Zinnias are popular annual flowers, cherished for their vibrant colors and ability to bloom prolifically throughout the summer and fall. While they are relatively easy to grow, damage or disappearance of a healthy plant is often caused by common garden pests, ranging from small invertebrates to larger browsing mammals. Identifying the animal responsible is the first step toward implementing the correct control measure.
Identifying the Main Culprits and Their Damage Signature
The type of damage found on zinnias provides the best clue for identifying the culprit, as different animals have distinct feeding habits. Damage caused by rabbits is easily recognized by a clean, 45-degree angle cut on the stem or leaves, similar to a cut from sharp scissors. This feeding occurs close to the ground, usually within the first 18 inches of the plant, since rabbits cannot reach much higher.
Deer damage, in contrast, is characterized by a ragged, torn, or ripped appearance on the stems and leaves. Deer lack upper incisors, so they must grasp and yank the plant material, leaving behind a jagged edge. They can browse much higher up the plant than a rabbit. While zinnias are occasionally considered deer-resistant due to their coarse texture, a hungry deer will consume them, especially tender young growth.
If entire plants or large sections of foliage disappear rapidly, especially in gardens near fields or wooded edges, the culprit is likely a woodchuck, also known as a groundhog. These rodents are herbivores and can quickly mow down a bed of flowers, often leaving behind large burrow entrances nearby as a telltale sign. For smaller, irregular holes in the leaves that cross the veins, especially on new seedlings, look for slugs or snails. These mollusks leave a distinctive, shiny, silvery slime trail on the leaves, stems, or surrounding soil as they move across the surface at night.
Physical Exclusion Methods
Physical barriers are often the most reliable method for protecting zinnias because they completely block access to the plant material. Barrier specifications must be tailored to the animal’s physical capabilities, particularly height and digging strength. Deer fencing needs to be a minimum of eight feet high in open areas to be fully effective. However, in smaller garden plots or areas with uneven terrain, a seven-foot fence may provide a sufficient deterrent.
For rabbits and woodchucks, barriers must block access at ground level. A fence for these animals only needs to be two to three feet tall, but it must be made of wire mesh with openings no larger than one inch to prevent young animals from squeezing through. The bottom six to twelve inches of the fence must be buried in the ground to discourage digging under the barrier. The most effective installation involves bending the buried portion outward into an L-shaped apron, discouraging the animal from digging directly next to the fence line.
For protecting individual plants or small groupings, chicken wire cages or floating row covers can be used as temporary barriers. These covers work best on young zinnia seedlings, which are more vulnerable to damage from both mammals and insects. Against slugs and snails, a low-tech physical barrier can be constructed using a ring of copper sheeting placed around the plant base. Copper emits a small electrical charge when it contacts the slug’s mucous, creating a natural deterrent that prevents them from crossing the barrier.
Repellent Strategies and Environmental Deterrents
Repellents and habitat modification make the garden area unattractive or inaccessible to pests. Taste and scent repellents, often containing capsaicin, putrescent egg solids, or sulfur-based compounds, make zinnias unpalatable or signal a predator presence. These sprays must be reapplied frequently, especially after heavy rain, as the active ingredients wash off.
Companion planting uses the strong aromas of other plants to confuse or deter pests. Interspersing zinnias with herbs like mint, chives, or rosemary creates a powerful aromatic barrier that can mask the smell of the flowers, making it harder for herbivores to locate their intended meal. Some plants, such as marigolds, are also thought to act as trap crops, attracting certain pests like aphids away from the more desirable zinnias.
Modifying the garden environment can greatly reduce the population of smaller pests like slugs and snails. These creatures thrive in cool, dark, and damp conditions, so removing debris, leaf litter, and woodpiles near the garden eliminates their preferred daytime hiding spots. Adjusting watering practices is also an effective cultural control. Watering early in the morning allows the sun to dry the zinnia foliage and soil surface before evening, minimizing the damp conditions that slugs and snails need to feed and move around.