I get asked this question every single spring: Are dahlias annuals or perennials? The short answer is that they are tender perennials. However, how you treat them in your backyard entirely depends on your local climate.
If you live in USDA Hardiness Zones 8 through 11, you can leave dahlia tubers in the ground all winter, and they will reliably come back year after year like any other perennial plant. But for those of us gardening in Zone 7 and below, the freezing winter soil will turn those fleshy tubers to mush. In colder climates, we have to treat them as annuals—or put in a little elbow grease to dig them up and store them indoors over the winter.
Dahlias have been a staple in my garden for years. There is simply no other flower that gives you such a relentless, high-impact explosion of color from mid-summer right up until the first frost. Whether you are planting them in a dedicated cutting garden or mixing them into an acid-loving border, here is exactly how to handle these showstoppers.
- ❄️ Know Your Zone: Zones 8-11 can leave tubers in the ground. Zones 7 and below must dig them up before the ground freezes.
- ☀️ Full Sun is Non-Negotiable: Dahlias need at least 6 to 8 hours of direct sunlight daily to produce those massive, heavy blooms.
- ✂️ Pinch for Bushier Plants: When the plant is about a foot tall, pinch out the center shoot. It feels harsh, but it forces the plant to branch out and produce double the flowers.
- 💧 Don’t Water at Planting: Plant your tubers in slightly moist soil, but do not water them again until you see the first green shoots break the surface. Overwatering early causes tuber rot.
Starting Dahlias: Tubers vs. Seeds
Most serious growers start dahlias from dormant tubers. Buying tubers early in the spring means you get the pick of this season’s freshest stock. Always ensure the tubers you buy are sound, firm, and not shriveled; they should feel a bit like a slightly wrinkled potato, ready to grow.
However, for the more enterprising gardener, there is the challenge of growing them from seed. Strains like ‘Bishop’s Children’ produce exotic, dark-leaved plants with vivid, jewel-like flowers in searing reds and scintillating oranges. I was once given a couple of seedheads of Dahlia coccinea—a species with single flowers of unremitting red. I sprinkled them on seed compost, and they all germinated, bloomed, and even produced saveable tubers in their very first year!
Planting and Summer Care
Dahlias originally come from Mexico, which tells you everything you need to know about what they like: heat and sun. In years of soaring temperatures, they give a virtuoso performance, relishing the heat of July and August.
You can pot tubers indoors in March to get a head start, using a peat-free compost. Keep the crown level with the soil surface. Once the shoots emerge, nip out the growing tips to encourage a bushy habit. If you decide to plant tubers straight into the garden, wait until all danger of frost has completely passed and the soil has warmed up.
Dig a hole about 4 to 6 inches deep, lay the tuber horizontally with the “eye” pointing up, and cover it. Stake the heavy-blooming varieties immediately at planting time—if you try to drive a stake into the ground later in the summer, you risk piercing the underground tubers.
The Secret to Endless Blooms
Dahlias are heavy feeders. To maintain flower quality and continuous production, water them deeply once a week and apply a high-potash liquid fertilizer (like a standard tomato feed) every two weeks once the first buds appear. Most importantly: deadhead relentlessly! The moment a flower starts to fade, cut it deep down the stem to signal the plant to produce more buds.
Post-Bloom Care: The Art of Overwintering
If you live in a cold climate, overwintering them requires a strict routine. After the first hard frost blackens the foliage, cut the main stems back to about 4 inches above the ground. Leave them in the soil for another week to allow the “eyes” for next year to fully develop.
Carefully dig right under the root mass with a garden fork. Shake off the excess soil and invert the tubers on a shelf in a dry shed or garage for a few days so the hollow stems can drain completely. If water sits inside those cut stems, the tuber will rot from the inside out.
Once you are certain they have dried out properly, pack them in breathable containers filled with wood shavings, peat moss, or dry shredded paper. Store them in a cool, dark, frost-free place (around 45°F to 50°F is ideal). Check on them once a month during winter. If they look too shriveled, give the packing material a very light mist of water.
Final Checklist for Success
Before you get your hands dirty, here is a quick summary of my routine for handling dahlia tubers:
- When buying packaged tubers from a garden center, soak them in a bowl of tepid water for an hour before planting to recharge any wizened roots.
- Pot them singly using a high-quality, free-draining potting mix.
- Ensure the base of last year’s stalk is buried just below the surface, as this is exactly where the new young shoots will emerge.
- Keep the pots in a warm, sunny window. Give them a light mist daily with tepid water until green shoots appear.
- Once the weather is reliably warm, transplant them into the garden, stand back, and watch the spectacular show unfold!
Read next: The Best Snow Shovels to Survive the Winter
Comments are closed.