Understanding your result
The big number is how many plants to buy, with spares included. “Before spares” in the row of small boxes is the number the area actually holds at your spacing.
Density is the number of plants per square foot or per square meter. It is useful for comparing options. If a nursery sells the same groundcover in two pot sizes with two recommended spacings, the density tells you how many of each you would need and which works out cheaper.
For a triangular pattern, the table also gives the distance between rows. This is the measurement you need when setting out. The plants within a row are at the full spacing, but the rows themselves are closer, at about 87% of the spacing, and each row is shifted sideways by half a space.
For a single row, the count includes a plant at each end. That is why a row always needs one more plant than the number of gaps.
How we calculate this
The spacing must be in the same unit as the area. The calculator converts inches to feet (or centimeters to meters) before it divides.
The 0.866 in the triangular formula is the height of an equilateral triangle whose sides are 1. Rows that are 0.866 of a space apart, with every second row shifted by half a space, put each plant exactly one spacing away from its six nearest neighbors. Because the rows are closer together, more rows fit, and 1 ÷ 0.866 = 1.155, which is where the “15% more plants” comes from.
These formulas treat the bed as if the pattern carried on evenly across the whole area. Real beds have edges, and plants cannot sit exactly on the boundary. For large areas the edge effect is small. For a narrow strip only two or three plants wide, set the plants out on the soil in their pots before you dig, and adjust.
The assumptions behind the numbers
| Assumption | Value used | Why |
|---|---|---|
| Spacing | Center to center | This is how plant tags and seed packets state it |
| Triangular row distance | 0.866 × spacing | Geometry of an equilateral triangle |
| Edge of the bed | Ignored | The formulas assume the pattern fills the area. Check narrow beds by laying out |
| Single row | One plant at each end | A row of 10 gaps has 11 plants |
| Spares | 5% unless you change it | Covers transplant losses and layout gaps |
| Rounding | Always up | You cannot buy part of a plant |
Assumptions last reviewed October 3, 2026.
The calculator does not know your plant. The right spacing depends on the mature width, on how quickly you want the ground covered, and on your climate. Use the spacing on the tag or in the seed catalogue as your starting point.
Two worked examples
Groundcover under a tree
A bed measuring 15 feet by 6 feet is being planted with a spreading groundcover sold in trays of 18. The tag says to space plants 8 inches apart, and they will go in on a triangular pattern so the ground closes over evenly.
- Area: 15 × 6 = 90 sq ft
- Spacing in feet: 8 ÷ 12 = 0.667
- Plants: 90 ÷ (0.667 × 0.667 × 0.866) = 233.8, so 234
- With 5% spares: 246 plants
- Trays of 18: 246 ÷ 18 = 13.7, so 14 trays
- Distance between rows: 8 × 0.866 = 6.9 in
On a square grid the same bed would take 203 plants before spares. The triangular pattern uses 31 more, which is the price of faster, more even cover.
A hedge, in metric
A boundary hedge 12 meters long is being planted with bare-root whips at 45 cm spacing.
- Gaps: 12 ÷ 0.45 = 26.7, rounded down to 26
- Plants: 26 + 1 = 27
- With 5% spares: 29 plants
The two spares are worth having with bare-root stock. Heel them into a spare corner, and if a plant in the row fails over the first summer, you have a replacement of the same age and size ready to go in.
Common mistakes
- Measuring edge to edge. Spacing is from center to center. Measuring between the edges of the pots puts the plants too far apart.
- Forgetting the end plant in a row. Length divided by spacing gives the number of gaps. The number of plants is one more.
- Using square-grid numbers for a staggered layout. If you stagger the rows but keep them a full spacing apart, the plants are further from their diagonal neighbors than you intended. Bring the rows in to 87% of the spacing.
- Planting at the pot size instead of the mature size. A shrub in a small pot will not stay small. Space for the width it will reach.
- Buying the exact number. One dead plant leaves a hole that is hard to fill later with a plant of the same size. Buy the spares.
- Ignoring paths and stepping stones. If part of the bed will not be planted, take that area off before you calculate.
Printable shopping list
Print shopping list produces a single page with the number of plants or trays, the spacing, and the row distance for triangular layouts. Take it with you when you set out. A cane cut to the length of your spacing, and a second one cut to the row distance, makes laying out far quicker than measuring every plant with a tape.
Questions people ask
- How many plants do I need per square foot?
- Divide 144 by the spacing in inches multiplied by itself. At 12 inch spacing that is 1 plant per square foot. At 6 inches it is 4, at 8 inches 2.25, at 18 inches 0.44 and at 24 inches 0.25. For a triangular pattern, multiply the result by 1.15.
- What is the difference between square and triangular spacing?
- On a square grid every plant sits at the corner of a square. On a triangular grid each row is shifted by half a space, and the rows sit closer together, so every plant is the same distance from all six of its neighbors. The triangular layout fits about 15% more plants and closes over faster.
- Is spacing measured from the edge of one plant to the next?
- No. Spacing on plant tags is measured from the center of one plant to the center of the next. A tag that says "space 18 inches apart" means the stems go in 18 inches from each other.
- How many plants do I need for a hedge?
- Divide the length of the hedge by the spacing and add one, because there is a plant at each end. A 30 foot hedge with plants 3 feet apart needs 11 plants, not 10.
- Should I plant closer than the tag says for a fuller look?
- You can, and landscapers often do for groundcovers, but there is a cost. Closer spacing means more plants to buy, more competition for water, and sometimes more disease because air moves less freely. For shrubs and perennials, the tag spacing is based on the mature width and is usually worth following.
- Why add spares?
- A few plants in every tray fail to establish, and laying out on the ground often shows a gap the sum did not predict. Five percent extra covers both. For cheap plugs and groundcovers, ten percent is sensible.
Built and reviewed by Bertha
Last updated · How we work out our numbers