Designing Gardens with Plant Height: Scale and Layering Techniques

Choose Plants in Scale

Select plants that relate to surrounding structures. If a bed borders a 4-foot fence, choose plants that reach slightly above the posts. If they stop short, the fence dominates and cages the planting. Once you set the tallest plant, step down heights by roughly half: underplant a 6-foot canna with a 3-foot zinnia, then an 18-inch ageratum or Gomphrena. For a taller backdrop, add a castor bean or sunflower behind the canna.

Without a structure, let the tallest plant equal half the bed's width. Around a birdbath or sculpture, plants should be no more than two-thirds the object's height. At the garden center, stage large specimens side-by-side to visualize scale—you can still buy smaller plants to save money.

If you misjudge scale (e.g., a tall banana with creeping verbena), the look may be cartoonish. Fix it by adding mid-sized plants between them. Mistakes with arbors or sculptures are less forgiving: too large overwhelms plantings; too small gets lost.

Trailers as Groundcovers

For ground coverage, consider trailing plants. They cascade beautifully from containers and form colorful carpets in beds. Good choices: spreading petunia (Wave series), Bidens, creeping zinnia, purple heart.

Size It Up

Quick-reference annuals and tender perennials for tall, medium, and short layers:

Tall (48–72 inches)

• Angel's trumpet
• 'Mahogany Splendor' hibiscus
• Sunflower
• Castor bean
• Ornamental millet

Medium (18–48 inches)

• Cleome
• Coleus
• Magilla Perilla
• Blue anise sage
• Zinnia

Short (4–18 inches)

• Impatiens
• Petunia
• Vinca
• Ageratum
• Creeping zinnia