Article by Patricia Matteson
Why: I want to find a perennial to plant through a freesia bed that is nothing but unsightly dry leaves from April to November. Preferably something with the opposite growing/flowering season. The plants must be low, because they will be growing below an espaliered cherry tree. I decided to research dahlias, in part because I know that they come in a wide variety of sizes, but mainly because I planted a couple of dahlias at the back of our garden many years ago, and I seemed to recall that they died back to ground level in late fall.
Scientific and common names, family: Dahlia spp., dahlias, family Asteraceae.
Type: Bushy perennial herb growing from a tuber. My memory served me well: perennial cultivars sprout in early spring and flower from midsummer to the end of the season, after which they enter dormancy.
Zone: Sunset Zones 1-24, USDA plant hardiness zones 8 and above (Suisun City is 9b). Dahlias are not frost-hardy. Plant in early spring when all chance of frost is past. Planting the tubers 4-6 inches deep provides some frost protection. Pots are OK. Dahlias need good drainage and part-to full sun. Tubers should be planted 1-2 feet apart, depending on the size of the plant, with the “eye” facing up. They flower best with liberal fertilization containing lots of phosphorus and relatively little nitrogen (10-30-20 is good).
Description: Flowers run from small to huge and showy (2-12 inches in diameter), and come in many shapes and almost every color except blue. Most have no scent. Depending on the cultivar, plants can grow up to 8 feet tall. Tall plants should be supported with a stake or a tomato cage. “Border dahlias” are 12-18 inches tall, and don’t need support. Royal Horticultural Society terms: ‘Dwarf Bedder (DwB)’ is less than 24 inches tall, ‘Liliput (Lil)’ is less than 12 inches. Pinch extensively at nodes to stimulate bushier growth and flowering, and deadhead the flowers.
Location: One sees dahlias everywhere, including as cut flowers for sale. Most recently, I visited the gorgeous dahlia garden at the Mendocino Coast Botanical Garden, just south of Fort Bragg. It was inspirational!
Pests and diseases: Snails and slugs will be a problem in my garden. I’ll be liberal with an iron phosphate-based molluscicide and hope the plants don’t sustain too much damage. Insecticidal soap is recommended for general use.
Conclusions for my garden: Border dahlias (the shorter plants) look like good candidates for a relay effect in the freesia bed: freesias sprout in winter, flower in very early spring, and go dormant shortly after that, whereas dahlias sprout in spring and flower until winter. So, I’ve decided try dahlias for relay planting.