The rich variety of their flower colors, shapes and sizes added to their extensive blooming season, have turned dahlias into a popular addition to our landscapes. There are thousands of varieties of dahlias (!!!) and they are all classified by the shape, size and color of their flowers.
Flowers can be as small as 2 inches in diameter or up to one foot. They offer an impressive range of colors such as pink, purple, red, scarlet, orange, yellow, white and can be stripped or tipped with another color. They can be single-flowering (orchid-flowering, anemone and collarettes) or double flowering (cactus, semi-cactus, formal or informal decorative dahlias, ball and pompons).
Their wide height range can start as low as 12 inches and go up to 6 feet.
They thrive in full sun, prefer well-drained, sandy soils although they can grow nicely in heavy clay soils - but adding some sand or peat moss would be a good idea. Tender bulbs, they are hardy to USDA Zone 8 where they can be cut back and left in the ground to overwinter. In colder areas, they will have to be lifted after the first harsh frost and stored over the winter.
Both types have double flowers with long pointed ray petals that revolute or roll back along half their length, giving the flowers a spiky look. Most cultivars reach a height of more than 40 inches.
These are double dahlias with broad, flat-tipped petals that are sometimes wavy. The flowers are normally large and the plants easily top 40 inches tall, though there are even taller varieties. They can be formal with flat petals evenly and regularly placed throughout the flowers, or informal with generally flat petals, sometimes slightly rolled at the tips, but with irregular arrangement of formation.
Pompon and Ball Dahlias feature relatively small, fully double, globe-shaped flowers with petals blunt or slightly rounded at their tips. How not to marvel at the perfect petal arrangement of these dahlias? They display an infinite swirl of florets with fold upon fold of incredibly flawless petals.
Anemone Dahlias feature an outer ring of flat ray petals arranged in a wreath and surrounding masses of tiny, elongated disk florets which form an intriguing floral pincushion. Collarette Dahlias are small to medium flowers with large flat ray petals surrounding an open center. Within the ray and surrounding the center is a wreath of shorter petals, often of a different color: this forms the “collar.”
Single Dahlias feature blooms with a single row of flat or slightly cupped ray florets arranged in a flat plane, uniformly overlapping, preferably in the same direction with no gaps. The disc flowers may have up to three rows of bright yellow or orange pollen and the blooms are over two inches in diameter (5 cm). Pollinators love these Single-Flowered Dahlias! If you want to provide something special for bees, butterflies or other pollinating insects still active in late summer of fall, choose a Single Dahlia!
Mignon Dahlias possess the same formation as Single Dahlias except they have round ray floret tips, their disc flowers have no more than two rows of pollen and their blooms are under two inches in diameter. Perfect for small gardens or container display, Single Dahlias include the highly prized Dark-Leaved Dahlias with their masses of stunning flower colors which contrast strikingly with their deep mahogany to black foliage. Effect in the garden guaranteed!
Peony Dahlias are open centered flowers with two or more rows of petals surrounding a disc. For many years the most popular Peony-flowered dahlia was a cultivar called D. ‘Bishop Llandaff’, an heirloom variety that dates back to 1927. It has open deep-red flowers with nearly black, mahogany foliage.
Orchid Dahlias are also open centered flowers with one ray of florets surrounding a disc (Single Orchid) or a fully double bloom showing no disc (Double Orchid). The florets involute for two-thirds or more of their length.
This diverse group includes all varieties that do not fall into one of the above groups.
- Laciniated or fimbriated Dahlias present petals that are split at the end into two or more divisions.
- Stellar Dahlias present decorative shaped flowers with petals being creased causing them to be narrow and involute with a slight recurve to the stem.
- Waterlily Dahlias have fully double blooms characterized by broad and generally sparse ray florets, which are straight or slightly involute along their length giving the flower a shallow appearance.
- Dinner Plate Dahlias exhibit huge and magnificent blooms. They are unbelievably large - up to 12 in. across (30 cm) - and will bloom continuously from July until the first touch of frost. This is not an official classification, in fact, these robust dahlias are registered under several different classifications.