Dahlia Flower Information: Varieties, Overwintering, Propagation and More

An illustrated guide to growing dahlias

Reader Contribution by Michael Feldmann
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Adobe Stock/Danita Delimont

Get your dahlia flower information here! Learn to grow dahlias, from choosing beautiful varieties to planting tubers to propagating flowers.

Summer wouldn’t be summer without these lovely flowers, dahlias. Their beautiful flowers come in almost any color imaginable, from pale pastels to vibrant shades. They are also come in a range of flower shapes, from small tight balls to waterlily-like blooms the size of dinner plates. They are perfect for adding late summer color to gardens from July to October and look perfect in any style of garden. They also look especially great with summer blooming plants, such as roses, cosmos, sunflowers, rose of Sharon, hibiscus, and bulbs such as iris, lilies, gladiolus, begonias, crocosmia, and freesia. Dahlias are also very brilliant and prolific cut flowers. The more you cut them, the more flowers they produce.

I have written a guide on how to grow these lovely flowers in your garden or yard!

Dahlia Flower Information

The dahlia originated in Mexico, where it was known to the Aztecs and recorded by Europeans in the late 16th century. Two centuries, later the Spanish introduced it to Europe. It was, however, a quite different plant from the dahlia we know today.

One of the original species, Dahlia imperialis, had single lilac-colored or reddish flowers and grew in a tree-like form to a height of 6-18 feet. Smaller species were also discovered, including D. coccinea, which had single red flowers. From several of these single-flowered species, the modem plants with their large, complex blooms were developed. The plant was called dahlia in honor of the eminent Swedish botanist Dr. Andreas Dahl.

As a native of Mexico, the dahlia is a subtropical plant that requires humus-rich soil, constant watering, and regular feeding. It has tuberous roots, hollow stems, bright green to bronze-green leaves, and flowers ranging from pure white through attractive shades of yellow to the deepest maroon. Some dahlias are bicolored. There are two plant types: bedding dahlias, most commonly grown annually from seeds but also available as tubers; and exhibition, or show, dahlias, which are almost always grown from tubers.

Choosing Your Favorite Varieties

Dahlias come in many beautiful colors and shapes, from which it is amazingly easy to choose the perfect variety for your garden. Official dahlia classification identifies them by flower form, here are the several types:

Single Dahlias. Single dahlias consist of a central disc surrounded by a single row of flat or slightly curved florets, evenly spaced, without gaps in arrangement. Most flowers are over 2 inches in diameter and contain up to 3 rows of bright orange or yellow pollen, which attracts bees, butterflies, and other pollinators. They are excellent to grow in small-sized gardens and containers.

Cactus Dahlias. Cactus dahlias have astonishingly beautiful blooms, that brighten every garden. The unusual, fully double flowers of cactus dahlias have pointed tubular petals that give them a spectacular look! The blooms come in almost any color combination. Cactus dahlias are also quite hardy, having the ability to withstand inclement weather, including strong winds and heavy rains.

Semi-cactus Dahlias. Semi-cactus dahlias have flowers slightly similar to Cactus dahlias. They have fully double fluffy-looking flowers. The petals have a wider base at the bottom than cactus dahlias and are curled about half their length. Semi-cactus dahlias are great to grow in every home garden. They are also excellent as for bouquets.

Ball Dahlias. Ball dahlias are characterized by their round, ball-like blooms. The small, fully double flowers have a seemingly endless number of curved ray florets that form a perfect spiral around the center. Ball dahlias look wonderful in gardens, containers, and bouquets.

Pompon Dahlias. Pompom dahlias are remarkably similar to ball dahlias, their flowers are fully double and perfectly round. The petals are curved inward and tightly packed in rows. They produce smaller blooms than ball dahlias but are equally beautiful in bouquets.

Peony Dahlias. These fluffy, fully double flowers have a beautiful classic peony look. The center is surrounded by many rings of ray florets, which at the base are either flat or curved inward. Peony dahlias are fast-growing plants popular for garden borders. Their open flower form makes them a great plant for a variety of pollinators, including bees and butterflies.

Anemone Dahlias. This beautiful flower looks excellent in the gardens as well as in containers. The center consists of a dense group of elongated tubes. There may be one or more rows of flat flowers surrounding the center in the form of a wreath. Anemone dahlias are also great for bouquets.

Decorative Dahlias. This group consists of perhaps the most well-known of all dahlias–the Dinnerplates! The large, showy flower can be up to 12 inches long and have broad flat-topped petals, arranged in either formal (petals appear evenly) or informal (petals appear irregularly). Formal decorative dahlias are ideal for vases while informal dahlias look wonderful in borders and containers.

Collarette Dahlias. Collarettes are marked by a collar-like circle of short florets close to the center. There is an outer ring with one row of larger, flat, or curved, often overlapping florets. The open flower structure allows easy access to butterflies, bees, and other pollinating insects. Collarette Dahlias are an excellent addition to any garden!

Planting Dahlia Tubers in The Garden

Dahlias are an extremely easy plant to grow, and only several of them can provide you with plenty of beautiful flowers from summer to fall. Planting dahlias is easy, first of all, you just need to familiarize yourself with their needs such as soil, location, and others.

Soil preparation

Dahlias need full sun and rich, porous soil that retains moisture well but drains easily. Ideal soil pH is neutral to slightly acid 6.5 to 7.0. Since dahlias are heavy feeders, you will need to bury the garden bed generously with dried or well-rotted manure, compost, or other suitable organic material in the fall. Sprinkle 4 ounces of bone meal or 2 ounces of super-phosphate for each square yard. To allow frost and air to penetrate and break down the added materials, do not smooth down the soil. If the soil is not rich, apply a complete fertilizer (such as 5-10-10), according to package directions, monthly after growth begins.

Choosing the right location

Locate your dahlias in a warm, sunny spot where there is good air circulation. Dahlias grow best in a location with 6 to 8 hours of direct sunlight per day. A site with some shade from the afternoon sun will do. And also, locate your dahlias in a location with a bit of protection from the wind.

Spacing

Dahlias should not be planted too close together, there should still be space between the plants, this ensures adequate ventilation of the leaves, which prevents plant diseases. It also makes it easier to pick the flowers for bouquets and other work on your dahlia plants. Allow 2 to 3 feet between tubers for tall dahlias (4 to 5 feet), 2 feet between medium plants (3 to 4 feet), and 15 inches between for shorter ones.

How and when to plant dahlias tubers

Plant your dahlia tubers as soon as the danger of frost no longer exists–mid to late spring is best in most areas. New growth comes from eyes at the base of the previous year’s stem. Each stem has several tuberous roots. These can be planted as a clump or divided into single tubers. In the planting bed insert a 1-inch-square stake long enough to support tall plants. In front of it dig a 6-inch-deep hole. Prepare a mixture of half peat moss and half soil and incorporate about a handful of bone meal. Fill the hole with this mixture to a level that will bring the tuber’s eye to about 2 inches below the surface. Place the tuber in front of the stake with the eye against it. Cover the tuber to ground level with the soil and peat moss mixture. Firm the soil gently over the tuber. Do not water until new growth begins. You can also label the stake with the variety name.

The tubers can also be started into growth indoors ahead of time. If more plants are needed, divide tubers when the new shoots are about 3/4 inches tall. Harden the plants before planting them out.

Caring for Beautiful Dahlias

How to fertilize dahlias

Soil that has been well fed before planting will not need much additional fertilizer during the growing season. Mulching with rotted manure or rich compost will help to develop the growth of the plants if the soil is poor or if extraordinary blooms are the objective. An additional feeding can be given when bedding dahlias show their first buds or, in the case of exhibition dahlias, after they have been pinched out for the second time. For quick results, use a 20-20-20 fast-release liquid fertilizer. For a slower response, scatter a handful of 5-10-10 around the plant.

Too much nitrogen at this time of year will encourage an overabundance of foliage rather than flowers and can reduce the winter storage quality of the tubers as well. After feeding the dahlias with any dry fertilizer, water them well to make sure that the nutrients are carried down to the root area.

It can be helpful to feed the plants every two to three weeks until the end of summer. If you plan to store the tubers, feed the soil in late summer or early fall with a mixture of equal parts of superphosphate and sulfate of potash.

How much to water dahlias

Mulch your plants to keep weeds away. When the plant is about 1 foot high, put a 1-inch layer of mulch around the base but not against the stem. This helps to keep down weeds and retain moisture. Use materials such as wood chips, buckwheat hulls, cocoa shells, or clean, dry straw. Apply in thin layers and let each dry before applying a new one. Do not mulch too early. Wait until the plants have grown to a height of 1 foot. When the mulch is applied, the soil should be moist, and immediately after it should be well soaked. If weeds appeared before mulching, remove them by hoeing, which will also keep the soil aerated. Do not cultivate more than 1 inch deep.

Water your dahlias thoroughly as the buds develop. When your dahlia tubers are first planted, watering represents a danger to them–it can cause the tubers to rot. The search for moisture does not harm the roots. For best results, give your dahlias more moisture as their flowering season approaches. In dry spells, the plants should be watered freely, whether or not they are coming into bloom.

When the weather is hot and sunny, water every five days or so on heavy clay soils. Lighter soils dry out more quickly and the plants should be watered about every three days. Use an automatic sprinkler that throws a fine spray up high enough for the water to fall vertically on the plants or a soaker hose laid through the plants. Any of these will provide the necessary thorough soaking of the area around the dahlias.

If you use a can or hose, give about 3 gallons of water to each plant when they are 2 to 3 feet apart; use a little bit less if they are set closer together.

Growth and maintenance

Add supports as the dahlias grow. Dahlias need support to prevent wind damage. Two or three weeks after planting, loop string around each stake 4-8 inches above the ground. Tie each plant around the stem in a figure-eight pattern. Fasten the knot against the stake. As the plants grow, make further ties up the stem. Make sure the bottom ties are not too tight around the main stem. To prevent damage to the side growths, insert thin canes firmly in the ground–three in a triangular pattern around the main stake and about 9 inches from it–sloping out. Wrap a soft string around these canes to support the side growths.

Pinching out and disbudding the big Dahlias: Most exhibition or large-flowered dahlias send up strong, center shoots but develop little side growth until the center shoots have flower buds. To encourage side growth and more flowers, pinch out the center shoots two or three weeks after planting. The center shoot is the growing tip of the stem. Usually, this is done in late spring or early summer for tuber-grown plants.

In two weeks or so half a dozen side shoots should have developed in the leaf axils. Remove the top pair of shoots to promote growth in the lower side shoots. These will each produce a terminal bud and several side buds. To encourage big flowers, remove the side buds as soon as they are large enough to be removed without harming the tip buds. To promote longer-stemmed side shoots and to encourage more growth in the upper part of the dahlias, cut off all the leaves that develop on the main stem a few inches from the ground.

What can go wrong with Dahlias? Dahlias are affected by several viruses, notably the dahlia mosaic virus, which causes yellowing foliage and sometimes stunted plants. It is transmitted by aphids. Spotted wilt virus causes spots and rings on leaves; it is carried by thrips and affects a range of plants. Watch for thrips and aphids early in the season and spray if necessary. Snails love dahlia foliage and flowers so take care to control them. They will climb up into the plant and stay there: if plants are being damaged, search for snails on and under the leaves and take them away, or use slug bait, making sure it is positioned out of the reach of pets and wildlife. Earwigs can also damage blooms, feeding mainly at night and causing ragged holes in petals or distorted blooms. During the day they can be trapped in upturned pots stuffed with a straw positioned on stakes amongst the plants.

Overwintering Dahlias

Dahlias are tender annuals, but they are very easy to overwinter. In fall, after the first frost has occurred, cut off all but 2 to 4 inches of top growth, and carefully dig up the tubers. Allow the tubers to dry for several days in a frost-free place away from direct sunlight. Once it is dry, remove any excess soil, leaving 1-2 inches of stem.

Store the tubers in a ventilated box or basket, filled with slightly moistened sand, peat moss, or vermiculite, and place it in a cool, dry location with temperatures that remain between 45- and 55-degrees Fahrenheit. Check tubers periodically through the winter for rotting and drying out. It is advisable to inspect the tubers every few weeks during the winter to check for disease or Shriveling. If your tubers appear shriveled, spray them lightly with water. If some start to rot, trim the rotted portion of the tubers so it will not spread.

In the early spring, when the warm weather arrives, you can successfully plant your overwintered tubers and enjoy their beautiful blooms again and again.

Propagation

There are three ways of propagating dahlias including propagating by cuttings, propagating by dividing tubers, and propagating by seeds. The method you choose depends on how many plants you want to grow and how much time you are willing to invest.

Propagating dahlias by cuttings

Taking cutting is a tried and tested way of propagating many plants and also works excellent with dahlias. Propagating dahlias by cuttings is slightly different from general propagation by cutting.

To begin, bring your overwintered dahlia tubers in about late January or early February. It is recommended to choose the firmest and healthiest tubers. Plant the tubers in a plastic planting tray filled with a damp potting mix or a mixture of half peat moss and half sand. For the best result, plant your tubers in a tray with a depth of about 6 inches or 15 cm. Make sure that the tray has several drainage holes. If you plant only a few tubers, you can use pots instead, one-pot per tuber. Plant your tubers in rows about 4 to 6 inches apart, with each stem 1 to 2 inches above the surface of the soil. Then place the tray or pot with tubers in a warm, sunny room, but avoid direct sunlight.

Watch for eyes to appear, which generally takes about 7 to 10 days (about 1-1/2 weeks). However, some may sprout sooner, while others may take a month or more. When the shoots have three or more sets of leaves, then here is the time to take cuttings. Use a sharp, sterile, knife to cut off the shoot with a narrow sliver of the tuber. Remove the lower leaves, leaving the top two leaves intact. Dip the bottom of the cuttings in natural rooting hormone. Then plant your cuttings in a pot filled with a mixture of half potting mix and half sand. Water them carefully to keep the planting medium moist, but not soggy. Next, place the pots with cuttings in a warm room. The cuttings will start root in about 2 to 3 weeks. At this point, you can allow them to develop a bit more, or you can plant them directly into the garden if the weather permits.

Dividing dahlia tubers

Propagating by taking cuttings produces more new plants, but propagating by dividing tubers is easier, so if the need is for only a few new plants, dividing tubers is best. For each new plant, you will need one section of the tuberous root and a piece of the stem with an eye in it. New growth comes from this eye. Each plant needs only enough tuber to keep the plant growing until new roots form. A single piece of tuber with a single piece of stem attached is best. Too large a section of the tuberous root will delay the formation of new roots, and the plant will produce a mass of leafy growth, which will further result in few and inferior blooms. Before cutting the clump of tubers, examine each stem to locate the eyes. If they prove difficult to locate, place the tubers in damp peat moss or soil, and keep them in a warm place for a few days to give the buds time to develop. As soon as the eyes or buds are visible, use a sharp knife to cut down through the stem, doing your best not to damage any of the eyes in the process. Dust raw cuts thoroughly with sulfur to prevent rot. The best time for planting in most areas is late spring to early summer–or as soon as all danger of frost is past.

Starting dahlias indoors from seed

Propagating dahlias from seeds is an easy and fun way, but it takes a little bit longer than others. Seeds are sold for both small bedding dahlias and tall exhibition types, but they will not run true in color or form. To start a collection of exhibition dahlias from seeds, plant them one year, and save the tubers of the best plants for the next year. Start seeds in early spring if an indoor space or a warm greenhouse is available. In a cold frame plant four to six weeks before the safe outdoor planting date. Prepare pots or flats of sterilized soil or seed-starting mixture, level the surface, and firm it. Water thoroughly. Thinly sprinkle the seeds over the surface and cover them with about 1/4 inch of vermiculite. Cover the pots or flats with glass shaded by brown paper or with a plastic bag.

Set in a warm place in a greenhouse or in a dark, warm room to germinate — in 10 to 21 days (about 3 weeks). When the seedlings are up, remove the glass or plastic. If you are growing them indoors, set them on a sunny sill. When the seedlings are sturdy, transplant them to individual 3-inch peat pots filled with potting soil. Once established, they can take full light and sun. If the plants are being grown in a cold frame, harden them their several weeks before setting them out. If there is no cold frame, set them in a dependably warm, sunny spot outdoors for a week before planting.

Keeping these various points in mind, you will easily be able to choose the right location, plant your dahlia tubers, fertilize and water them properly, get rid of pests and diseases, propagate them correctly, and finally enjoy lots of blooms throughout the year.


Michael Feldmann is a farmer and writer in Oklahoma, who studies agriculture and has worked as a journalist for magazines and newspapers around the country. His writing has been published in Acres USA, Rural Heritage, Farming magazine, Farmers Weekly, Permaculture magazine, MOTHER EARTH NEWS, and as a column in Poultry World.


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