Take three simple species from Mexico, let plant breeders in Europe go nuts with them for a couple of centuries, and what do you get?
Hundreds, if not thousands, of different dahlias bearing showy, summertime flowers ranging in size from a half dollar to a dinner plate, in nearly every shade of the rainbow except pure black.
And that diversity doesn’t include the myriad shapes that the petals take, from cactus to peony to pompom to water lily. In all, the American Dahlia Society lists 20 different classifications just based on the petals, along with nine sizes and 15 colors.
As to why the many choices: dahlias are “natural hybrids,” meaning that from seed, the offspring rarely look like their parents. Instead, they shift color and change form at whim.
Hybridizers have capitalized on this trait and are constantly concocting new varieties, some intentional and others not. Then, when the hybridizers have achieved a dahlia that they’d like to reproduce, they replicate it by taking cuttings, snapping off tubers, or harvesting tissue to clone in laboratories.
How to Choose?
With their improbably perfect flowers, dahlias are just about impossible to resist.
The greatest challenge may be in deciding whether to grow them for their sparkling colors in the garden, as cheery, cut flowers to bring indoors, as “show blooms” to impress family and friends, or to enter in contests.
Depending on your preferences, there are several ways you can grow them.
Dahlias grow from fat, swollen roots called tubers, which look somewhat like small, lumpy sweet potatoes.
Plant those tubers over the next month, and they’ll take off, quickly pushing up new stalks through the earth, leafing out and bearing amazing blooms by summer. In late fall to early winter, they’ll drop their leaves and die back to the ground, storing their energy until the following spring, to begin the cycle anew.
Or you can wait another month or two, until local nurseries offer bedding types already up and growing in pony packs and 4-inch pots.
However, that means that you’ll be limited to a narrow selection. If you’re at all tempted by the many spectacular varieties offered by specialty growers, you’ll most likely need to go the tuber route.
Or you can split the difference and order your dahlias from a nursery like Corralitos Gardens, a grower near Monterey that sells more than 200 varieties of small, new plants. The tubers are already rooted, and up and growing. So there’s no waiting to see whether your tubers will take.
Regardless of whether they’re planted as tubers or sprouts, all dahlias need plenty of sunlight, excellent drainage and fertile soil. Think vegetable-growing conditions. Indeed, the American Dahlia Society states on its web site, “If you can grow tomatoes in your garden, you can successfully grow dahlias.”
For tubers, dig a hole 1 foot deep and 1 foot wide for each. Spacing, in general, matches height. For example, 3-foot tall dahlias should be planted 3 feet apart. You can squeeze them closer together. However, dahlias are susceptible to mildew, and one of the best ways to combat the disease is to provide space for air to circulate between the plants.
Mix the excavated soil with potting soil, well-rotted chicken manure, compost or other medium-textured, organic material, along with a handful of bone meal. Put 4 inches of mix into the hole, then lay the tuber flat on top. Make sure its eye — the small, flat circle where new growth will sprout — is pointing up.
Next, for taller dahlias, drive in a sturdy, 4 to 6-foot tall redwood stake or rebar about 6 inches from the tuber. If you pound in the stake later, you may pierce the tuber and kill the plant.
Cover the tuber with a few inches of the planting mix and water thoroughly. Don’t water again until you see sprouts. Once the dahlia is up several inches, add a couple inches of the planting mix. Chase the plant with the mix as the plant grows taller. But don’t bury it. You’re done when you’ve filled the hole.
Shape a basin around each plant, or set up soaker hose or drip irrigation for watering. Mulch with a couple of inches of loose, organic material, such as shredded bark, to retain moisture.
You can bypass most of these steps if you plant actual plants. However, still amend the top foot of soil, shape a watering basin or set up irrigation, and mulch. Water thoroughly the first day, then every other day for the rest of the week. After that, water about once a week.
When your dahlias reach 6 to 8 inches tall and have three to four sets of leaves, you can start fertilizing. For quick results, use a liquid solution about once a month through September. Apply a high-nitrogen fertilizer at the outset, then back off the nitrogen by the middle of summer.
Dahlias like a deep soak about once a week. If your soil is sandy, you may need to water every three to five days; in heavy soils, the interval may stretch to 10 days. Also, taller plants need more water.
During summer heat, your plants may wilt slightly in the afternoon. If the leaves perk up in the evening, don’t alter your watering schedule. If the leaves stay wilted, increase the frequency.
Dahlias don’t like overhead irrigation. But if aphids appear, you can evict the soft-bodied insects by blasting them with water from a brass hose nozzle.
Whether harvesting dahlias for bouquets or simply deadheading, think in threes. That is, dahlias bloom in clusters of threes, with a center flower and a matching one emerging from each side. Let all three bloom if you want lots of flowers. Or remove the side buds to force a bigger center flower. Whichever approach, once those three buds are done, make your cut lower on the stem, just above the next set of three.
At the End of the SeasonIf your dahlias decline at the end of summer, whack them to the ground and keep watering. The plants may send up new branches and resume blooming in October and November.
Some folks dig up their tubers for winter. In areas where the ground freezes, that’s a necessity. However, on the Central Coast, it’s fine to leave them in the ground.
Over time, your dahlia tubers will increase in mass. After three to four years, lift the dormant tubers during winter. Snap off any succulent tubers bearing at least one eye to create new plants. Discard any tubers that are shriveled, light in weight or lack an eye. Replant the viable tubers by following the steps for any new tuber, and you’ll be on your way to ever more dahlias.
Harvesting Dahlias for Bouquets
With their thick, succulent petals and thick, succulent stems, you’d think that dahlias would be long-lasting cut flowers.
Not so, unless you flame them first.
• Prepare a pot of nearly boiling water.
• Dissolve some floral preservative in it.
• Recut the stems.
• Dip the tips in the super-hot water for 20 to 30 seconds, holding the stems at an angle so the steam doesn’t wilt the flowers.
• Plunge the stems into a vase, which you’ve already filled with cool water.
By searing the stems, your cut dahlias should last a week. Otherwise, they may expire after only a day or two. Unfortunately, the conditioning technique is a one-time trick. Cutting the stems and dipping again a week later won’t prolong the bouquet.
Seeds of Wisdom
Go ahead and buy dahlia tubers this month and next. But wait to plant them if the ground is sopping wet, as they can decay in cold, wet soil.
2357 Lemur Street
Santa Rosa, CA 95401
295 Alitos Drive
Corralitos, CA 95076
Swan Island Dahlias
PO Box 700
Canby, OR 97013
Visit Joan’s website at www.SantaBarbaraGardens.com, or post a comment by clicking on “Leave a Comment” back up at the top.