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Growing Dahlias

It was a sad day in May of 1988 when Dr. Charles Mayo, a whale biologist living in Provincetown, Massachusetts, planted his first dahlia. Dr. Mayo (known as Stormy to his friends) had just returned from the hospital where his young wife had died of breast cancer. His wife had been the gardener in the family, and Stormy hadn't paid much attention to her plants. But he knew she hadn't been able to plant her dahlia tubers that year, so he found them in the basement, and went outside and planted them.

Since then dahlias have become a hobby that borders on being an obsession. His front yard no longer has grass. It is just row upon row of dahlias - over 80 different varieties. I met him one day last fall, and he shared some of his knowledge with me.

Dahlias are definitely bodacious. The blossoms are large -generally from four to twelve inches - and full of colorful rays that just burst with color. The spectrum of dahlia colors in Dr. Mayo's yard begins with cool yellows, advances to rich lemon, and on to orange. Others are pink, red, rose or magenta. Many will mix and blend two or more colors in a single blossom, Tropic Sun, for example, has both peach and lemon in each gorgeous six-inch blossom. Lauren Michelle has pink with purple. Santa Claus? You guessed it, red and white.

Dr. Mayo plants his dahlia tubers each spring as soon as the soil has warmed up - it needs to be at least 50 degrees, and preferably 60. He plants them sideways about 6 inches beneath the surface of the soil. He adds some fertilizer to the soil each year, rototilling it in before planting.

I called Swan Island Dahlias (www.dahlias.com or 800-410-6540) and talked to Jennifer Gitts-Eubanks, a third generation member of the business. She suggested adding a handful of bone meal to planting holes - for added phosphorus. She also noted that using nitrogen rich, fast-acting chemical fertilizers would produce huge plants- but few blooms. Bagged cow manure added to the planting hole is good, she said, and all that is really necessary.

Good drainage is important. Part of Stormy's success is due to the soil of Cape Cod - sandy and fast draining. For heavy soils, it is best to dig a large hole, and mix in plenty of composted manure or compost. Neutral pH is best, in the range of 6.5 to 7.0. Full sun is important - eight hours is ideal.

For those of us in northern New England, dahlias generally don't bloom until late August or early September. There are a few early dahlias that bloom 75 days from planting, but the biggest, juiciest ones take 120 days, and most take at least 90 days.

So what can we do? I'm going to order some tubers now, and plant them indoors in pots. I'll aim to plant them 6 weeks before last frost day, say April 15. I'll use a cheap plastic pot that I can slice open without disturbing the roots at planting time. The perfect size for transplanting is when the stems are about 12 inches tall, Gitts-Eubanks told me. She also told me to pinch back the stems when the plants have three sets of side leaves to produce stockier, more floriferous plants. And later, when they bloom, keep on cutting the flowers - or they'll stop.

Most dahlias are tall, so Stormy sets a 1-inch hardwood stake by each of his at planting time. He applies a splotch of white paint to each stake, then writes the name with a black marker. He ties the stems on as they grow to their full height of 3-5 feet.

In the fall you must dig up your tubers as they are not cold hardy. Dr. Mayo advises letting the frost kill the leaves, then digging up the tubers 2-3 weeks later. He washes his, and writes the name of each variety on plastic surveyor's tape that he ties around the tubers. He lets them dry out a little, then packs them in damp cedar chips in cardboard boxes. The ideal temperature for storage is 40 degrees, he told me.

Dahlias, in my experience, are relatively problem free. In fact, the only pests on mine have been earwigs, which I occasionally shake out of the blossoms when cutting them for arrangements. But Dr. Mayo has, essentially, a monoculture - and monocultures are prone to problems. So it is not surprising to me that he does have insect and fungal pests from time to time. Dahlias are a bit like cats - unspayed barn cats, that is. A single tuber planted in spring will yield several by fall. In the spring you can divide a big clump with a sharp knife and get several smaller clumps that will bloom well that year, and make even more by summer's end. So you will need to constantly keep on expanding the domain of your dahlias - or start giving them away.

Michael Fuerst of Cornish Flat has been giving away tubers of a dark red dahlia for years, so everyone in the village has it. But now that I've seen Stormy Mayo's dahlias, I'm ordering some new varieties - and will pass them along in future years.

Henry Homeyer is the VT/NH associate editor of People, Places and Plants magazine. His website is www.gardening-guy.com.