How to Grow Delightful Dahlias: A Late Summer Standard

Dahlia spp.

When the late season garden starts to fade from summer’s heat, dahlias are one of the best choices to add delightful months-long displays of brilliantly colored blooms.

The timing of these flowers is perfect!

From July until the arrival of frosty temperatures, these bold blossoms give a fresh look to tired beds, containers, and window boxes.

Dahlias are fast growing, and easy to cultivate and multiply as well.

Tender perennial tubers, they’re most often grown as annuals – the tubers may be lifted and stored in fall, then divided and replanted the next spring.

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And they make gorgeous cut flowers as well, with many folks growing them for the sole purpose of cutting.

The bright, showy booms have fantastic forms and fascinating geometry, adding long-lasting allure to floral arrangements.

Join us now for a look at how to grow dahlias for delightful late season color.

Here’s what’s ahead:

Dahlia is a genus of herbaceous perennials, tubers grown often as annual flowers in many regions for their brightly colored blooms in the late season garden.

Tubers are the plants’ energy storage depots. They grow large and plump over the growing season to supply the fuel needed to survive the winter months.

Native to mountainous regions of Mexico and Central America, this member of the Asteraceae family is noted for its brilliant, colorful flowers, blooming at a time when many plants are lagging and past their best.

With a long season, dahlias bloom from July right into autumn, flowering until they are killed off by frost.

The national flower of Mexico, bloom sizes can be small, like the two-inch patio varieties, while larger types like dinnerplate dahlias can have flowers as big as 14 inches across.

With over 40 species and 50,000 registered cultivars worldwide, the selection is mind-boggling.

Learn more about the different types of dahlias and their classification.

Dahlias were first cultivated by the Aztec people, who grew the tubers for eating like potatoes, and for medicinal purposes.

Large flowers and the hollow stems of tree dahlias were also used to collect and carry precious water.

They were first chronicled under the name acocotli (water pipe flower) by Spanish botanist Francisco Hernandez in 1570.

It’s unclear which plants were initially grown in North America, but the first American Dahlia Society was organized in San Francisco in 1915 – a sure sign of their growing popularity with the home gardener.

Dahlias are wonderfully versatile in the garden.

Taller varieties add attractive interest to the rear or center of beds, and mix well with other late flowering perennials and ornamental grasses.

And all varieties make a welcome addition to butterfly, cutting, and cottage gardens.

How to Grow

Tender perennials, dahlias are hardy in Zones 8 to 11. They like warm daytime temperatures of 70 to 80°F and cool evenings around 65°F.

In excessive heat and humidity, they tend to wilt and are prone to powdery mildew.

Typically grown as annuals, the tubers are lifted in autumn, stored over winter, then planted again in spring when soil temperatures have warmed to 55 to 60°F.

They need a location that receives six to eight hours of sunlight each day, preferably with some afternoon shade, in well-draining, humus-rich soil with a pH of 6.6 to 7.0.

Dahlia tubers enjoy a mounded planting site of rows or domes four to six inches tall and wide.

Mounding provides warmer soil and improves drainage. Plus, the loose, friable soil makes it easier for the new tubers to grow.

Here’s how to plant:

1. At your planting site, amend the soil with a shovelful or two of organic matter such as aged compost or well-rotted manure.
2. Add in a shovelful of landscape sand or pea gravel to improve drainage if needed.
3. Mix in bone meal for strong root development.
4. Mound the soil into rows or domes four to six inches tall and wide.
5. Plant tubers so the crown of each is under two inches of soil, eyes pointed up. If no eyes are evident, plant with tubers on the bottom and the crown on top.
6. Gently firm the soil in place.

Avoid watering at the time of planting unless conditions are very dry – overly wet conditions can cause tubers to rot, and regular springtime precipitation should be adequate.

Wait until the first leaves break through the soil before watering, then give them a good, deep soak one to three times per week as needed.

Allow the top inch of soil to dry out between watering, but for consistent growth, ensure the roots stay moist.

Find more tips on how to water dahlias here.

Add a two to three-inch layer of leaf or straw mulch for moisture retention if needed.

Dahlias are fairly heavy feeders, and a low-nitrogen fertilizer of 5-10-10 (NPK) can be applied one month after planting, and once or twice more at 30-day intervals.

Maintenance

To promote a compact shape with more flowers, pinch out the main stem early in the growing season. Pinch the larger-flowered varieties just above the third set of full leaves.

For small-flowered varieties, allow plants to reach 12 to 18 inches high, then pinch above the fourth or fifth full set of leaves.

Plants with large flowers can become top heavy and may require staking. We provide staking and support tips here.

In autumn after a hard frost, lift, clean, and store tubers for winter. Or lift by mid-November if you don’t get frosty temperatures.

Tubers can overwinter in the ground in areas with mild winters, but flowering is much more abundant when they’re lifted and divided annually.

For more details on this step, read our article on how to lift dahlias for winter storage.

Left in the ground, tubers can form a massive clump, producing more and more stems with progressively smaller and fewer flowers – until the clump eventually stops growing.

However, the annual lifting and division of tubers keeps plants strong and healthy, produces more flowers, and makes it easy to propagate new plants.

Cultivars to Select

There are 42 species and over 57,000 dahlia cultivars, with D. coccinea the parent of all hybridized plants.

Here are a few favorites from the many available cultivars:

Blue Bell

‘Blue Bell’ is a decorative type with soft pink to dark purple blooms that shimmer in the late season garden.

‘Blue Bell’

Growing up to 36 inches tall, the four-inch flowers are ideal as cut flowers and for creating colorful borders either alone or paired with yellows and pinks.

You can find packets of two, four, or eight tubers available from Eden Brothers.

Brown Sugar

With coppery-rust colored blooms, ‘Brown Sugar’ is a decorative type with four-inch blooms atop 26- to 38-inch plants.

‘Brown Sugar’

The orangey-reddish-brown petals are lighter on the outside becoming darker towards the center for a gorgeous, two-toned, earthy feel.

You can pick up tubers at Eden Brothers in packets of two, four, or eight.

Cafe au Lait

‘Cafe au Lait’ is a standout dinnerplate type with creamy-pinkish-beige flowers held atop sturdy, 48-inch stems.

‘Cafe au Lait’

The huge blooms can reach up to 10 inches across for a stunning addition to beds and borders, as well as for cut flower arrangements.

You can find ‘Cafe au Lait’ available at Eden Brothers in packets of two, four, or eight tubers.

Summer Tango Collection

A mixture of ball flowers, the Summer Tango collection adds fiery heat to the garden with four-inch globes in glorious shades of burgundy, peachy orange, and purple while the mid-green foliage adds a cooler base.

Summer Tango

Plants grow up to 40 inches and are superb as cut flowers or in mixed perennial beds, foundations, and butterfly or cottage gardens.

Tubers are available at Burpee.

Totally Tangerine

A prolific bloomer, ‘Totally Tangerine’ is an anemone-flowered type with bright pink petals surrounding a dark orange pincushion center.

Plants grow up to 36 inches tall and the blooms are four inches wide.

‘Totally Tangerine’

This one is an excellent addition to beds, borders, or patio pots, providing texture as well as color.

You can find packets of two, four, or eight tubers available at Eden Brothers.

Propagation

Dahlias can be propagated by cuttings, tuber division, or seed. However, growing plants from seed is an unreliable method.

Most of the stock available for home gardens comes from hybrid cultivars, which may produce offspring untrue to the parents.

Cuttings

Cuttings are clones of the mother plant, so they always produce the same qualities.

Sprout cuttings can produce up to six new plants from a single tuber, but they require a controlled environment of consistent humidity, warm temperatures, and day length.

Dahlias are photosensitive, and to develop healthy feeder roots as well as tubers, they require a day length of 12 hours or greater. If needed, add a grow light to your setup to meet this rooting requirement. 

In late winter or early spring, choose a selection of healthy, firm tubers from your storage bin.

Add four to six inches of moist potting soil to a tray – or create your own soil blend of one half aged compost and one half landscape sand.

Nestle tubers into the soil, covering the bottom two-thirds, but keeping the neck and crown above the soil.

Place the tray in a 65 to 75°F location where it can receive bright indirect light.

Keep the soil moist but not wet, and within three to four weeks, sprouts will emerge from the tubers.

Once the sprouts are three inches or taller, use a clean, sharp knife to carefully cut each sprout away, taking a small notch of tuber with it.

Remove the bottom set of leaves and dip the lower one to two inches of stem into a rooting compound, then gently shake off the excess.

Fill small, four- to six-inch pots with moist potting soil.

Make holes and insert three stems into each pot, one to two inches deep, and gently firm the soil around each stem.

Maintain even moisture in the potting medium, but do not allow it to become waterlogged.

Place in a 65 to 75°F location that receives bright, indirect light for at least 12 hours each day. Roots form in two to three weeks.

Eight to 10 weeks later, sprout cuttings can be transplanted to larger pots, or planted into the garden when soil temperatures warm to 55 to 60°F.

Tuber Division

Tuber division is a simple propagation method and divisions also produce clone offspring with the same characteristics as the mother plant.

For successful propagation, it’s important that each division has a section of crown with a healthy neck and piece of tuber attached.

When all danger of frost has passed, remove tubers from storage and gently brush away any storage material.

Use a clean, sharp garden knife or shears to carefully dissect the crown.

First cut the crown in half, then cut again equally into quarters or thirds; aim to have a piece of crown at least the size of a marble for each new division.

Allow the divisions to air dry for 24 to 36 hours before planting out into containers or the garden.

Get more details on dividing dahlias or learn how to propagate them via stem cuttings.

Pests and Disease

Dahlias are resistant to deer and squirrels, but slugs and snails enjoy munching on tender new growth when young leaves and stems emerge from the soil.

Hand pick and dispose of slugs and snails, or control their access with a barrier of diatomaceous earth.

If these slimy gastropods are problematic for you, be sure to read our article on the best natural methods to protect your garden from slugs and snails.

Pests

Caterpillars like to chew on the foliage as well, and can also be controlled by hand picking.

Other pests include sap suckers such as aphids, spider mites, and thrips.

These pests can weaken plants, spread viruses such as necrotic spot, and cause black spots on leaves and buds, yellowing leaves, and distorted or stunted growth.

Control sap suckers with the addition of beneficial insects such as ladybugs and lacewings.

Or a strong blast of water from the garden hose is effective as well – be sure to spray the top of leaves, undersides, and stems.

For persistent infestations, an application of a residue-free insecticidal soap may be necessary.

Bonide Insecticidal Soap

Bonide Insecticidal Soap is recommended for organic gardens and is available at Arbico Organics.

Learn more about identifying and controlling dahlia pests.

Disease

Common diseases include gray mold or Botrytis blight, caused by Botrytis cinerea, and powdery mildew, caused by Golovinomyces cichoracearum.

Gray mold appears as a fuzzy, light gray growth after extended periods of drizzle or rain, or in high humidity. It first causes a brown discoloration, then wilting of buds, flowers, leaves, and stems.

Powdery mildew is a gray-to-white dusting on the leaves and stems that causes wilting and collapse. It grows in high humidity and cool, damp conditions.

Treat these diseases by removing and destroying damaged parts. Avoid overhead watering that can splash pathogens onto lower leaves. Plant in full sun, and ensure adequate air circulation and drainage.

Less common diseases include the following:

Dahlia mosaic virus is caused by a pathogen in the Caulimovirus genus, spread by aphids transferring infected sap from plant to plant.

It causes disfiguration and yellowing of leaves, stunted growth, and overall poor health. Remove and destroy infected plants and control aphids to prevent its spread.

Once a plant is infected, it must be removed and destroyed. Avoid sowing susceptible cultivars in the same soil.

Learn more about identifying and controlling dahlia diseases.

Darlings of the Late Garden

Bright, bold, and beautiful, dahlias are the darling of the late summer garden.

And although they require a little bit of extra care in lifting and storing tubers over winter, it’s well worth the effort for their long, showy season and vases full of gorgeous cut flowers.

How about you folks, how do you use dahlias in the garden? Let us know in the comments section below!

And for more information about growing dahlia flowers in your garden, check out these guides next:

• 19 of the Best Flowering Companion Plants for Dahlias
• Tips for Growing Dinnerplate Dahlias
• Why Dahlias May Fail to Bloom (And What to Do About It)