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Plant Spacing Calculator Guide
How many plants fill a bed — and why the offset grid everyone uses actually fits more.
Square grid: plants = area ÷ spacing²
Triangular grid: plants = area ÷ (spacing² × 0.866)
That 0.866 is sin(60°) — the height of an equilateral triangle. It's why triangular spacing fits 15.5% more plants in the same bed at the same spacing.
Triangular Beats Square, for Free
Offset each row by half a spacing and shift it up so the plants form equilateral triangles instead of squares. Every plant is still the same distance from its neighbours — you haven't crowded anything.
But the rows nest closer together, by a factor of sin(60°) = 0.866, so you fit 15.5% more in the same area. It's the same packing efficiency that makes a honeycomb hexagonal. It also looks natural rather than gridded, which is usually what you wanted anyway.
Space for the Plant It Becomes
This is the mistake that costs money twice. The plant in the pot is 6 inches across; the tag says it matures at 3 feet.
Space at 6 inches and it looks wonderful for one season, then becomes an overcrowded mess that you thin out by throwing away plants you paid for. Space at 3 feet and it looks sparse and embarrassing for two years, then looks correct forever. The second one is right.
Filling the Gap Honestly
If the bare look in year one bothers you, mulch it properly and use annuals in the gaps — they're cheap, they're meant to be temporary, and they come out when the perennials need the room.
What you shouldn't do is plant the permanent stuff too close and promise yourself you'll thin it later. Nobody thins later. The plants get big, the roots knit together, and thinning means killing something established.
Crowding Is a Disease Problem
Plants packed too tight don't just compete for light and water — they stop air moving between them.
Leaves that stay damp after rain or morning dew are how powdery mildew, black spot and most fungal problems get started. Correct spacing is a disease control measure, which is why the tag's number is a horticultural recommendation and not a suggestion from the marketing department.
Hedges Are the Exception
If you want a continuous solid hedge, deliberate close planting is the point — you're asking the plants to merge into a single mass.
Even then, use the recommended hedge spacing for that species rather than eyeballing it. Too tight and the bottom goes bare as the plants shade each other out, which is exactly the failure mode you were trying to avoid.
Related: raised bed soil calculator, mulch calculator, topsoil calculator.
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