We need dahlias that will integrate with neighboring perennials, shrubs, and summer bulbs; dahlias with flowers that look more natural and plants that have more resilience. We need heirloom dahlias and modern dahlias in a similar style.
Dahlias have been valued for millennia. In Mexico and Central America, the indigenous peoples ate the tubers of the wild species and used the fat hollow stems as water pipes. Though dahlias were introduced from the Old World to the New in 1525, the colorful versions grown in gardens today date back no further than the 1800s when selections were made to combine a long season of summer color with intriguing flower shapes. Their enduring popularity attests to their toughness.
Dahlia hardiness depends on the site in which they are grown. Theoretically hardy to USDA Plant Hardiness Zone 7, the tubers tend to rot in wet winter soil. More damaging are slugs, which crawl down the holes where the stems have died and then eat the tubers. So, even in Zone 8, lift the tubers after first frosts have blackened the foliage, remove the stems, brush off the soil, and store the tubers in a frost-free place until spring.
Plant dahlias in full sun, or with a little shade in hot and humid areas. They prefer a rich, fertile soil and regular watering and feeding (I use tomato feed). A mulch of 2 to 4 inches of bark chips helps keep the shallow-feeding roots cool.
Most varieties will need support, as they can produce a great deal of heavy growth by season’s end. A stout stake knocked in alongside the tuber at planting time will be hidden as foliage develops yet provide an anchor to which individual stems can be tied with twine.
There are no rules about what qualifies as an heirloom dahlia. If a variety has been around for a long time, it would seem to qualify. Heirloom cultivars range from single-flowered types including ‘Union Jack’ in red and white stripes (1882) and partially double varieties including the scarlet ‘Bishop of Llandaff’ (1927) to fully double varieties in many styles.
There are also some fine modern dahlias in the old heirloom style. At 2 to 3 feet tall, selections in the Fordhook Garden Mix feature single and semidouble flowers in rose purple, salmon orange, scarlet, and yellow above bronze or dark green foliage. And perfect for a small yard or in containers, the Mystic Series comes in eight colors, each with dark foliage. At about half the height of most varieties, they are much more manageable in a small space than so many dahlias.
Photo: Rob Cardillo