Zinnias are favored by growers because of their vibrant colors and exceptional productivity throughout the summer. Growing zinnias specifically for the cut flower market requires a different approach than simply adding a few colorful plants to a landscape border. This guide focuses on the tailored techniques necessary to achieve the long, straight stems and high-quality blooms that ensure a successful vase life. By adjusting planting density and implementing specialized maintenance practices, growers can transform this easy-to-grow flower into a high-performance cutting crop.
Choosing Varieties and Preparing the Site
Not all zinnias are suitable for cutting; many popular bedding varieties are bred to be short and bushy for landscape aesthetics. For cut flower production, growers should select tall, sturdy series engineered for stem length and disease resistance, such as the Benary’s Giant or State Fair series. These specific varieties naturally produce long, thick stems that support large flower heads. The Queen Lime series offers unique, muted color tones while maintaining the necessary stem structure, expanding the palette for designers.
Zinnias demand a location that receives a minimum of eight hours of direct sunlight daily to fuel their rapid growth. Insufficient light results in weak, spindly stems and reduced flower production. The soil must be well-draining, as these plants are susceptible to root rot in waterlogged conditions. Incorporating generous amounts of well-aged compost or other organic matter before planting improves soil structure and provides the initial nutrient base.
Planting and Initial Establishment
Zinnias are sensitive to cold temperatures and should only be sown directly into the prepared garden bed after all danger of frost has passed. While they can be started indoors three to four weeks before the last frost, direct sowing is preferred because zinnia seedlings can be temperamental when transplanted. If starting seeds indoors, use biodegradable pots to minimize root disturbance when moving them outside.
Planting seeds closer together than traditional garden spacing, typically between six and nine inches apart, forces the young plants to compete for light. This encourages them to grow taller and straighter rather than branching out sideways. During the early establishment phase, consistent moisture supports germination and rapid root development. Once established, reduce watering frequency but ensure the soil is deeply saturated when irrigation is applied.
Specialized Growing Techniques to Maximize Production
To maximize the number of usable stems per plant, growers must “pinch” the main growing tip when the plant reaches approximately 12 to 18 inches in height and has developed three to five sets of true leaves. Pinching involves removing the central stem above a healthy set of leaves. This action redirects the plant’s energy toward developing strong lateral side shoots, resulting in a bushier plant that produces multiple long stems suitable for cutting instead of just one main flower.
Tall zinnia varieties, especially those with heavy blooms, require structural support to prevent wind damage and ensure the stems grow perfectly straight. The most effective method is using horizontal netting stretched tightly across the growing area at two different heights. As the plants grow, they push through the netting, which provides gentle resistance that keeps the stems upright and prevents them from bending or kinking.
Since zinnias are continuously harvested, they require a steady supply of nutrients to support their production cycle. A consistent feeding regimen with a balanced, water-soluble fertilizer applied every two to three weeks replenishes nutrients removed during harvesting. Deep, less frequent watering encourages the development of deep, robust root systems. Allowing the top inch of soil to dry out slightly between these deep watering sessions helps to prevent fungal issues like powdery mildew.
Harvesting and Conditioning for Vase Life
The timing of harvest is important for achieving a long vase life, and the bloom must pass the “wiggle test” before cutting. To perform this test, gently grasp the stem about six inches below the flower head and lightly shake it. If the flower head flops or nods freely, it is too immature and will likely suffer from “bent neck” once placed in a vase. The stem is ready for cutting only when it feels stiff and the flower head remains firm and stable during the wiggle test.
The best time to harvest zinnias is during the cooler parts of the day, either early morning after the dew has dried or late in the evening. When cutting, make the incision high on the plant, just above a set of healthy leaves or a developing side shoot, which encourages rapid regeneration of new flowering stems. Immediately after cutting, the stems should be plunged into a clean bucket of cool water that contains a commercial floral preservative solution.
Before placing the flowers in the conditioning solution, strip all foliage that would sit below the water line, as submerged leaves quickly decompose and introduce bacteria that shorten vase life. Allowing the newly cut flowers to hydrate in a cool, dark location for several hours is a conditioning step that significantly extends their longevity. With proper harvesting and conditioning, zinnias can reliably provide a vase life of seven to ten days.