Grouping plants, often called massing, is a foundational technique in landscape design. It involves arranging multiple plants of the same or different species together to form a unified visual unit. This approach creates designs that look intentional, cohesive, and professionally executed. Designing with groups is also a practical strategy for reducing long-term maintenance requirements. Plant masses help suppress weed growth by shading the soil surface and promoting a healthier microclimate. Understanding how to group plants is the first step toward developing a resilient and aesthetically pleasing outdoor space.
Grouping by Shared Environmental Needs
The initial consideration for any successful plant grouping is the shared cultural requirements of the species being combined. Ignoring these needs leads to increased plant stress, higher maintenance burdens, and eventual failure of the planting bed. Matching plants based on their tolerance levels is a prerequisite for survival before any aesthetic concerns are addressed.
Begin by assessing the light exposure of the area, differentiating between full sun, partial shade, and deep shade locations. For example, a sun-loving perennial will struggle if grouped with shade-tolerant ferns beneath a dense tree canopy. Similarly, grouping drought-tolerant plants with moisture-loving species forces a difficult irrigation choice that will harm one group or the other.
Soil conditions also dictate which plants can thrive together within a mass planting. Plants sharing a group should have similar requirements for soil pH, drainage rate, and organic matter content. Acid-loving plants like rhododendrons must be grouped separately from those that prefer neutral or alkaline soils to ensure proper nutrient uptake and prevent chlorosis.
Arranging Plants by Height and Structure
Once plants are grouped by compatibility, the next step is arranging them spatially to create visual depth and ensure all specimens are visible. This involves creating vertical layers that mimic natural plant communities, a technique often described as feathering or staggering.
Background Layer
The tallest plants should form the background layer, typically consisting of upright shrubs, small trees, or large ornamental grasses. These provide a permanent structural backdrop.
Middle Ground Layer
This layer is populated with plants of intermediate height, such as medium-sized perennials and subshrubs, placed directly in front of the background. This zone provides the bulk of seasonal color and texture, serving as the transition between the permanent structure and the low elements in front. Plants here should partially overlap the base of the background plants, blurring the lines between the layers.
Foreground Layer
The foreground or edging layer consists of the shortest plants, including groundcovers, low-mounding perennials, and bedding annuals. This layer is positioned at the very front of the planting bed, often spilling over the edge to soften hard landscaping lines like walkways or retaining walls. Varying the shapes within the groups, such as placing pyramidal forms adjacent to mounding structures, prevents the planting from appearing blocky or overly uniform.
Principles of Massing and Repetition
Plant massing uses multiple individuals of the same species in a single, cohesive group to create a significant visual impact. A group of three to five plants creates a bolder statement than isolated individuals scattered across a large area. The dense foliage canopy of a mass planting also helps suppress weed seed germination by blocking sunlight from reaching the soil surface.
The “rule of odds” is a fundamental principle in massing, suggesting that plants should be grouped in odd numbers (e.g., three, five, or seven). Groups with an odd number of elements are perceived as more natural and dynamic than groups with an even number, which tend to look static. The exact number used depends on the scale of the landscape; larger areas necessitate larger groups to maintain proportion.
Repetition involves using the same plant species or grouping pattern multiple times throughout a landscape. Repeating a distinct group of specific perennials, for example, guides the eye through the space and creates a sense of rhythm and continuity. This repetition unifies disparate sections of the landscape, making the entire design feel more intentional and organized.
Creating Visual Interest with Color and Texture
After establishing the structural layers and group quantity, the final consideration is the aesthetic contrast and harmony within the masses. Texture refers to the visual coarseness or fineness of the foliage and is a powerful tool for differentiation. Grouping plants with fine, delicate leaves (e.g., ornamental grasses) next to plants with coarse, broad foliage (e.g., hostas) causes each plant to stand out more sharply.
Color can be applied using schemes that create either harmony or excitement. Harmonious schemes use analogous colors, which are adjacent on the color wheel (e.g., yellow and orange flowers), to produce a calm, flowing effect. Conversely, complementary colors, which are opposite on the color wheel (e.g., purple and yellow), create high contrast and draw immediate attention.
While flower color provides seasonal highlights, foliage color offers year-round visual interest not dependent on bloom cycles. Grouping plants with distinct foliage hues, such as silver-leaved lamb’s ears next to burgundy-leafed heuchera, sustains interest even when the plants are not flowering. These permanent color contrasts are applied within the established structural groups to ensure the design remains captivating across all seasons.