McCreary: Plant by May Day for dahlias in July
To more seasoned gardeners, there’s no mystery at all. They know exactly what each bulb, corm and tuber requires to produce lavish blooms and they go to great lengths to nurture them. Tulip lovers dig up old bulbs and replant with fresh ones every year, or are sure to buy perennial species that are genetically primed to rebloom annually.
Anyone who gardens by the book carefully separates old gladiolus corms from the new, keeps summer irrigation water away from naked ladies (Amaryllis belladonna) and divides irises every year or two to avoid overcrowding.
Serious dahlia growers treat tubers with similar care. They plant on schedule in spring, fertilize regularly until late summer, strip foliage and flowers from spent stems in late fall, dig up clumps before cold weather and heavy rains begin, divide clumps, label, and treat with fungicide or a mild bleach solution.
The rest of us carry the memory of beautiful dahlias in the garden and in bouquets until the next year when we hope to find them flowering once again. No wonder their appearance seems like a miracle.
Growing dahlias as long-lasting perennials doesn’t have to be as rigorous and labor-intensive as some gardeners make it, but results pay off when you give tubers a little extra attention.
[SUBHEAD_RAG_]Dividing tubers
Although dahlias survive if left in place, they are better protected when dug annually, especially if planted in heavy soil. Cold, soggy conditions promote rot and spell the end of fleshy tubers, but not if they’re wrapped in newspapers and/or vermiculite, dry sand, peat moss, or sawdust, and stored in a cool, dry place.
After digging in late fall, an alternative treatment to dividing clumps immediately leaves them intact to wait until spring before separating tubers. This approach has one distinct advantage. In spring, as stored tubers begin to sprout, it’s easy to see where to make divisions.
Each tuber must contain an “eye” at the top similar to a potato in order to grow into a new plant. These eyes are only at the top but can be difficult to discern when tubers are completely dormant, but they’re clearly visible after sprouting.
When stems and tiny leaves begin to show themselves, divide clumps into single sections with one eye per tuber.
In loose, well-drained soil in a warm microclimate, it’s possible to leave clumps in the ground over winter and dig and divide them every other year. If you left some in the ground last year, you can still dig and divide now. Remove any rotted pieces and let cut areas heal over before replanting.
[SUBHEAD_RAG_]Potting up
Some gardeners like to pot up tubers and wait for several inches of growth before setting them out in garden beds on May Day or by May 15.
If you don’t have light, rich, fast-draining soil, it’s advisable to add plenty of compost. In areas of heavy clay, it may help to mix small lava rock or perlite into the planting hole as well. Sunny sites are best, but some afternoon shade is tolerated.
[SUBHEAD_RAG_]Planting and staking
All but the smallest dahlias benefit from staking, which should be a part of the planting routine. Stakes added later when blossoms become too heavy to be held aloft can easily puncture tubers.
The recommended procedure is to excavate an elongated hole, insert a stake in center — 5 feet high for the tallest dahlias — lay tubers on their sides, and cover with 3 inches of soil. The eye should point upwards and lie about 2 inches from the stake. As stems elongate, loop twine around at intervals and tie to support.
For bushy plants, nip off the top bud after three or four sets of leaves form or after five to seven sets of leaves on smaller varieties. Side branches will produce three flower buds, but remove side buds in favor of larger terminal blossoms.
[SUBHEAD_RAG_]Enjoying cut flowers
Dahlias make excellent cut flowers and complement nearly any type of bouquet. Blossom types range from flat and single to many-petaled balls; from loose-petaled cactus and dinner plate types to tiny pompons; and they come in nearly every color except blue.
The more that flowers are cut and faded ones deadheaded, the more abundant the blossoms.
Rosemary McCreary, a Sonoma County gardener, gardening teacher and author, writes the weekly Homegrown column for The Press Democrat. Write to her at P.O. Box 910, Santa Rosa, 95402; or send fax to 664-9476.