How-to Guide
Building Raised Beds on a Concrete or Paved Surface
The short answer
Raised beds work fine on a concrete patio or paved surface, with two adjustments. First, depth: because roots cannot grow down into native soil, the bed must hold all the soil the plants need, so aim for greater depth than a bed on open ground, generally at least 18 inches, and 18 to 24 inches for deep-rooted crops like tomatoes and root vegetables.
Second, drainage. Water has to be able to leave the bed since it cannot soak into the ground below. A common recommendation, echoed by the RHS for beds over hard surfaces, is a layer of at least three inches of coarse gravel or stone topped with a permeable landscape membrane before adding soil, so the bed drains freely without the gravel mixing into the mix. Keep the base off the concrete slightly or slope the site so water isn't trapped, and remember that a paved surface radiates heat that can warm the bed's base and dry it faster.
Depth: the roots only get what you give them
On open soil, a shallow raised bed still lets roots forage into the ground beneath. On concrete there is no beneath, so the bed's depth is the entire root zone. For general vegetables aim for at least 18 inches of soil, and for deeper-rooted crops such as tomatoes, carrots, or potatoes, plan on 18 to 24 inches. Shallower beds dry out fast and limit which crops you can grow; leafy greens and herbs tolerate less depth than fruiting or root crops.
Drainage over a hard surface
The Royal Horticultural Society recommends that beds built over concrete or pavement have a drainage layer of at least three inches of coarse gravel or stones, covered with a geotextile (landscape) membrane, before the growing medium goes in. The gravel gives water somewhere to collect and move, and the membrane stops soil from washing down and clogging it. Make sure water can actually exit the bed at the base or edges, and note that a bed built on a slanted slab will drain unevenly, so level the site or build in a slight, deliberate slope toward an outlet.
Root heat and moisture
- Concrete absorbs and re-radiates heat, so the bottom of the bed can run hot and dry in summer; deeper soil buffers this.
- Expect to water more often than an in-ground bed, since there's no subsoil moisture reservoir to draw on.
- A light-colored bed or a gap between bed and slab reduces heat buildup at the base.
- For the frame itself and mix, see our building a raised bed guide.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Royal Horticultural Society - Raised Beds — For raised beds on solid surfaces such as concrete or paving, lay a drainage layer of coarse gravel or stones at least a few inches deep, covered with a permeable membrane, so the bed drains freely; provide adequate soil depth for the crops grown.
- Texas A&M AgriLife Extension - Raised Bed Gardening (E-560) — Raised beds must provide adequate soil depth for root development and good drainage; deeper beds are needed where roots cannot penetrate the underlying surface.