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By the late 1700’s, many travelers to the new world had noted big beautiful flowers in the late summer and fall unlike anything available in Europe. Botanical gardens in Spain and the Netherlands requested seeds and tubers be sent from Mexico. Many seeds remained viable, but only one of the tubers survived the trip. All modern Dahlia hybrids are the progeny of those few seedlings and one tuber.
Many gardeners find that August gardens often look tired or lack color. A dahlia grower will surely never have this problem. Dahlias are so big and vibrant that August is transformed into summer’s biggest show. The tubers also lend themselves so readily to division that a gardener starting with just a couple dahlias who digs and divides them each fall will soon find that their garden is full and bright from August to frost and they have tubers to share with friends and neighbors.
Thanks to a great deal of breeding work, there is a dahlia for every sunny part of the garden and every color scheme. The blooms have been divided into 19 different types which are available in every color except blue. They range in height from dahliettas which barely reach 12” and are well suited to containers, to dahlia imperialis which reaches 12’ in a single season.
Since they don’t sprout until early June, dahlias are the perfect border companion for spring bloomers which go summer dormant like Aquilegia (Columbine), Papaver (oriental poppy), or tulips. Dark leaved varieties add contrast to the garden even before their bloom time begins.
The best selection of dahlias is available with the spring bulbs from February through April. These come as tubers and should be stored in a cool, dry place until mid May when it is safe to plant. Some of our favorites that were available this year as tubers are:
Thymus pseudolanuginosus (Wooly Thyme) – Evergreen 1-3 feet tall, and 3 feet wide, forms low-spreading mat of wooly leaves, sparse scented pink flowers bloom in early summer. This variety is often planted between rocks.
‘Sunshine’ which is mignon single* flowered and has coppery orange petal tips with a red center. Flowers are 3-4” in diameter, and the foliage is bronzy purple.
‘Fleurel’ which has an informal decorative* white flower capable of reaching 10” in diameter.
‘Soulman’ which is anemone-flowered* and has deep burgundy almost black blooms 4-6” in diameter.
‘Bishop of Llandaff’ which has black foliage and red peony* flowers 3-4” in diameter.
‘Black Wizard’ which has a red-petaled black-centered cactus* flower which can reach 12” in diameter.
‘Café au Lait’ which is a unique creamy peach shade of informal decorative* flower. Blooms can reach 10” in diameter.
‘Hawaii’ which is an unusual mottled informal decorative* flower of white, raspberry, and yellow which can reach 10” in diameter.
We also get some Dahlias as growing plants throughout the summer, if they are grown from tubers or cuttings, we stock them with the perennials, and they should overwinter successfully with good drainage. Some are also grown from seed, these grow only small tubers that don’t overwinter well in the ground (though you can still overwinter them by digging and storing), and so we keep them with the annuals. Some of our favorites as started plants are:
The Mystic Series: Dark foliage with red, yellow, pink and white, or orange informal decorative* blooms on compact plants to about 2’ tall.
Dahlia Imperialis or D. Tenuicalis Tree dahlias grow huge bamboo-like stems up to 4” across and can reach 18’ in a season. D. Imperialis grows taller and blooms later. D. Tenuicalis grows slightly shorter and blooms earlier.
Dahliettas are low growers well suited to container culture, they are only available as growing plants, and come in a range of colors and bloom types. Due to their small stature they start blooming earlier than their larger relatives, but still carry on blooming until frost.
‘Xera Dark Leaf mix’ are dwarf (about 20” tall) dark leaved, mignon single* flowered types that come in a variety of colors and leaf shapes.
‘Bishop’s Children’ are seedlings of the variety ‘Bishop of Llandaff’ which retain the dark foliage of that parent, but come in a number of peony-flowered* colors.
‘Figaro Mix’ is a low growing (12-14” tall) mix of single and double flowered dahlias in a variety of warm colors.
'Halequin mix’ is a dwarf (12-14” tall) mix of bicolor collarette* flowered dahlias. Yellows, oranges, pinks, purples, and white prevail, with each flower usually showing two of these colors.
*denotes a particular form of dahlia bloom as recognized by the American Dahlia Society, please see the Dahlia Society website for a sample of each form.
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Origin: Dahlias are native to Mexico, Central, and South America.
Culture: Full sun with moisture retentive but well drained soil. Use compost and bone meal at planting (and pumice if the tubers will stay in the ground over winter), and water about 1” once a week in early summer and fall, and twice a week through the hottest part of summer.
Despite being natives of Mexico, Dahlias do not appreciate hot, dry weather. In the wild, they are found in foothills where the temperature is always moderate, and summer rains are frequent. These are the conditions we must strive for when growing dahlias.
When we plant tubers or started plants in spring, the soil is cooler and moister than ideal (if planting tubers, do not water on planting, wait for them to sprout) and so good drainage should be encouraged by mixing pumice and compost into the planting area.
At planting is also the best time to drive a sturdy stake appropriate to the expected height of the dahlia in the ground nearby.
Dahlias respond best to low nitrogen fertilizers such as bone meal or bulb food at planting and perhaps once more during the summer. Giving low nitrogen fertilizers will encourage blooming without promoting excess growth.
Basic Maintenance: Little maintenance is required for dahlias to be the stars of the late summer and fall border, however, a little extra attention will definitely pay off. If one is to keep maintenance to a minimum, then some care should be taken at planting time (see planting instructions in the culture section).
If planted as indicated above, annual maintenance need consist only of watering deeply once a week (maybe twice if it’s particularly hot) and cutting plants to the ground when frost kills the top in the fall.
Deadheading (removing spent flowers as they appear), or better yet, taking cut flowers of blooms which are fully open will help direct energy to forming new flowers and will give you a beautiful bouquet which will last 4-6 days in water. To make the cut flowers last scald the cut stems in very hot water (180 degrees).
Digging, storing, and dividing is optional, but can prolong the life of plants, enhance their flowering, and ensure their survival through the winter. When frost kills the top of the plant, or on November 15th if we still haven’t had a frost, cut the plant about 6” above the soil surface and carefully dig up the tubers.
Remove as much soil as you can from the tuber, then put it in a place where there is good airflow but it is protected from potential rain (such as a covered porch). Leave it there for 2 days, until the outer surface is dry to the touch. For storage, put tubers into cardboard boxes with shaved wood animal bedding or peat moss on all sides.
Store your tubers in the coldest possible place that you know will not freeze, if they freeze they will die. Around May 15th, remove the tubers from storage, and look for the eyes, which range from little pink or green bumps to obvious sprouts which are starting to form. The dahlia can be divided into as many pieces as there are eyes. The most vigorous plants will come from the eyes with the most tuber still attached.
Propagation by Cuttings: Dahlias can also be propagated by cuttings, the most effective ones are taken when the sprouts are 2-3” tall.
Propagation by Seed: Dahlias produce viable seed if you don’t deadhead them. If more than one dahlia is present, seedlings will be different from both parents. To save seed, do not deadhead, wait for the spent flower head to change colors from green to straw yellow, then peel back the outer sepals and look for seeds near the base.
Pests and Diseases: Slugs and snails love dahlias, apply Sluggo or set out beer traps starting around mid May for tubers left in the ground, or at planting time for new plants. Once the plants are up and growing damage is usually minimal.