How Far Apart to Plant Perennials: Spacing Guide and Chart

Spacing is where most new perennial beds go wrong. Small nursery pots make it tempting to plant close together for an instant full look, but perennials keep growing for years. Plants set too close compete for water and light, trap humid air that spreads disease and need dividing far sooner. Plants set too far apart leave bare soil for weeds. This guide explains how to measure spacing, gives a spacing chart for popular perennials, shows how to work out how many plants you need, and covers the layout tricks that make a bed look full sooner.

Space for Mature Size, Not Pot Size

The single most important rule is to space perennials for the size they will reach, not the size they arrive. University of Georgia Extension recommends spacing plants according to their mature size, or the size they will reach by their third year of growth. That is the point when most perennials fill their allotted space.

The plant tag or a plant profile lists spread, the mature width of the plant. For most perennials, a spacing equal to that spread means neighbors will just touch when they are full grown, with no gaps and no crowding. For a softer, more blended look, you can space plants slightly closer than their full spread, by about a quarter, and let them knit together.

Spacing is always measured from the center of one plant to the center of the next, sometimes called on-center spacing. Two plants with a spread of 2 feet, planted 2 feet apart, each have a 1-foot radius of space that meets in the middle.

Spacing Rules of Thumb by Plant Size

When you do not have a specific spread for a plant, height is a reliable guide, since taller perennials usually spread wider. Colorado State University Extension gives these general distances: dwarf perennials 6 to 12 inches apart, intermediate perennials 12 to 18 inches apart and tall perennials 18 to 36 inches apart.

Within each range, use the closer spacing for upright, clump-forming plants that stay narrow, and the wider spacing for plants that sprawl, spread by underground stems or form broad mounds. Catmint and bee balm, for example, both spread wider than their height suggests, while many ornamental salvias stay compact.

Spacing Chart for Popular Perennials

The chart below gives recommended spacing for perennials profiled on this site, based on their typical mature spread. Where a plant comes in sizes, use the closer spacing for dwarf or compact varieties and the wider spacing for full-size types.

How Far Apart to Plant Popular Perennials

Perennial	Typical Spread	Spacing
Astilbe	1 to 3 feet	12 inches (dwarf) to 18 to 24 inches
Bee balm	2 to 3 feet, spreading	18 to 24 inches
Black-eyed Susan	1.5 to 2.5 feet	18 to 24 inches
Catmint	2 to 4 feet	18 inches (compact) to 2 to 3 feet
Coneflower	1.5 to 2 feet	18 to 24 inches
Coral bells	12 to 24 inches	12 to 18 inches, up to 24 for large types
Creeping phlox	1 to 2 feet	12 to 18 inches
Daylily	1.5 to 3 feet	18 to 24 inches, up to 3 feet for large types
Garden phlox	2 to 3 feet	18 to 24 inches
Hosta	1 to 6 feet	1 foot (miniature) to 4 to 5 feet (giant)
Lavender	1.5 to 3 feet	18 to 24 inches, 2 to 3 feet for lavandins
Peony	2 to 4 feet	3 to 4 feet
Russian sage	2 to 4 feet	2 to 3 feet, 18 to 24 inches for dwarf types
Salvia	1.5 to 2 feet	18 to 24 inches
Sedum	1 to 2 feet	12 inches (creeping) to 18 inches (upright)

Plants that need good airflow to avoid mildew, such as garden phlox, bee balm and lavender, should never be crowded below the low end of their range. Peonies are long-lived and resent moving, so give them their full 3 to 4 feet from the start.

Why Proper Spacing Matters

Crowded perennials look lush for a season or two, then problems set in. University of Georgia Extension notes that correct spacing keeps vigorous plants from overwhelming weaker neighbors and allows enough air movement to reduce disease. Powdery mildew, leaf spots and crown rot all thrive in the still, humid air inside a tightly packed planting. For garden phlox, one of the most mildew-prone perennials, Iowa State University Extension advises dividing overcrowded plantings to improve air circulation.

Crowding also increases competition below ground. Roots of closely spaced plants fight for the same water and nutrients, so plants weaken, flower less and need watering more often. Over time, the centers of crowded clumps die out, and you end up dividing every year or two instead of every three to five.

The opposite mistake, spacing too wide, is easier to live with but leaves bare ground that weeds will claim. The simplest fix is to fill gaps with annuals or mulch for the first couple of seasons while the perennials grow in.

Be Patient: Sleep, Creep, Leap

Properly spaced perennial beds look sparse at first. That is normal, and it is the sign of a bed that will still look good in five years. Gardeners describe the typical pattern with an old saying, which University of Georgia Extension also uses: “The first year they sleep, the second year they creep, and the third year they leap.”

In the first year, a new perennial puts most of its energy into roots and stays close to its nursery size. In the second year, it grows noticeably and flowers more. By the third year, most perennials reach close to full size and fill their space. Plan for that third-year size, and use temporary fillers until then.

Good fillers include annuals such as zinnias, cosmos, marigolds and sweet alyssum, which flower all season and are easy to remove as the perennials expand. A 2- to 3-inch layer of mulch over the bare soil also reduces weeds and keeps the bed looking finished.

How Many Plants Do You Need?

Once you know the spacing, you can work out how many plants a bed needs. In a simple square grid, each plant occupies a square with sides equal to its spacing. Divide the bed area by that square to get the number of plants.

Plants Needed per 100 Square Feet

Spacing	Area per Plant	Square Grid	Staggered Grid
12 inches	1 square foot	100	115
18 inches	2.25 square feet	44	51
24 inches	4 square feet	25	29
30 inches	6.25 square feet	16	18
36 inches	9 square feet	11	13

For example, a 4-by-10-foot bed has 40 square feet. Planted with coneflowers at 18 inches, it needs about 40 divided by 2.25, or 18 plants in a square grid. A staggered grid, where each row is offset from the one beside it, fits about 15 percent more plants into the same area and covers the ground more evenly.

Lay Out Plants in Groups and Staggered Rows

How you arrange plants matters as much as the distance between them. Colorado State University Extension recommends planting the same variety in groups of three, five or seven and avoiding straight rows. Instead, use a scattered or triangular pattern so one group blends into the next.

A staggered, triangular layout puts each plant at the point of a triangle with its neighbors, all at the same spacing. It looks more natural than a grid, closes gaps faster and leaves fewer straight lines of bare soil for weeds. Within a group, keep the spacing for that plant. Between groups of different plants, use the average of the two spacings. For example, between a group of catmint at 24 inches and a group of coral bells at 12 inches, leave about 18 inches.

Before you dig, set the pots out on the bed in their final positions and step back to look. It is much easier to adjust spacing by moving pots than by moving planted perennials. Place taller plants at the back of a border, or in the center of an island bed, and graduate to shorter plants toward the edges.

Spacing Groundcovers and Mass Plantings

Groundcover perennials, such as creeping phlox and creeping sedum, are often planted a little closer than their full spread, because the goal is a solid mat as quickly as possible. At 12 inches apart, creeping phlox usually knits together in two or three seasons. Closer spacing gives faster coverage at a higher cost, while wider spacing saves money if you can wait.

For slopes or large areas where weeds are a concern, the faster coverage of closer spacing usually pays for itself in reduced weeding. For mixed borders, stick with mature spread.

Adjust Spacing for Your Conditions

Published spreads describe a plant in typical garden conditions, and your garden may push it larger or smaller. In rich, moist soil and long growing seasons, many perennials grow bigger than their tag suggests, so use the wider end of the spacing range. In lean, dry or rocky soil, in the coldest zones and in part shade for sun lovers, plants usually stay smaller, so the closer end works well.

How a plant spreads matters too. Clump-forming perennials such as coral bells, daylilies and hostas widen slowly and predictably from a central crown. Perennials that travel by underground stems, such as bee balm, can wander well beyond their stated spread within a few seasons. Give spreaders extra room, edge them, or plant them where wandering is welcome, and keep them away from slower neighbors they could overwhelm.

Finally, think about how long you want to wait. Spacing at the full mature spread gives the healthiest long-term bed. Spacing about a quarter closer fills in a season sooner, at the cost of dividing a year or two earlier.

Frequently Asked Questions

Short answers to common spacing questions.

What Happens If I Plant Perennials Too Close Together?

They compete for water, nutrients and light, grow weaker and flower less, and are more prone to mildew and rot from poor air circulation. They also need dividing sooner. You can fix crowding by lifting and moving or dividing plants in spring or fall.

Is Spacing Measured From the Edge or the Center of the Plant?

From the center. Spacing on plant tags and in charts is on-center: the distance from the middle of one plant to the middle of the next.

How Far From a Fence or Wall Should I Plant Perennials?

Plant at least half of the plant’s mature spread away from a fence, wall or path, so it can reach full size without being cut back. Add a few more inches against walls, which block air movement and shed rain.

Can I Plant Perennials Closer Together in Containers?

Yes, for a single season, since container plantings are often meant to look full right away. Plan to divide or replant the perennials into the garden after a year, before they become root-bound and overcrowded.