What this calculator works out
This calculator divides a bed area by the square of the plant spacing to give a shrub count, then adds an allowance for edges and awkward corners.
The spacing figure should be the mature spread of the shrub, not the size of the pot it arrives in. That is the single decision that determines whether a border works in five years.
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Before you order plants
- Use the eventual spread from the plant label or a reference, not the current size. A shrub sold at 40 cm across may reach 2 m.
- Spacing is usually set at roughly the mature spread for full cover, or slightly less for a dense effect sooner.
- The extra allowance covers edges and irregular bed shapes rather than plant losses.
- Mixed borders need planning plant by plant rather than by a single spacing figure.
Setting plants on a square grid at spacing s gives one plant per s². Offsetting alternate rows — triangular or staggered spacing — gives one per about 0.866 s², roughly 15% more plants in the same area at the same minimum distance apart. It also looks less regimented, which is why it is standard for naturalistic planting.
How this calculator works
Area divided by the square of the spacing:
Shrubs = bed area ÷ spacing² × (1 + allowance ÷ 100), rounded upSquaring the spacing assumes a square grid. For triangular spacing, divide the result by 0.866 to get the higher count, or accept the square figure as a conservative estimate.
Worked example: a 12 m² border
Using the default figures — 12 m² with 1 m spacing and a 10% allowance:
- Base count: 12 ÷ 1 = 12
- With allowance: 14 shrubs
Fourteen shrubs at 1 m spacing fills a 12 m² border. But if those shrubs mature at 1.5 m across, the correct spacing is 1.5 m and the border holds only seven — half as many, at roughly half the cost. Ordering fourteen would produce a border that looks right for two years and needs thinning by year four. The spacing figure is worth checking twice.
Common mistakes
- Spacing by pot size rather than mature spread. The most expensive planting mistake.
- Planting densely for immediate effect. It costs more and needs undoing later.
- Using one spacing for a mixed border. Different shrubs need different room.
- Forgetting the edge. Plants at the front need space to spread forwards.
- Ignoring height as well as spread. A tall shrub at the front shades everything behind it.
Frequently asked questions
Should I plant closer for quicker cover?
It is a real trade-off. Close planting gives a filled border sooner and costs more, and requires thinning or hard pruning within a few years. A common compromise is to plant at the correct spacing and fill the gaps with annuals or short-lived perennials for the first two or three seasons.
How do I space a mixed border?
Plan it plant by plant on paper first, working from the largest to the smallest. Position structural shrubs at their mature spread, then fill between them. A single spacing figure works for a block of one species and not for a mixed planting.
What about ground cover?
Ground cover is usually specified as plants per square metre rather than by spacing, commonly 5 to 9 for vigorous species and more for slower ones. The aim is to close the canopy within two seasons, so the spacing is deliberately tighter than mature spread.
When is the best time to plant shrubs?
Autumn is generally best in the UK — the soil is still warm, rainfall is reliable, and roots establish before the following summer. Bare-root plants are only available from late autumn to early spring and are considerably cheaper than container-grown. Container-grown shrubs can be planted year-round but need watering through their first summer.
Is what I enter stored?
No. Measurements are processed in your browser and never transmitted or retained.
Related tools
References
- Royal Horticultural Society — shrub selection, spacing and planting guidance
- GOV.UK — guidance on planting, tree health and biosecurity
Sources are checked at publication and can change — how I choose and check references.