Growing Dahlias: 7 Must-Know Tips Before You Start

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These top tips for growing dahlias provide an excellent overview for beginners to understand how to grow these beautiful flowering tubers and provide the care they need.

When you’re ready to plant your tubers, this explains when to start dahlias indoors or outdoors.

Large pink dahlias blooming in the garden.

How to Grow Dahlias

I gathered these tips for growing dahlias from numerous sources including books, research papers, my own experience, and advice from professional growers whose livelihood depends on their success.

While methods and opinions vary, if the basic needs are met, you should do just fine.

Dahlia | Genus: Dahlia | Asteraceae family

Dahlia Growing Tips
Tuberous herbaceous perennial native to Mexico and Central America

42 species | 57k cultivars
USDA Hardiness Zone: 8 up
Grow with winter storage: zone 2 up
Sun: 6+ hours full morning sun
Soil: pH 6.5, does not like damp or dry
Start indoors: 4 to 6 weeks before last frost
Plant outdoors: after last frost, soil 60°F (16°C)
Propagation: seed, tubers, cuttings, grafting
Flowers: mid-summer through to fall frosts
Cold climates: store tubers for winter at 40-45°F (4-7°C)
Pollinators: mainly bees and beetles
Larval host plant: dahlia support various Lepidoptera, specifically moths

Shop Online: Buy Dahlia tubers (Amazon)

Top Dahlia Growing Tips
Frequently Asked Questions
Resources

Top Dahlia Growing Tips

Watch Quick Dahlia Growing Tips

1Start Your Dahlias Indoors For an Earlier Bloom Time

Dahlias take 90 to 120 days to flower after planting, depending on the variety you are growing.

Generally, the larger the plant and flowers, the longer it takes.

If you want flowers before late summer, consider starting your dahlia tubers indoors in pots 4 to 6 weeks before last frost. This head start provides a longer flowering season.

See How to Start Dahlias Indoors here.

2Tag Your Dahlias So You Know What to Expect

While dahlias are not frost hardy they are perennial and this means we can grow the same tubers year after year—if they are protected from freezing temperatures with winter storage.

But, with so many different species (42) and cultivars (57k), there are many different flower shapes, colors, and plant sizes—and different needs—and there is no way to identify them by looking at the tubers.

Tags to the rescue! By keeping track of each dahlia both through the growing season and in storage, come planting time, you’ll know what it needs and where to plant it.

See How to Tag and Track Dahlias here.

3Stake Your Dahlias at Planting Time (Not After)

The wonderful thing about dahlias is the massive flowers, of course, but they tend to be top-heavy and pretty much always require support to avoid stem damage.

Save yourself future trouble by installing the support post right at planting time. This avoids accidental puncturing of the tuber later.

With a good support post (rebar, pipe, wood) placed next to the eye of the tuber (see the planting tips below), the main stem of the dahlia will grow right where you need it.

Twine is added as the plant grows. Make a loose loop around the stem and a tight loop around the support pole to keep things in place without damaging the plant.

See more about Supporting Dahlias here.

4Don’t Be Afraid to Pinch Your Main Stem

While you can leave your dahlias to grow without any grooming, you may want to ‘pinch back’ the main stem once there are several sets of leaves.

Pinching back (the same as cutting off) the main stem encourages the plant to become bushier and put more energy into lateral shoots and additional blooms.

Alternately, growers who enter their dahlias into flower-growing competitions may remove all the lateral stems leaving the main stem to produce a single, spectacular flower.

See more on Pinching, Grooming, and Topping here.

5Grow in Containers to Discourage Slugs and Snails

If your garden tends to be a magnet for slugs or snails, consider growing your dahlias in containers. This has more tips on dealing with slugs and snails without harming your garden.

Often miniature dahlias are recommended for pots but you can certainly try growing any size dahlia this way.

In my experience, the larger the container, the better. And, with the pot off the ground, the chance of slug or snail feasts is greatly reduced.

Learn more about possible Pest and Diseases here.

6Grow Dahlias in Full Morning Sun

Dahlias are one of those plants that like their soil moisture nice and even.

If the soil holds too much moisture, the tubers, especially in the first few weeks, are prone to rot.

And, if the soil dries out, they can wither and die.

If you can, choose a location with full morning sun so they get maximum light without direct exposure to hot, drying afternoon sun.

7Store Your Tubers in Plastic Food Wrap for the Winter

Every enthusiastic dahlia grower will tell you their storage method works like a charm. And—they are right—for their specific conditions. The point is, it’s the health of the tuber and the overall environment that counts.

The optimum storage temperature is 40-45°F (4-7°C). We run into problems when the heating systems in our homes make the humidity level too low for the tubers.

If this sounds like your situation, consider using the plastic food wrap method (more on this below). Each tuber is wrapped individually to keep moisture in. Growers who use this method report a higher number of viable tubers each spring.

Read more about Winter Storage Methods here.

Frequently Asked Questions

Are dahlias perennials?

Dahlias are tuberous, herbaceous perennials native to Mexico and Central America. While they are perennial, they are not cold hardy below USDA hardiness zone 8. To avoid freezing conditions, cold climate gardeners dig them up and store them for the winter and replant them in spring.

Do dahlias come back every year?

If you are in a cold climate (below hardiness zone 8), dahlias left in the ground for the winter will not come back each year because they do not tolerate freezing conditions.

When should I plant dahlias?

To allow enough time for dahlias to flower in cold climates, you can start the tubers indoors in containers 4 to 6 weeks before last frost. Faster-growing dahlias can be planted directly outside when the risk of frost has passed and the soil temperature is consistently 60°F (16°C) or warmer. This has complete instructions for planting dahlias.

When do dahlias bloom?

Dahlias flower approximately 3-4 months after planting. The larger the variety, the longer it takes.

How can I keep slugs and snails off my dahlias?

You can avoid damage from slugs or snails by growing dahlias in containers. Keep the containers off the ground to limit access.

Can I leave dahlias in the ground over winter?

Most cold climate gardeners dig up their dahlias in fall and store them for the winter to avoid damage from freezing conditions. If winter conditions stay around freezing or warmer, it is possible to insulate the garden bed with several inches of straw to prevent damage and keep the tubers in the ground.

How do you winterize dahlias?

Winterizing dahlias requires several steps. Dig them up. Clean them up, removing stems, flowers, and any dead parts. Air dry the tubers for several days. Then wrap in clear, plastic food wrap and store them in a cool, dark place between 40-45°F (4-7°C) with medium to high humidity. This has complete instructions for overwintering dahlias.