Impatiens are popular annual flowers for adding continuous color to shaded areas, including the standard bedding plant, Impatiens walleriana, and the larger New Guinea Impatiens. Achieving successful growth and abundant flower production depends on providing the correct amount of space between each plant. Proper spacing is the most important consideration after selecting an appropriate planting location.
Calculating Spacing Based on Impatiens Variety
The ideal distance between impatiens varies significantly depending on the specific type planted, as their mature sizes differ widely. Standard Impatiens walleriana, often called Busy Lizzie, are smaller and are typically planted close together to achieve a dense, carpet-like effect. These plants require a separation of 6 to 8 inches from center to center to allow for full, bushy growth and quick soil coverage.
New Guinea Impatiens (Impatiens hawkeri hybrids) are larger, featuring thicker stems, bigger leaves, and a wider mounding habit. These varieties require more room to reach their full potential. A minimum spacing of 12 inches is recommended for New Guinea types, with some vigorous cultivars benefiting from up to 18 inches of space between plants. This greater separation accounts for their larger spread, which can reach up to two feet wide for certain selections.
The Horticultural Rationale for Proper Spacing
Spacing measurements are based on the biological needs of the plant, especially concerning disease management. Crowding the foliage creates a humid microclimate that is highly favorable for the development and spread of fungal pathogens. The primary concern is Impatiens Downy Mildew, caused by the water mold Plasmopara obducens, which is particularly damaging to Impatiens walleriana.
When leaves overlap, air movement is restricted, preventing the foliage from drying quickly after rain or irrigation. This prolonged moisture creates the perfect environment for the pathogen’s spores to germinate and infect the plant tissue. Allowing sufficient space promotes air circulation, which hastens the drying of the leaves and significantly reduces the risk of this disease.
Adjusting Density for Containers and Mass Plantings
The spacing guidelines serve as a baseline, but they can be modified based on the desired visual impact and environment. In ground beds or mass plantings, the goal is often to achieve complete and uniform coverage quickly. Gardeners may plant I. walleriana at the closer end of the recommended range (around 6 inches apart), accepting a slightly higher disease risk for immediate visual density.
To determine the number of plants needed for a mass planting, first calculate the square footage of the area by multiplying the length by the width. Then, divide this square footage by the square of the desired spacing (e.g., 6 inches = 0.5 feet; 0.5 x 0.5 = 0.25 square feet per plant). For example, a 100-square-foot bed planted at 6-inch spacing would require 400 plants.
In contrast, container plantings such as hanging baskets, window boxes, and patio pots often require plants to be intentionally crowded to create an immediate, overflowing display. This technique trades long-term health and air circulation for instant aesthetic appeal. In a typical 16-inch container, one might plant five or six impatiens, a density far exceeding the landscape recommendation.
This high-density planting necessitates diligent cultural care to compensate for the close quarters. Watering must be precise, avoiding overhead methods that soak the foliage, and the soil must be well-draining to prevent root rot. Furthermore, the limited root space requires more frequent fertilization, as the numerous plants rapidly deplete the nutrients in the potting mix.