Calculate how many plants you need
Formula and example
Plants = bed area ÷ coverage per plant
Square-grid coverage is spacing × spacing. A triangular layout uses a 0.866 factor and places more plants in the same area.
At 18 inch spacing, each plant in a square grid covers 2.25 square feet. A 120 square foot bed needs 54 plants after rounding up. Adding 5 percent produces a suggested purchase of 57.
Plan the layout before buying
- Use the plant's expected mature width, not its nursery pot size.
- Subtract areas occupied by rocks, trees, structures and established plants.
- Set the first row an appropriate distance from hard edges and paths.
- Choose a staggered layout for a more natural fill, or a square grid for formal alignment.
Last updated August 28, 2026. Confirm mature spread, light, soil, moisture and hardiness requirements for each selected plant.