Plant spacing calculator: how many plants you need

How the calculator counts plants

Spacing on a plant tag is "on center": the distance from the middle of one plant to the middle of the next. So a bed 12 feet long with plants 18 inches on center holds 8 per row (144 inches divided by 18), and a bed 4 feet wide holds 2 rows (48 divided by 18, rounded down). That is 16 plants in a square grid. The calculator leaves half a spacing between the outer plants and the bed edge, which is where mature plants stop short of the lawn or path instead of flopping over it.

A triangular, or staggered, layout offsets every second row by half a spacing and pulls the rows closer together, to 0.866 times the spacing. The same 12 by 4 foot bed at 18 inches then fits 3 rows instead of 2, and 22 plants instead of 16. Staggering fits roughly 15 percent more plants in the same area and, more usefully, hides the row lines. Nearly every professional planting plan uses it for ground covers and mass perennials. Square grids are for vegetables, formal hedges and anything you need to walk between.

The diagram at the bottom redraws as you type. Print it or screenshot it, then set the plants out on the bed in their pots before you dig a single hole. Adjusting a pot is free. Adjusting a planted hosta is a shovel job.

Common plant spacings

The "I know the plant" mode uses the mature spread from the nursery tag, which is what the ranges below are. Pick the low end when you want a hedge or a solid mass in two seasons, the high end when you are planting specimens or paying full price for large pots. The ranges are for the common landscape varieties; a dwarf or a giant cultivar shifts them, so read the tag.

Why tight spacing is not the shortcut it looks like

Planting closer than the tag says gives you a full bed in year one and a maintenance problem in year three. Shrubs shade each other out and go bare at the bottom. Perennials get crown rot where the foliage never dries. Lavender and other Mediterranean plants are the classic victims: they look fine crowded for a summer and then die in wet patches over winter. The plant spread on the tag is the spread at maturity, and the gap in between is where the light and the airflow come from.

The one exception worth making is annuals and ground covers, where you are buying the plants for this season and can pack them in at the low end of the range or a bit under. For everything else, plant at the mature spacing and fill the gaps for the first two years with mulch, annuals or a cheap fast perennial you are willing to pull.

On the other side, spacing too wide is just money spent on mulch and weeding. A border that never closes needs weeding forever. If the budget only covers half the plants, plant half the bed properly rather than the whole bed thinly. Mass plantings of one variety at correct spacing look better than a thin scattering of twelve kinds, and they are easier to maintain.

Buying the right number

Take the calculator's total and add 5 to 10 percent for a curved bed or for the plants that arrive damaged. Nurseries sell perennials in flats of 18 or 32 plugs and shrubs individually, so round up to the flat. If you are ordering plugs or bare-root plants online for a large area, the per-100-sq-ft numbers in the first table make quick work of it: a 300 square foot slope in a staggered 12-inch ground cover is 345 plugs, about 11 flats of 32.

For hedges, measure the run in feet, multiply by 12, divide by the spacing, and add one plant so that both ends are covered. A 40-foot arborvitae screen at 4 feet on center is 11 plants, not 10. The calculator gives you the same thing if you enter the run as the length and a width equal to a single spacing.

Frequently asked questions