keeping them cool, gardeners in zones 8 and 9 of the South and Southwest can enjoy fabulous dahlias.