Dahlias are among the most popular garden flowers, prized for their dramatic, late-season blooms that showcase an incredible variety of colors and forms. These impressive plants can grow from compact bedding varieties to towering specimens reaching six feet or more in height. While their size contributes to their visual appeal, it also introduces a structural challenge that many gardeners encounter. For most varieties, the answer to whether they need support is a definitive yes, especially to protect their magnificent flowers from damage.
Why Support is Essential
The necessity of supporting dahlias stems from their physical structure and the sheer weight of their flowers. Dahlia stems, even when thick, often have a hollow or brittle core, making them susceptible to snapping under stress. This structural weakness means the plant lacks the internal rigidity to hold itself upright as it matures.
The primary stress factor is the immense size and weight of the blooms. Large varieties, such as the dinner plate types, can produce heads over 10 inches in diameter. When these blooms become saturated with rain or heavy dew, their weight increases significantly, applying leverage that can cause the stem to bend or break. Strong winds or sudden storms further compound this vulnerability, easily tearing stalks away from the plant’s base.
Determining Support Needs by Variety
The level of support a dahlia requires is proportional to its size classification. Dwarf or border varieties, which mature at less than two feet tall, generally possess a stockier, self-supporting habit. These smaller plants often require little to no staking, making them ideal for container gardening or the front of a garden bed.
Medium and tall varieties, especially those exceeding three feet in height, demand a reliable support system. The American Dahlia Society recognizes multiple bloom sizes, with ‘A’ (Large, 8–10 inches) and ‘AA’ (Giant, over 10 inches) varieties requiring the most substantial staking. If a dahlia is expected to grow taller than 36 inches or produces large flowers, a dedicated support structure is recommended to ensure the plant’s integrity throughout the season.
Practical Methods for Staking and Caging
Several reliable techniques exist to provide structural assistance, depending on the number of plants and their arrangement.
Single Staking
For individual plants or those scattered in a mixed border, single staking is effective. This involves driving a sturdy wooden or metal stake, typically five to six feet long, deep into the ground next to the plant. The main stem is then secured to the stake at 12 to 18-inch intervals using soft garden twine or flexible ties. Ensure a loose loop is maintained around the stem to prevent constriction as it thickens.
Corral or Perimeter System
When growing dahlias in rows or large beds, a corral or perimeter system efficiently supports multiple plants. This method uses tall, durable stakes placed at the corners and every three to four feet along the row’s edges. Garden twine is run horizontally between the stakes, creating a tight boundary. As the dahlias grow, additional layers of twine are added every 12 inches up the stakes, creating a supportive mesh that guides the stems upward.
Horticultural Netting
For very large patches or cutting gardens, horticultural netting stretched horizontally over the bed provides mass support. Sturdy posts are placed around the perimeter, and plastic mesh netting with a four to six-inch grid is stretched taut and secured to the posts. The dahlias grow up through the grid openings, which naturally supports the stems and branches from all sides. Heavy-duty tomato cages can also be used for individual, bushy plants, provided the cage height is matched to the expected mature height of the variety.
Timing and Placement of Supports
The timing of support installation is important, as waiting until the plant is large risks damaging the underground tuber system. Supports should ideally be placed when planting the tuber, or shortly thereafter, before the plant reaches 12 inches in height. Installing stakes early prevents accidental puncture of the brittle tubers, which can easily occur when driving stakes into the ground later.
The correct placement involves driving the stake three to eight inches away from the central planting point. This distance ensures the stake supports the main stem while allowing room for the tuber cluster to expand without being pierced. Once the support is in place, ongoing maintenance is required; the main stem should be secured to the stake every 12 to 18 inches as it gains height. Securing the plant progressively throughout the season protects the stems before the weight of the foliage and blooms becomes an issue.