Most sources indicate that the cactus dahlia is a direct descendant of Dahlia Juarezii, which was introduced into European gardens by way of Holland in 1872. Over the years, some botanists have contended that it is one of the many variations springing from Dahlia variabilis, the Mexican native which first flowered in the Spanish Royal Gardens in Madrid in 1789. Whichever is the case (and it may well have both species in its family tree), the cactus dahlia appeared on the English garden scene in the late 19th Century and was all the rage there and in the United States by the first decade of the 20th Century, with many new varieties registered with the Royal Horticultural Society each year (the American Dahlia Society was founded in 1915).
Semi-cactus dahlia flowers are the most casual-appearing of the cactus dahlias. Their ray florets, which the casual observer would think were petals, are flat at the base but the edges roll toward one another for at least half their length, and are fully revolute (the edges touching or passing each other) for a quarter of their length. The depth of the bloom is ideally three-quarters of its diameter. One of the favorite semi-cactus types at Lynch Creek Farm is Pari Taha Sunrise (at left), a small flame blend that's a huge seller among the gardeners who buy dahlia tubers as well as a favorite of the late-summer bouquet-buyers.
Straight cactus flowers bear ray florets with a narrow appearance. Not only are they narrower at the base, but they extend straight outward, reflexing toward the stem so that they radiate like fireworks. The florets are uniform in length and are revolute, or rolled, for most of their length, touching or overlapping for at least half of their length.
Good examples of the straight dahlia are White Kerkrade, at right, and Bold Accent, at top of this post. White Kerkrade, named for its city of origin in the Netherlands, is a miniature with just the faintest hint of pink in the center. Bold Accent is a six-to-eight-incher with luscious variations on lavender brush-stroked on the tips of its florets.
Incurved cactus dahlias are among the most graceful of the species. Their florets, of uniform length, curve uniformly toward the face of the flower. Because of the incurved orientation of the ray florets, they are less deep than the other cactus types. Their depth is typically half of their diameter. A delightful dahlia in the garden or for cutting, Bed Head is a variation on the incurved type. Bed Head's incurved florets are unpredictably oriented, hence the name. With its four-to-six-inch blossoms, it's a great cutting dahlia, but it's beautiful in the garden as well, with lacy foliage and massive form (it grows five to six feet high).
Cactus dahlias are perfect choices for Pacific Northwest dahlia growers. The revolute florets virtually shed water, so the occasional August or September rain doesn't dampen the style of these great dahlia flowers. They have a good, hardy growing style that works well in any climate. It's not too late in most climates to start dahlia tubers; choose your dahlia color and size and get growing!