How to Plant, Grow, and Care for Dinnerplate Dahlias

Dahlias add drama to the summertime garden as stunning specimens and showy cut flowers. Beautiful, large blooms in an array of colors and petal arrangements make dahlias a garden standout.

Dinnerplate dahlias are the giant version of dahlias – glories in the garden with huge, showstopping blooms. Their size, color, and form give way to bold statements unparalleled in other flowering perennials. Flowers are literally the size of dinner plates and add high contrast in texture, scale, and hue.

Dinnerplate dahlias don’t get their beauty queen good looks without a little effort. With the right site preparation and tending, these dahlias serve bountiful blooms all summer long.

What are Dinnerplate Dahlias?

The descriptive term “dinnerplate” refers to any dahlia with flowers eight inches or more in diameter. These are huge blooms! Some varieties even reach 14 inches across.

In general, dahlia blooms range in size from tiny pom poms to large dinner plates. Their nearly perfect petal arrangements create symmetrical and varying forms. The American Dahlia Society classifies dahlias into decorative, ball, orchid, peony, and cactus types, all based on their petals and intricate symmetry. Ten classifications exist to organize the many features of dahlia hybrids.

Dahlias are ideal for the cutting garden or perennial bed. White they steal the show, plenty of companion plants complement dahlias. Pair them with geranium, agastache, salvia, and spring-blooming bulbs. Dahlias are toxic to dogs and cats, so keep them out of range of curious pets.

Characteristics

Dinnerplate dahlias produce different blooms (in form, size, and color) depending on the cultivar. Flowers may be single or double, full and round, cupped or flat. Dahlias bloom in every color under the sun (except blue), from creamy white to purple-black.

Dahlias bloom from midsummer to frost, with the initial bloom being the largest. Two or three bloom cycles last until early fall.

Depending on the variety, dahlias reach one to six feet tall and spread from one to three feet wide. Plants branch readily and get leggy. Pinching new growth helps foster a bushier habit.

Dahlias are perennial in USDA zones 8-10 and usually hardy down to zone 7. In colder climates, dahlias grow well as annuals. Dig tubers and store them in winter for replanting in the spring, or start with fresh plants.

Native Area

Dahlias are native to Mexico and Central America, where they grow wildly and are cultivated for the edible value of the tubers. Spanish explorers in the Mexico mountains noted dahlias in the 1500s, referencing historical applications for treating stomach ailments and other medicinal uses. 

Flowers on the original species are petite, at only one to two inches across. In the 1800s, the plant spread to Europe, and talented Dutch and Spanish hybridizers got to work cultivating them for their spectacular blooms.

Dahlias’ natural growing area has warm, sunny days and cool nights. They grow best in moderate climates with plenty of water and sunshine.

Planting

Purchase dahlia as tubers (enlarged roots) for spring planting. It’s a good rule of thumb to buy named varieties for best performance (rather than those labeled by color).

The best time to plant dahlia tubers is late winter to spring when soil and air temperatures warm. Start them early in pots indoors for planting out six to eight weeks later. 

Plant tubers right in the ground after the final frost – usually April or May and as early as March for southern climates. Later spring plantings yield beautiful fall flowers. Plant dahlias through mid-June in most parts of the United States.

If soil is naturally moist from spring rains, don’t water the tuber until new growth emerges. Too much water causes tubers to rot. If the soil is dry, keep it moist through sprouting.

It’s easy to work with dahlia tubers, which grow in containers and the garden bed. Ensure pots are large enough to support your dahlia’s mature size.

Transplanting

A key to dahlia growth is site preparation. Dig a hole 12-18 inches wide and one to two feet deep in the garden. Amend the soil with organic matter and backfill the hole. Plant dinnerplate dahlia tubers four to six inches deep – eye side up – with a generous spacing of one to three feet apart.

For tall dahlia varieties (those over four feet), the Missouri Botanical Garden recommends digging a one-foot hole, amending the soil, and backfilling it with six inches of soil. Then, plant the tuber and cover it with one inch of soil. As shoots emerge, continue covering gradually with the remaining soil fill.

To get a jumpstart on growing dahlias, start tubers in indoor containers to be moved outside after the last frost. Plant tubers in a soilless mix at crown level. Place containers in a sunny spot with cool temperatures (around 55℉ or 13°C) and keep the soil evenly moist but not wet.

How to Grow

A robust root system is essential for thriving dahlias, achievable through site selection, preparation, and pruning. Dahlias don’t like strong, drying winds, so protect those tall stems and flowers from breezy areas.

Dinnerplate dahlias require staking for their tall stalks and heavy blooms that weigh down hollow stems. Place stakes one foot in the ground at planting time, next to the roots. Use at least six-foot-long stakes, like coated steel or sturdy wood stakes. Tomato cages and netting are also helpful depending on the number of dahlia plants in your garden.

Light

Sun-loving dahlias thrive with six to eight hours of daily sunlight. In climates with intense summer sun, offer a little afternoon shade protection. 

While dahlias tolerate part shade, without sunlight they will be leggy with weaker blooming.

Water

Fast-growing dahlias are almost 75% water! They need consistent moisture and regular water throughout the growing season, usually once or twice weekly. However, they won’t tolerate wet feet. Ensure good drainage and water deeply. Increase frequency during dry spells.

Containers dry out more quickly than in-ground plantings, so check water needs regularly.  

In the ground, dahlias benefit from surface watering like drip irrigation or soaker hoses. Avoiding overhead saturation helps prevent foliar diseases. Watering deeply rather than frequently staves off slugs and other pests.

Soil

Soil is another big one for dahlias. Ideal soil is loose and crumbly, with good aeration and moisture retention. They prefer organically rich, well-drained soils. Slightly acidic soils with a pH between 6.5 and 7.0 are prime. If the soil is too acidic, add a cup of lime to neutralize.

Amend the soil with compost, leaf mold, aged manure, or pine bark at planting. Mix these with ⅔ native soil. Keep in mind that manure and pine bark can increase acidity.

In poor soils (overly sandy or clay), incorporate two to four inches of compost derived from completely broken-down plant material. Compost will help with aeration, moisture retention, drainage, and nutrition. 

Temperature and Humidity

Cool nighttime temperatures and warm days are best for dahlias to grow and flower. On average, 55-60℉ (13-16°C) nighttime temperatures and 70-80℉ (21-27°C) daytime are ideal. 

As perennials, they experience winter dormancy, reemerging in spring.

Mulching helps regulate temperatures in spring and summer by keeping roots cool and retaining moisture. Add more mulch before cold winters for overwintering protection.

Fertilizing

Dahlias grow quickly and use a lot of energy to produce those showstopping blooms. Nutrient-rich soils ensure health and vigor all season long, so dahlias with rich soils won’t need fertilizer to thrive.

That said, plants benefit from an all-purpose organic fertilizer at planting and from monthly feedings until mid-August when growth slows. A 5-10-10 or 5-20-20 organic fertilizer helps boost blooming without sending too much nitrogen into leaf production.

Pruning

Depending on the plant qualities you want to foster, dahlias benefit from light pruning as they grow. Standard techniques include topping, disbudding, and deadheading.

Topping promotes fuller plants with a leafier, less leggy habit. Pinch off the growing tip when plants reach 12 inches tall with three or four pairs of leaves. Topping promotes lateral branching and fullness.

Disbudding involves removing all the buds but one on a single stem. Do this when buds are the size of a pea. This results in fewer blooms but a large, singular flower from the central bud. Leave buds if you want more flowers and aren’t picky about the size. Clip off a few lateral branches, leaving prominent ones for the flower display. Dahlias produce more blooms than they can feed, and reducing buds directs energy to flowering.

Regular deadheading promotes flowering, with less plant energy going into seed production. And, of course, dahlias can be plucked for cut flower arrangements anytime. Clip flowers when they’re fully open for a lasting floral show.

Maintenance

These beauties are a bit high maintenance, but after soil prepping and tuber planting, a few simple garden tasks can help dahlias grow with health and vigor.

Mulch dahlias to retain moisture, promote humidity, keep roots cool in summer, and insulate roots in winter.

Use stakes for dinnerplate dahlias, installing at planting time or before plants are over one foot tall. Tie stems to stakes with soft, natural twine and continue tying them off as they grow.

Decide whether you’ll leave your dahlia tubers in the ground or dig them for winter storage. In zones 7-10, they’ll overwinter outside, though some gardeners choose to bring them inside rather than risk a cold winter.

Digging

If you’re growing a lot of dahlias, lifting the tubers for winter storage is labor-intensive but well worth it to save your investment. It’s worth it if you’re growing just a few for the following spring bloomfest.

Wait until the first few hard frosts to dig dahlia tubers in cold climates. Plants will blacken and die back, and tubers will harden off. Green tubers shrivel quickly in winter storage, so waiting through these frosts is worth it (or at least through prolonged nights of cool temperatures – mid-November or so).

When digging tubers, take care not to damage long roots or the tuber itself. They break easily at the eye when lifted. Leave a few inches of the stalk intact. Brush off dirt, rinse the tuber, and trim back roots. Allow it to dry overnight in a cool, dark place (40-50℉ or 4-10°C) before storage.

Store tubers in boxes or crates of damp newspaper, sand, vermiculite, or wood shavings. The medium should be moist but not wet, and avoid sealing tubers in plastic bags (they’ll rot). Check periodically for even moisture.

Propagation

Dahlias propagate through cuttings and tuber division. Since dinnerplate dahlia hybrids do not come true from seed, collecting and sowing seeds will yield new plants but not necessarily the same plant as the parent.

Cuttings

Dahlia cuttings are a simple way to recreate your dinnerplate beauty. In spring, wait until plants are 12 inches tall. Pull soil from the tuber and cut off “slips” (shoots other than the primary stem).

Dip the slip in rooting hormone and plant in a well-draining soil mix. Cuttings should develop roots in a few weeks. Move them to the garden, providing filtered light for the first week before full sun exposure.

Division

A single dahlia tuber will multiply by late summer in the growing season. Dividing tubers benefits the plant, as the strongest dahlias grow from a single tuber rather than a clump of tubers with multiple stems. You can easily make more dahlias while improving plant vigor!

In the fall or spring, dig tubers and divide them using a sharp blade. Tubers need “eyes” to sprout; these dots are most visible in spring. Allow cut tubers to dry overnight before storing or planting (for spring-divided tubers).

Popular Varieties

With hundreds of dahlia varieties available, honing in dinnerplates makes choosing one – or many – much more manageable. Fortunately for us, the list of dinnerplate dahlias is long. You can’t go wrong with a variety that suits your garden style and color scheme.

Dahlia ‘Kelvin Floodlight’

‘Kelvin Floodlight’ is an award-winner with spectacular clear yellow blooms that reach 10 to 12 inches across. This classic dahlia came into cultivation in 1959 and has won prizes ever since. In the 2022 growing season, the American Dahlia Society puts ‘Kelvin Floodlight’ on its list of “The Fabulous Fifty,” a compilation of varieties winning 50 or more high awards.

‘Kelvin Floodlight’ is easy to grow and recommended as a “starter” dinner plate dahlia variety. It serves up a plate of pure garden cheer from summer until frost. Plants quickly reach three to four feet tall.

Dahlia ‘Cafe au Lait’

Dahlia ‘Cafe au Lait’ is a pastel charmer with huge, tissue-like flowers ranging from milky white to peachy beige. Symmetrical petals pack 10-inch flowers in an informal, decorative form. 

Plants grow three to four feet tall. Some growers maintain that ‘Cafe au Lait’ produces small bulbs, but with dahlias, the size of the bulb doesn’t matter in producing vigorous plants.

Dahlia ‘Spartacus’

Dahlia ‘Spartacus’ makes a bold focal point in the garden and cut flower arrangement. Deep, velvety red flowers are eight to ten inches in diameter atop strong, sturdy stems. Ruffly flower petals curve slightly for a full, decorative bloom.

Gardeners prize ‘Spartacus’ for its robust growth and excellence as a cut flower (those strong stems help these big bloomers!). ‘Spartacus’ dominates the garden on towering stalks four to five feet tall.

Dahlia ‘Mingus Alex’

Dahlia ‘Mingus Alex’ brings drama to the garden through sheer bloom size and color. Eight-inch, fully double flowers are among the darkest dahlias:  burgundy red with purple undertones. Tall plants reach just over four feet.

‘Mingus Alex’ has a bushy habit and blooms readily with deadheading spent flowers. Sturdy stems hold up well in floral arrangements. 

Dahlia ‘Fleurel’

Dahlia ‘Fleurel’ is a classic beauty with ivory-white flowers reaching eight to ten inches across. Petals gently twist with a little frill, but the informal decorative blooms are grand and elegant. They emerge from yellow buds and have creamy yellow centers as if lit from within. 

‘Fleurel’ reaches three to four feet tall and compares to ‘Kelvin Floodlight’ in appearance and vigor. Plants produce a dozen or more blooms, a spectacle in the garden and long-lasting in the vase. 

Common Problems

Dahlias sometimes experience pests and diseases in the garden. Root rot and gray mold are occasional problems, as are pests like slugs, spider mites, and aphids.

Planting in full sun with plenty of air circulation and regular moisture helps stave off infections. Here’s good news – dahlias are deer-resistant! They’re not a favorite of deer or rabbits.

Pests

Aphids are common garden insects usually treated with non-chemical means. Often, they cause no plant damage, but severe infestations cause plant stress. Signs of stress include curled leaves and stunted growth. 

Slugs may also be unwelcomed dahlia visitors; they love the plants as much as we do. Set beer traps (dishes of beer that entice the slugs for a swim) at soil level or manually pick off the pests in the morning. Leafhoppers, stalk borers, and thrips are also common pests of dahlias.

If you detect insect infestation, spray the plant with a strong stream of water to deter and knock insects off the stems (taking care not to damage tall stalks and big blooms). A simple horticultural soap can rid the plant of insects, but follow label directions, as these also affect beneficial insects. 

Diseases

As with pests, the best disease control is prevention through cultural conditions. In general, problem plants should be removed from the garden to minimize chemical treatments and promote the health of surrounding plants.

Botrytis root rot is a fungal disease, especially prevalent in high-humidity conditions with limited air circulation. Brown spots and “fluffy mold” are indicators of botrytis. Take care not to overwater or overfertilize dahlias, which weakens the plant.

Powdery mildew is a common fungal disease indicated by a gray-white powdery substance on leaves, stems, and buds. Leaves may distort and drop.

Phytophthora is a fungal root rot that causes a slow decline of the plant, impacting feeder roots so they can’t uptake water and nutrients. The best control is proper cultural management, especially in not overwatering dahlia tubers.

Dahlia mosaic virus is a highly communicable disease that causes mottled leaves and distorted growth. It originates from other mosaic viruses, and vectors like leafhoppers. If you notice signs of mosaic virus, contact your extension office. They may ask for a sample of a leaf.

If your dahlias show signs of disease, remove and destroy affected plant parts and any dropped leaves. Horticultural oils like Neem can treat fungal diseases early on (but again, these impact beneficial insects, so be sure to follow application requirements). It’s best to remove the plant if infestations are severe.

Frequently Asked Questions