How many plants do I need for a garden bed?

To find how many plants a bed needs, divide the bed's area by the area each plant takes up. For a square grid that is:

Plants = bed area (sq ft) ÷ (spacing in ft × spacing in ft)

Spacing is the plant's mature width. A 12 × 6 ft bed is 72 sq ft; at 2 ft spacing that is 72 ÷ 4 = 18 plants. Most beds mix plants of different sizes, so you do this sum once for each group and add the results. The rest of this page shows how, with a worked example and a quick-reference table.

Step 1: measure the bed

Measure the length and width in feet with a tape. For an L-shaped or irregular bed, split it into rectangles, work out each area (length × width) and add them. For a curved bed, measure the width at several points and use the average. If you have no tape, one adult stride is roughly 3 feet, which is close enough for a first estimate.

Step 2: find each plant's spacing

Look for "mature width" or "spread" on the plant tag. That number is your spacing: plants set that far apart, center to center, will just touch when fully grown. If a tag gives a range such as "18–24 in", use the middle (about 1.75 ft) or the upper end if you are patient and on a budget.

Two cautions:

• Tags often describe growth in ideal conditions. In poor soil or a short season plants may stay smaller; in long, warm seasons some get bigger.
• Shrubs keep growing for years. Space them for the size they reach in 5–10 years, not the size of the pot.

Step 3: square or triangular spacing

There are two common layouts.

• Square spacing puts plants in a grid of rows and columns. Each plant "owns" a square of spacing × spacing. Easy to lay out with a string line.
• Triangular spacing offsets each row by half a spacing, so every plant sits at the corner of an equilateral triangle. Each plant then owns spacing × spacing × 0.866. You fit about 15% more plants, the gaps close evenly, and the result looks less like a parade ground.

Triangular plants per area = square plants per area ÷ 0.866 (or × 1.155).

Plants per 100 square feet

The exact figures are 100, 44.4, 25, 11.1 and 6.25 for the square grid, and 115.5, 51.3, 28.9, 12.8 and 7.2 for the triangular grid. Scale them to your bed: a 50 sq ft bed at 1.5 ft triangular spacing needs about 51 × 0.5 ≈ 26 plants.

Worked example: a 12 × 6 ft bed

Say you want a classic three-layer border along a fence: shrubs at the back, perennials in the middle, a low edging plant at the front. The bed is 12 ft long and 6 ft deep, so 72 sq ft.

Divide the depth among the layers to match each group's spacing:

You can check the back row another way: 12 ft of length at 3 ft spacing is 12 ÷ 3 = 4 plants, centered 1.5 ft in from each end and 3 ft apart (at 1.5, 4.5, 7.5 and 10.5 ft). The first and last plant sit half a spacing from the bed's edge, which is where they belong.

Each layer here is a single row, so triangular spacing does not change the count. It pays off where one plant fills several rows, such as a broad drift of perennials or a groundcover: there, stagger the rows and use the triangular column of the table.

How full will it look?

A grown plant is roughly a circle, not a square, so even perfect spacing leaves small gaps. The share of ground covered is about 79% on a square grid and about 91% on a triangular grid. For the example above:

• Shrubs: 4 × 3.1416 × 1.5² = 28.3 sq ft
• Perennials: 6 × 3.1416 × 1² = 18.8 sq ft
• Edging: 12 × 3.1416 × 0.5² = 9.4 sq ft
• Total 56.5 sq ft of 72, which is 78.5%

That level of cover is what you want: full enough to shade out most weeds, with a little air between plants so foliage dries and diseases spread less. Mulch covers the bare soil while the plants grow in. If you want to know how much mulch that takes, see how much mulch do I need.

Groups, odd numbers and repetition

Numbers on paper rarely match how a bed looks best. Some common adjustments:

• Plant in groups. Three or five of one perennial read as a deliberate drift; one of each of eleven things reads as a plant sale. Many designers prefer odd numbers because they are harder for the eye to split into pairs.
• Repeat. Using the same plant in two or three spots along a long bed ties it together.
• Round sensibly. If the sum says 4.4 plants, buy 4 and let them fill in. Rounding up every group is how beds end up crowded.

Common mistakes

• Spacing from the pot, not the mature width. A 1-gallon shrub that grows 5 ft wide needs 5 ft, even though it looks lost for the first year or two.
• Forgetting the edges. Plants against a fence, wall or path need half their spacing between their center and the edge, or they will lean or spill over.
• Counting only one layer. Do the sum for each group of plants separately, then add.
• Ignoring the timeline. Perennials usually fill in over two or three seasons ("sleep, creep, leap"). Shrubs can take several years.

Quick checks before you buy

1. Does the total plant count roughly match the area table above for the spacings you chose?
2. Is every shrub's mature width less than the depth of the bed? A 6 ft wide shrub in a 4 ft deep bed will spill onto the lawn or path.
3. Have you left room to walk in and weed? In beds deeper than about 5 ft, a few stepping stones help.

If you would rather not do the arithmetic, the free plant calculator does it for you from length, width and spacing. And if you want the plants chosen as well as counted, FloraVista can build a list with quantities for your exact bed from one photo: start here.