Garden bed cost

A new planting bed costs $10 to $30 a square foot installed, typically around $18. That covers taking out the lawn, preparing the soil, edging, plants and mulch. A 10 by 12 foot bed along a patio, 120 square feet, is therefore $1,200 to $3,600, and about $2,200 at the typical rate.

Plants are rarely the biggest line. Soil preparation and plant size decide the price, and the soil preparation is also what decides whether the bed is still alive in three years.

What it costs

What drives the price per square foot

Plant density and size. At the low end a bed is planted sparsely with one-gallon perennials and left to fill in. At the top it is planted with three and five-gallon shrubs close enough to look finished on day one. The same 120 square feet can hold $400 or $2,500 of plants.

What comes out first. Cutting a bed from an ordinary lawn is quick. Removing overgrown shrubs, roots and old landscape fabric is slow, and it is labor and disposal.

Soil. Good loam needs a little compost. Compacted builder's clay needs breaking up to 8 inches and several inches of organic matter, and on a badly drained site it may need raising.

Edging. Steel and stone cost more per foot than a cut spade edge or plastic, and they last.

Access. A bed behind the house with no gate wide enough for a wheelbarrow is priced by the trip.

Soil, edging and spacing

Soil preparation for an ornamental bed means removing the turf entirely, loosening the soil to 8 to 12 inches, and working in 2 to 3 inches of compost. Do not simply pile topsoil over grass: the grass grows through it within a season.

Edging types, roughly from cheapest:

• Cut spade edge, a vertical trench recut once or twice a year, close to free and the look many designers prefer
• Plastic or composite strip, $4 to $8 a linear foot installed, which heaves in frost if it is not staked deeply
• Steel or aluminum, $8 to $15, crisp and nearly invisible, and it lasts decades
• Brick, paver or stone, $10 to $15 and above, which doubles as a mowing strip if set flush with the lawn

Plant spacing follows mature width, not pot size. Most perennials sit 12 to 18 inches apart, which is about one plant per 1 to 2 square feet. Small shrubs go 3 feet apart and larger ones 4 to 6. A bed planted at pot spacing looks full in May and is a tangle to be thinned by the second summer.

Mulch goes on at 2 to 3 inches after planting. Mulch delivery covers how many yards that takes.

Raised vegetable beds

Vegetable beds are priced per bed rather than per square foot, because the box is most of the cost.

A 4 by 8 foot bed 12 inches deep holds 32 cubic feet of soil, a little over a cubic yard. At $40 to $80 a yard for a proper raised-bed mix, the soil is cheap, and it is the part people economize on by filling with garden soil, which compacts in a box and drains badly.

Cedar lasts 10 to 15 years. Galvanized steel lasts longer and heats faster in spring. Pressure-treated timber is used, and many growers line it or avoid it for edible crops. Stone or block is permanent and costs the most.

Keep beds no wider than 4 feet so the middle can be reached from both sides, and leave paths at least 2 feet wide, 3 if a wheelbarrow has to pass.

What makes a new bed fail

Grass coming back. Bermuda, zoysia and quackgrass regrow from runners left in the soil. Strip the roots or smother the area for a season before planting.

Wet feet. A bed in a low spot, or where a downspout discharges, drowns most shrubs. Fix the water first. French drains and simple regrading are cheaper than replanting twice.

No watering plan. New plants need water two or three times a week for their first summer. A bed beyond the hose's reach needs drip, and adding it after planting means digging through roots. See irrigation for what a drip zone costs.

Landscape fabric under the mulch. It stops perennials spreading, and within a few years weeds root into the decomposed mulch on top of it.

Wrong plant, wrong light. A sun perennial in a shade bed limps along for two years and dies. Watch where the sun falls in midsummer before choosing plants.

Frequently asked questions

How many plants does a 100 square foot garden bed need?

With perennials at 12 to 18 inches, around 50 to 90. A more realistic mixed bed, with three or four shrubs as structure and perennials between them, is 30 to 50 plants. Fewer, larger drifts of the same plant look better than one of everything.

Should I build raised beds or plant vegetables straight into the ground?

In-ground beds cost almost nothing beyond compost and suit good, well-drained soil. Raised beds suit clay, poor drainage, contaminated urban soil, bad backs and gardeners who want tidy paths. At $250 to $900 a bed, they pay back only if they make you garden more.

Is it cheaper to smother the lawn than to dig it out?

Yes. Sheet mulching with cardboard and 4 inches of compost or mulch costs little more than the materials and kills most lawns in two to four months. It is too slow for a bed you want this spring, and it does not stop spreading grasses with deep runners.

How deep should soil be in a new flower bed?

Loosened and amended soil to 8 to 12 inches for perennials and shrubs, and 12 inches or more in raised vegetable beds. Trees need wide, not deep, preparation: roots spread sideways.

Why do contractors quote garden beds so differently?

Mostly plant size and density, then how much soil preparation is included. Ask each quote for the plant list with pot sizes and a line saying how deep the soil is worked. Once those match, the quotes usually do too.