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SOIL & MATERIALS

Raised Bed Soil Depth Guide

Bed height and usable rooting depth are not always the same. Roots may continue into suitable soil below an open-bottom bed, while a bed on paving must provide its full growing depth inside the frame. [1][2]

Begin with what lies below

For an open-bottom bed over native soil, Oregon State describes loosening and mixing the soil below the frame as an option for deeper root growth. [2]

University of Maryland separates beds over usable soil from beds on non-permeable surfaces because roots and drainage face different limits. [1]

Hard-surface guidance has a specific context

For beds on a driveway or other non-permeable surface, Maryland guidance gives a minimum 8-inch depth for leafy greens, beans, and cucumbers and 12–24 inches for pepper, tomato, and squash. Those numbers are for that hard-surface scenario, not a universal raised-bed rule. [1]

Depth changes construction and water planning

OSU advises reinforcing frames longer than 6 feet or taller than about 18 inches because the walls must hold the weight of soil, plants, and irrigation water. [2]

Raised beds can dry faster than in-ground gardens, so deeper or isolated beds still need a watering plan suited to their soil and climate. [3]

Use this guide with Grownestia

Calculate soil from your chosen depth

Use the actual remaining fill depth rather than a universal preset.

LettuceCucumberPepperTomatoZucchini

Sources

  1. University of Maryland Extension: Soil to Fill Raised BedsReviewed by Grownestia 2026-09-09
  2. Oregon State University Extension Service: Raised bed gardeningReviewed by Grownestia 2026-09-09
  3. University of Minnesota Extension: Raised bed gardensReviewed by Grownestia 2026-09-09