The decision on how far apart to space your plants might seem straightforward when buying at a garden center. You may be able to fit three perennials in a single planting hole; a shrub sits snugly inside its container; and a plant fills only a small portion of its pot. But, when these plants mature, the planting can look overcrowded and clumped together. Pot size represents what a plant currently looks like. However, we need to design our gardens with what the plant will look like in the future in mind.
While mature height is often considered, mature spread can be just as critical. A wide-spreading shrub can encroach into other plant groups and cover a groundcover or fill in the negative space between different plant forms. Moreover, two plants may reach the same height but occupy vastly different areas in the bed. A tall, upright plant takes up less space than a round plant that reaches the same height. Considering both dimensions allows us to envision the final look of the bed.
This consideration is particularly relevant when designing layered plantings. A low-growing plant might appear to have ample separation from a taller, mid-layered plant in a new bed. Yet, plants in the back may become wide and spread forward or droop down, obscuring the foreground. A tall shrub may also obscure nearby plants if its mature spread isn’t considered. We shouldn’t just think about the footprint of each plant, we should consider how large each plant will grow. The key is to give each plant enough room to fill out without forcing them to form a mass.
Leaving enough space between plants might seem daunting, particularly in a new planting. A young bed might look too barren or the bare soil might invite you to add more plants right away. Adding more plants might look good in the short term, but it could lead to problems down the line. Repeating plants and creating a rhythmic pattern doesn’t mean they must touch one another from the start. Bare spots in the soil can act as buffers between plant groups, accentuate contrasting leaf textures, and allow focal points to shine.
An effective way to consider plant spread is to draw a rough sketch of the bed and size each plant according to its mature spread. If a plant is expected to get three times as wide, draw a circle that is three times as wide as the current pot. Then, sketch each plant’s projected size in the drawing and see where the circles overlap. Some overlap is perfectly acceptable within a soft perennial grouping, but too much overlap might indicate that the bed is designed for year one rather than years two to ten.
When we can see beyond the empty spaces of a current planting, we gain a better idea of what the space will look like in the future. Considering plant spread allows us to estimate spacing, plant mass, visibility, and balance ahead of time. If each plant group has ample room to expand into and adjacent groups still look distinct, the design will have a robust foundation for the coming years.
