Plant Spacing Calculator & Layout

How the Plant Spacing Calculator Works

The calculator works out how many plants fit into your bed based on the spacing between each plant and the layout pattern. In a grid (square) layout, plants sit in straight rows and columns — the number of plants equals (rows + 1) × (columns + 1), where rows and columns are determined by dividing the bed dimensions by the spacing. In a staggered (triangular) layout, alternate rows are offset by half the spacing, and the row-to-row distance shrinks to spacing × √3 ÷ 2 (roughly 86.6% of the plant spacing).

Staggered planting fits about 15% more plants per square metre than grid planting at the same spacing because it uses the space between rows more efficiently. This makes staggered layouts the better choice for ground cover, where fast canopy closure is the goal. For linear boundary plantings rather than area beds, the hedge spacing tool handles single- and double-row calculations.

The extra plants percentage covers losses from transplant failure, poor soil spots, and replacements in the first growing season. A 10% buffer is standard for most planting projects.

What the Numbers Mean

Three outputs appear after calculation: planting area (bed footprint), total plants needed (including extras), and density in plants per square metre. The density figure helps when comparing with nursery recommendations, which are often quoted as “plant 9 per m²” or “plant 5 per m².” The spacing-to-quantity logic mirrors how fabric repeat calculations work for interior projects.

If the density the calculator returns is higher than the nursery recommendation for your species, increase the spacing. If it is lower, you may want to tighten the spacing for faster coverage. The total plants figure is the number to order from the nursery — it already includes the extra percentage for losses.

Getting It Right: Planting Advice

Ground cover plants at 200–300mm spacing give the fastest coverage — typically 1–2 growing seasons to form a solid mat. Popular UK ground covers include Geranium macrorrhizum (300mm spacing), Vinca minor (250mm), and Ajuga reptans (200mm). Mark your planting positions before digging any holes — use a measured stick cut to the spacing length and walk along each row. For staggered layouts, offset every second row by half the spacing distance.

Water each plant in well after planting and mulch the gaps between plants with bark or compost to suppress weeds during the establishment period. Weed control is critical in the first year before the canopy closes — unchecked weeds compete for light and moisture and can overwhelm young plants.

For larger borders, buy plug plants or bare-root stock rather than pot-grown plants. Plugs cost a fraction of pot-grown perennials and establish quickly when planted in autumn or early spring. A 15 m² bed at 300mm staggered spacing needs 225 plants — at £0.50–£1.50 per plug, that is £112–£337 compared to £3–£6 per pot for the same species.

When to Adjust These Numbers

Wider spacing (450–600mm) suits shrubs and taller perennials that spread to fill the gaps within 2–3 seasons. Closer spacing (150–200mm) creates instant impact but costs more in plant numbers. Staggered layouts work best for mass planting and ground cover because the offset rows eliminate bare diagonal lines visible in grid layouts.

For a formal parterre or geometric bed, grid spacing gives clean visual lines. Clay soils may need slightly wider spacing than sandy soils because roots spread more slowly in heavy ground. If planting into raised beds, follow a dedicated soil mix approach for better root development. If you are planting on a slope, tighten spacing by 10–15% to account for soil erosion washing away mulch between plants before the canopy closes.