Plant spacing: how many plants do I need?

By Francesco Zinghinì

The spacing formula

Each plant “owns” a square of ground equal to its spacing squared, so:

square grid: plants = area (sq ft) ÷ spacing² (ft)
triangular grid: plants = area ÷ (spacing² × 0.866)

“On center” means from the center of one plant to the center of the next. The plant-spacing tool handles both patterns; the plant-spacing table lists plants per 100 sq ft by spacing.

Worked example: 100 sq ft at 12 inches on center

• Square grid: 100 ÷ 1² = 100 plants.
• Triangular grid: 100 ÷ (1² × 0.866) = 100 ÷ 0.866 = 115 plants.

Same bed, same spacing — but the staggered layout fits 15 more plants, because triangular packing is more efficient than a square grid. For groundcovers where you want quick, even coverage, that is a real material difference.

Square vs. triangular layout

A square grid lines plants up in rows and columns — simple to lay out and fine for formal plantings. A triangular (staggered) grid offsets each row by half a space, so every plant sits in the gap of the row before it; it covers ground faster and looks more natural, at the cost of about 15% more plants. For mass groundcover, triangular is the usual choice; for a tidy geometric bed, square.

Choosing the spacing

The right spacing is the plant’s mature spread, not its size in the pot. Space plants so they just touch at maturity: too close and they crowd and compete; too far and you get gaps and weeds for a season or two. Tighter spacing gives faster coverage (useful for groundcovers and erosion control) but costs more plants; wider spacing is cheaper and lets each plant reach full size. Typical ranges run from a few inches for small groundcovers to several feet for shrubs — check the plant tag for the mature spread and space to that.

Measuring the bed

Break an irregular bed into rectangles and simple curves, measure each, and add the areas — the same method the lawn-area estimator uses. For a bed you will mulch after planting, the mulch-ring tool (for rings around trees) and the mulch calculator size the mulch; read the mulch guide for depth.

Quick reference: plants per 100 sq ft by spacing (square grid)

plants = 100 ÷ spacing²:

• 6 in (0.5 ft) → about 400 plants (about 462 triangular).
• 12 in (1 ft) → 100 plants (about 115 triangular).
• 18 in (1.5 ft) → about 44 plants (about 51 triangular).
• 24 in (2 ft) → 25 plants (about 29 triangular).
• 36 in (3 ft) → about 11 plants (about 13 triangular).

Halving the spacing roughly quadruples the plant count, because area scales with the square of distance — the single biggest lever on how many plants (and how much money) a bed takes.

Groundcover, perennials and shrubs

Spacing depends on what fills the bed. Groundcovers are usually set close (6–12 in) and often on a triangular grid for fast, even coverage and erosion control. Perennials sit at their mature clump width, commonly 12–24 in. Shrubs space by mature spread, often 2–5 ft or more. The plant tag’s “spacing” or “mature spread” is the number to use; when a tag gives a range, tighter fills in faster and wider is cheaper and lets each plant show its natural form. Remember the count is per unit area, so an odd-shaped bed is best broken into rectangles and simple curves, each counted on its own and then added together.

Turning the count into a shopping list

Multiply the per-bed count by the number of beds, then add a few spares per variety for losses and for replacing any that fail to establish — nurseries sell out of a given plant, so buying the spares up front saves a return trip. If plants come in flats or trays of a fixed number, round up to whole trays. Then size the mulch that goes over the finished bed with the mulch calculator (see the mulch guide), and the water it needs with the watering-needs tool.

This math tells you the plant count for a given spacing; it does not choose the plant, judge whether it suits your climate, soil or light, or diagnose plant health — those are questions for a plant tag, a nursery, or your local extension office. Buy a few extra to replace any that do not take, and treat the count as a starting point you can adjust to your design.

Key takeaways

• Square grid: plants = area ÷ spacing². Triangular: divide by an extra 0.866 (about 15% more).
• Spacing is measured on center — from the center of one plant to the next.
• 100 sq ft at 12 in on center is 100 plants (square) or about 115 (triangular).
• Halving the spacing roughly quadruples the count — the biggest lever on plants and cost.
• Space to the plant’s mature spread from the tag; buy a few spares per variety.