Dahlia is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico. There are 42 species of dahlia, with hybrids commonly grown as garden plants. Flower forms are variable, with one head per stem; these can be as small as 5 cm (2 in) diameter or up to 30 cm (1 ft) (“dinner plate”). This great variety results from dahlias being octoploids—that is, they have eight sets of homologous chromosomes, whereas most plants have only two. In addition, dahlias also contain many transposons—genetic pieces that move from place to place upon an allele—which contributes to their manifesting such great diversity.
The stems are leafy, ranging in height from as low as 30 cm (12 in) to more than 1.8–2.4 m (6–8 ft). The majority of species do not produce scented flowers or cultivars. Like most plants that do not attract pollinating insects through scent, they are brightly colored, displaying most hues, with the exception of blue.
The dahlia was declared the national flower of Mexico in 1963. The tubers were grown as a food crop by the Aztecs, but this use largely died out after the Spanish Conquest. Attempts to introduce the tubers as a food crop in Europe were unsuccessful.
Dahlias are annual blooming plants, with mostly tuberous roots. While some have herbaceous stems, others have stems which lignify in the absence of secondary tissue and resprout following winter dormancy, allowing further seasons of growth. As a member of the Asteraceae the flower head is actually a composite (hence the older name Compositae) with both central disc florets and surrounding ray florets. Each floret is a flower in its own right, but is often incorrectly described as a petal, particularly by horticulturists. The modern name Asteraceae refers to the appearance of a star with surrounding rays.
In the language of flowers, Dahlias represent dignity and instability, as well as meaning my gratitude exceeds your care.
May 29, 2018
2018 Belgium, Brand Florex bought on sale (1 euro a packet) from brico
Diseases and Problems
Slugs and snails are serious pests in some parts of the world, particularly in spring when new growth is emerging through the soil. Earwigs can also disfigure the blooms. The other main pests likely to be encountered are aphids (usually on young stems and immature flower buds), red spider mite (causing foliage mottling and discolouration, worse in hot and dry conditions) and capsid bugs(resulting in contortion and holes at growing tips). Diseases affecting dahlias include powdery mildew, grey mould (Botrytis cinerea), verticillium wilt, dahlia smut (Entyloma calendulae f. dahliae), phytophthora and some plant viruses. Dahlias are a source of food for the larvae of some Lepidoptera species including angle shades, common swift, ghost moth and large yellow underwing
- Slugs and snails: Bait 2 weeks after planting and continue to bait throughout the season.
- Mites: To avoid spider mites, spray beginning in late July and continue to spray through September. Speak to your garden center about recommended sprays for your area.
- Earwigs and Cucumber Beetle: They can eat the petals though they do not hurt the plant itself.
- Deer: Find a list of deer-resistant plants to grow around your dahlias.
- Powdery Mildew: This commonly shows up in the fall. You can preventatively spray before this issue arises from late July to August.
- Select a planting site with full sun. Dahlias grow more blooms with 6 to 8 hours of direct sunlight. They love the morning sunlight best. Choose a location with a bit of protection from the wind.
- Dahlias thrive in rich, well-drained soil. The pH level of your soil should be 6.5-7.0, slightly acidic.If you have a heavier soil, add in sand, peat moss or bagged steer manure to lighten and loosen the soil texture for better drainage.
- Bedding dahlias can be planted 9 to 12 inches apart. The smaller flowering types, which are usually about three feet tall, should be spaced two feet apart. The taller, larger-flowered dahlias should be spaced three feet apart.
- The planting hole should be slightly larger than the root ball of the plant and incorporate some compost or sphagnum peat moss into the soil. It also helps to mix a handful of bonemeal into the planting hole. Otherwise, do not fertilize at planting.
- Dig a hole that’s about 6 to 8 inches deep. Set the tubers into it, with the growing points, or “eyes,” facing up, and cover with 2 to 3 inches of soil (some say 1 inch is adequate). As the stem sprouts, fill in with soil until it is at ground level.
- Tall, large-flowered cultivars will require support. Place stakes (five to six feet tall) around plants at planting time and tie stems to them as the plants grow.
- Dahlias start blooming about 8 weeks after planting, starting in mid-July.
- Do not water the tubers right after planting; this encourages rot. Wait until the sprouts have appeared above the soil to water.
- There’s no need to water the soil until the dahlia plants appear; in fact, overwatering can cause tubers to rot. After dahlias are established, provide a deep watering 2 to 3 times a week for at least 30 minutes with a sprinkler (and more in dry, hot climates).
- Dahlias benefit from a low-nitrogen liquid fertilizer (similar to what you would use for vegetables) such as a 5-10-10 or 10-20-20. Fertilize after sprouting and then every 3 to 4 weeks from mid-summer until early Autumn. Do NOT overfertilize, especially with nitrogen, or you risk small/no blooms, weak tubers, or rot.
- Bedding dahlias need no staking or disbudding; simply pinch out the growing point to encourage bushiness, and deadhead as the flowers fade. Pinch the center shoot just above the third set of leaves.
- For the taller dahlias, insert stakes at planting time. Moderately pinch, disbranch, and disbud, and deadhead to produce a showy display for 3 months or more.
- Dahlia foliage blackens with the first frost.
- Dahlias are hardy to zone 8 and can be cut back and left in the ground to overwinter; cover with a deep, dry mulch. Elsewhere, the tuberous roots should be lifted and stored during the winter. (Some readers find, however, that dahlias will survive in zone 7 if the winter isn’t too severe.)
The commonest pollinators are bees and small beetles
Dahlias grow naturally in climates which do not experience frost (the tubers are hardy to USDA Zone 8), consequently they are not adapted to withstand sub-zero temperatures. However, their tuberous nature enables them to survive periods of dormancy, and this characteristic means that gardeners in temperate climates with frosts can grow dahlias successfully, provided the tubers are lifted from the ground and stored in cool yet frost-free conditions during the winter. Planting the tubers quite deep (10 – 15 cm) also provides some protection. When in active growth, modern dahlia hybrids perform most successfully in well-watered yet free-draining soils, in situations receiving plenty of sunlight. Taller cultivars usually require some form of staking as they grow, and all garden dahlias need deadheading regularly, once flowering commences.
- Giant flowered cultivars have blooms with a diameter of over 250mm.
TAKING UP THE TUBERS
In cold regions, if you wish to save your plants, you have to dig up the tubers in early fall and store them over the winter.
Dahlias may be hardy to USDA Zone 8. There, they can be left in the ground to overwinter. In areas that get frost, including most parts of Zone 5, a killing frost—or a touch of frost—can help the bulb to shut down/go dormant.
- Foliage should be cut back to 2 to 4 inches above ground and lifting and separating should be completed.
- Gently shake the soil off the tubers.
- Cut rotten tubers off the clump and leave upside down to dry naturally.
- Pack in a loose, fluffy material (vermiculite, dry sand, Styrofoam peanuts).
- Store in a well-ventilated, frost-free place—40 to 45 degrees F is ideal, 35 to 50 degrees F is acceptable.
- Take out the tubers in the spring, separate them from the parent clump, and begin again.
- If this all seems like too much bother or you do not have the right storage place, skip digging and storing, and just start over by buying new tubers in the spring.
In Mexico used as a source of food by the indigenous peoples, and were both gathered in the wild and cultivated. The Aztecs used them to treat epilepsy, and employed the long hollow stem of the (Dahlia imperalis) for water pipes
Today the dahlia is still considered one of the native ingredients in Oaxacan cuisine; several cultivars are still grown especially for their large, sweet potato-like tubers. Dacopa, an intense mocha-tasting extract from the roasted tubers, is used to flavor beverages throughout Central America
In Europe and America, prior to the discovery of insulin in 1923, diabetics—as well as consumptives—were often given a substance called Atlantic starch or diabetic sugar, derived from inulin, a naturally occurring form of fruit sugar, extracted from dahlia tubers. Inulin is still used in clinical tests for kidney functionality.