How to Grow Dahlias

Dahlias are native to Mexico, Central America and northern South America and they're members of the aster family (Asteraceae). Dahlias grow from a type of bulb called a tuber that is a fleshy underground root. Outside of hardiness zone 8, treat dahlias as annuals by digging up the tubers, storing them through winter and replanting them in spring.

Dahlias dazzle in many facets of the garden. They're stunning massed in borders and make lovely accents throughout. They grow well in containers, too.

Dahlia blooms attract butterflies, bees and hummingbirds, making them an excellent addition to a pollinator-friendly garden.

Dahlias thrive in climates without weather extremes, preferring temperatures up to 80 degrees Fahrenheit during the day and around 60 degrees Fahrenheit at night. Warm evening temperatures above 85 degrees stress the plants, leading to susceptibility to pests and diseases.

While dahlias prefer temperate areas, they will grow in a variety of climates and conditions. If you garden in a warmer zone, try to find a microclimate in your garden that protects the plants from late afternoon sun. Dahlias like full morning sun and dappled afternoon light. Planting dahlias under trees (in containers or in ground) works well, using the tree's shade to protect dahlias from harsh summer sun.

Grow dahlias in containers or in garden beds. The keys are to have rich, well-draining soil and the right light. Dahlias grow best in full sun, but need protection from hot, late afternoon sun. If you live in a hot climate, position dahlias to get shade from trees, buildings or structures like pergolas in the hottest part of the day.

Once you have a site in mind, you can choose to grow dahlias from tubers or buy container-grown plants. Dahlia tubers are available for sale in late winter and spring. Gardeners plant them throughout spring and summer for late season blooms. For instant color impact, look for container-grown dahlias available in Garden Centers in early summer, with selections varying by region.

Plant tubers outside as early as two weeks before your average date of last frost in spring, as long as the soil is dry and workable. If you'd like, you can start them earlier indoors in pots with plenty of organic, well-draining potting mix.

Take time to make smart decisions before you plant dahlias. You want rich, well-draining soil. It's always a good idea to run a soil test with a new garden and follow up with the recommended amendments. Soil tests are available from the Garden Center or from your local Cooperative Extension Service. Even without a soil test, working organic compost into the soil will help your dahlias grow.

When you're ready to plant, look at product information for the mature size. Dahlias range in height and that affects planting depth. Taller varieties are planted 6 to 7 inches deep, and shorter varieties 2 to 3 inches deep. Plant dahlia tubers about 1 to 3 feet apart, according to recommendations for your varieties.

Use a sharp knife to cut dahlia tuber clumps into sections. The growing bud is called an "eye" and it's found where the tuber joins with the stalk of last season's growth. When you plant dahlias, make sure the eyes are pointed upwards.

Steps for planting dahlias:

• In a sunny, well-draining area, dig a hole several inches deep. Amend with organic compost.
• Plant dahlia tubers with eyes facing upwards and cover with soil.
• Place a plant marker with the dahlia's type alongside the planting hole.
• Place a stake next to the dahlia. While smaller varieties may not need staking, the taller ones will. It's best to put stakes in the ground at planting time.
• You can add a slow-release granular fertilizer at planting time.

Dahlias grow large blooms on slender stems and that makes the top-heavy blooms prone to damage from rain and wind. Protect your blooms by staking them first. There are many ways of staking dahlias, but perhaps the easiest way is to use a grow-through plant support. This is a metal grid on a hoop that’s supported by metal posts that are a few inches from the ground. Individual plant supports, often used for floppy peonies, are effective dahlia stakes, as well.

When growing dahlias in a cut flower garden, try using grow-through plant trellis netting to keep the plants upright through all kinds of weather.

Tip: If slugs and snails are a problem in your garden, set out organic slug and snail bait when you plant. Dahlia tubers are susceptible to damage from these pests.

While dahlias are native to tropic regions, they will wilt in hot temperatures. Dahlias are at their best from late summer to fall, when afternoon sun is very intense. To extend the bloom time, keep dahlias' roots cool with a blanket of mulch and provide ample water. Drip irrigation will help keep mass plantings of dahlias at their peak.

In addition to overhead shade from trees and structures, you can mulch the soil to cool the plants’ roots. Dahlias have shallow roots and a blanket of mulch goes a long way to keep the moisture in the soil and cool the roots.

Water dahlias at planting but hold off on additional watering until they’ve sprouted. Once the plants are growing, water consistently and deeply. The amount depends on your climate and rainfall. To determine when your plants need water, get in the habit of observing your plants and pressing a finger into the soil about an inch. If the soil feels dry, then it’s time to water.

Always water dahlias at the base of the plant. Early morning watering is best because it reduces the opportunity for plant diseases to take hold.

The best fertilizer for dahlias is soil that’s rich in organic matter. You can supplement the soil with a slow-release fertilizer at planting time. Throughout the growing season, depending on the amount of dahlias you’re growing, use a low-nitrogen fertilizer to encourage blooms. (Nitrogen is the N in the N-P-K ration on the fertilizer bag. Look for a low N number in relation to the P and K).

Both pruning and deadheading dahlias are essential tasks that promote healthy growth and abundant blooms. Regularly removing spent flowers, known as deadheading, redirects the plant's energy from seed production back to creating more blossoms. To deadhead, simply use clean gardening shears to cut the faded flower back to the nearest leaf node or side bud. Deadheading keeps the plant tidy and encourages continuous blooming throughout the growing season.

Disbudding dahlias is a targeted pruning technique used to enhance flower quality, particularly for display or competition blooms. To disbud dahlias, closely inspect the plant stem and identify the primary central bud and the smaller side buds flanking it. Gently pinch off the side buds using your fingers or small scissors, leaving only the central bud to grow. The plant's resources will channel into the single flower, resulting in larger blooms.

For the best results, start disbudding early in the growing season when buds are small and easier to remove. For larger dahlia varieties, like dinner-plate dahlias, disbudding is beneficial to produce their signature oversized flowers. Be consistent and regularly monitor the plant for new side buds that may emerge. It's a simple task that will result in bigger, more beautiful blooms.

Dahlias can be an expensive crop to grow and require special care to survive winter. For this reason, gardeners outside of zone 9 will dig up the tubers and overwinter them in a protected space.

For best results, be careful when digging up the tubers. The "eyes" (growth buds) are in the space connecting with the underground stem. When the tubers are pulled or broken off, the eyes can be lost and the tubers are no longer viable.

When you dig up the dahlia tubers, you'll need to divide them. Do this by taking a sharp knife and cutting them so that each new tuber has an eye.

Proper digging and dividing ensures your dahlias' health and blooms for the following growing season. Here's a guide based on regional climates:

Northern Regions

In colder climates like the northern U.S., dig up dahlias before the first hard frost. Start by cutting back the plants to about 4 to 6 inches above the ground. Carefully dig around the base to avoid damaging the tubers and lift them from the soil. Gently brush off excess dirt and allow the tubers to dry fully in a cool, shaded area. Store the tubers in a well-ventilated, frost-free space, such as a basement or garage, packed in vermiculite to prevent drying out.

Southern Regions

For southern regions with mild winters (up to hardiness zone 8), dahlias can often remain in the ground. However, it's essential to provide a layer of mulch, up to 6 inches of straw, leaves, or bark that will insulate the soil and protect the tubers from occasional frost. Ensure the area around the plants drains well to prevent rot from excess moisture.

Coastal Climates

On the West Coast and similar temperate areas, dahlias may require minimal winter preparation. Pruning back the plants and adding a light layer of mulch can help protect the tubers. For areas with rainy winters, consider lifting the tubers to avoid waterlogging and rot.

Proper winter care of dahlias not only helps the plants survive but also ensures vibrant blooms come spring and summer. Adjust your care based on your region’s specific climate, and you’ll be rewarded with healthy, thriving dahlias each year.

Dahlias make exquisite cut flowers. However, they don't have a long vase life, usually just 3 to 5 days, depending on the variety. To get the most out of your dahlia blooms, follow these tips.

Cut dahlia blooms in the cool of the morning, when the plant's not stressed by heat. Take sharp, clean pruners or garden shears and a bucket of very warm water (between 160 and 180 degrees Fahrenheit) with you into the garden.

Dahlia flowers will not open once they're cut, so choose blooms that are open or nearly open. Look for stems that are long enough for your display.

Use the shears to cut the stem just above a set of leaf nodes and side buds. Place stems in warm water. When you've gathered your dahlias, bring them to your work station (can be a kitchen sink).

Replace warm water in bucket with fresh room-temperature water. To condition dahlia stems, dip them into boiling water for 7 to 10 seconds, taking care to keep the blooms away from the steam. Place the conditioned dahlias in a bucket of cool water. If you have access to a walk-in cooler, you can keep them for several days at 40 degrees Fahrenheit.