Zinnias and dahlias: two beautiful summer flowers
These 'cousins' make great cut flowers and brighten up the late season garden
October 01, 2009 | 04:40 AM
Zinnias and dahlias have always seemed very similar to me. Their big showy flowers, in a rainbow of colors, appear in summer and last until fall. Both need to be re-established each spring. Both are attractive to butterflies. And both are natives of the Southwest and Mexico. So, in my mind, they're sort of interchangeable.
I know that my observation is not really true, but I'm not the only one to see the similarity. Look at the two plants' scientific classifications — their entire lineage is the same, from Kingdom (plants) down to the order Asterales and family Asteraceae. Only their genus (zinnia and dahlia respectively) are different.
The main difference between these two groups of plants, as far as the gardener is concerned, is that zinnias are primarily annuals which grow from seed (frequently reseeding themselves in the garden) while dahlias are tender perennials which grow from tubers.
On Long Island dahlia tubers must either be lifted and saved each fall or you can treat them like annuals, leaving them in the ground to die and be replaced the following spring.
Knowing that both are natives of a milder climate should have immediately tipped you off to the fact that even the perennial dahlias won't survive outside over our winters.
I read once that dahlia culture is very similar to tomato culture. So, don't put your dahlias out too early or they will suffer from the cold. Do plant your dahlias in a sunny location. Interestingly, tomatoes were first grown in Mexico as well.
Another difference between zinnias and dahlias is that of flower shape. In looking at the zinnias, you'll notice that most of the flowers are more two dimensional, looking more like a plate while the dahlia flower tends to be more three dimensional, looking more like a ball of petals.
Dahlias have become extremely popular with gardeners in recent years. There are over 30 species and 20,000 cultivars. Dahlia flowers can be tiny, perhaps just two inches across or very large, up to a foot across. These large ones are sometimes referred to as "dinner plate" dahlias. Dahlia flowers can be single (like 'Bishop's Children') or double, in one color or bicolored ('Duet'). The petals range in shape from short and broad to long and narrow, some curling either inward or upward like 'Splash.' Both zinnias and dahlias can be dried for longlasting arrangements.
Like most very colorful flowers, both dahlias and zinnias prefer a sunny location and well-drained soil. Dahlias and zinnias also prefer an only mildly acidic soil, say 6.0 to 6.5. If your soil is like mine, much more acidic than that, you will need to add some lime to sweeten the soil.
While dahlias do produce seeds, they grow from tubers, so that if you do lift your dahlias from the ground in the fall you will notice that they have produced many more tubers for next year's flowers. Some dahlias are either sterile or producing seeds that will not breed true, so you're more likely to get more of what you started with if you propagate them vegitatively (from the tubers). On the other hand you may get a pleasant surprise growing the seeds.
To learn more about dahlias, go to the American Dahlia Society at www.dahlia.org or the Long Island Dahlia Society at www.longislanddahlia.com.
The Long Island Dahlia Society will host is fall dahlia show on Saturday, Oct. 3, from 1 to 5 pm and Sunday, Oct. 4, from 10 am to 5 pm in the Carriage House at Bayard Cutting Arboretum, Montauk Highway, East Islip.
For further information on the show, go to www.LongIslandDahlia.com or call 754-1002 after 8 pm or 516-832-3652 during the day.
Ellen Barcel is a freelance writer and master gardener. To reach Cornell Cooperative Extension and its Master Gardener Program, call 727-7850.