Known for its vibrant colors and tightly-packed (often large) flower heads, the Dahlia is truly a wonder to behold in the summer garden. In this article, we’ll review the advantages of using these beauties in your garden, as well as different planting techniques and tips for growing them.
Dahlias come in a wide range of shapes, sizes, and colors. The two largest classification of dahlias refer to the petal arrangement. These classifications are single-flowering (typically grow less than 3′ in height and blooms tend to be less than 4″ in diameter) and double-flowering (typically grow in excess of 3′ in height and forms larger blooms). The single-flowering dahlias include the Impression, Single, Orchid-Flowering, and Collarett varieties and tend to be less popular. The double-flowering dahlias consist of the Cactus, Semi-Cactus, Decorative, Dinnerplate, Ball or Pompon, Border, and Novelty varieties. The terms “single-” or “double-“flowering does not refer to how many times the plant will bloom but rather to the bloom structure itself. The single-flowering varieties bloom with just a single row of petals where as the double-flowering will have multiple rows.
When purchased as bulbs, Dahlias are sold as “tubers”. These tubers often resemble somewhat of a disfigured hand with multiple “fingers” extending downward from the center. The center of this tuber is actually the crown of the stem from the previous year’s growth! When this dahlia begins to sprout after planting, you will be able to see small green shoot protruding from this center crown. Like most bulbs, Dahlias require a well-drained soil (a good mixture of organic material including peat moss and compost manure does wonders) with little clay content. Again, like most bulbs, the Dahlia tubers will surely rot if allowed to sit wet for long spans of time. Select a location that is quite sunny (receives at least 6 hours of sunlight per day) and protected from strong winds. The tubers should be planted “fingers down” in the soil, with the center of the tuber where the stem was the year before just at the soil surface. Depending on the size of the tuber and the specific dahlia variety, spacing should typically range from 18-36″ apart, leaving them enough room to spread and grow properly.
As previously mentioned, Dahlias should be planted during the spring season, anytime after the threat of frost is gone but before the weather gets too warm. For most of the United States, this time period falls between mid-March and mid-May. Dahlias will
begin blooming mid-summer and most will continue on in the late summer and sometimes early fall! Keep the soil moist but definitely not saturated during the summer months. Once the plants reach a foot or so in height, the terminal shoot (or center stem) of the plant can pinched back to encourage branching. For increased flower size, pinch back the lateral (side) flower buds to direct more energy and nutrients to the main flower bud at the end of the stem. Fertilize once per month during the growing season with a water soluble fertilizer (such as Miracle-Grow).
Once the plants have completed their growing and blooming cycle, the leaves and flower stems will begin to die back as they enter their dormant stage. Dahlias are hardy in Zones 8, 9, 10, and 11. In these areas, simply cut the stems back to with 1-4″ of the soil surface once they have completely died back. Leave the tuber in the ground for the remaining fall and winter. If located in zones north of Zone 8 (Zones 1-7), you will need to take special care of the tubers in order to protect them from the harsh winter weather. Southern parts of Zone 7 can usually get away with giving the tubers a good drink of water in the fall and placing a think layer of mulch over the area where the tubers are planted. To be really sure, however, the tubers will need to be removed from the soil and overwintered indoors. To do so, follow these simple steps:
- After the first frost, cut back the foliage and stems to within 1-4″ of the soil surface.
- Carefully dig out the dahlia tuber, being sure not to sever any of the “fingers”. In order to avoid this, begin by digging at least 12″ away from the center of the plant in all directions.
- Gently brush off any excess dirt from the tubers and spread them out in a shaded, well-ventilated area for several days. Do NOT leave the tubers in full sun.
- Pack the tubers upside down in a well-ventilated box, basket, or bag using slightly damp vermiculite, perlite or peat moss, covering the clumps of tubers.
- Store in temperatures of 35°F to 50°F and protect from hot or cold drafts.
- Replant in the spring once ground has thawed.
One of the longest summer blooming bulbs, the variety and vibrant colors of Dahlias are something you won’t want to leave out of your summer garden this year. Whether you’re a veteran gardener or just starting to get your hands dirty, these tubers are sure to please without much fuss. Looking great in the garden as well as in a large vase on your dining room table, try some this year and be the talk of the town!
Until next time,