How Deep Should a Raised Garden Bed Be? Soil Depth Guide

How deep should a raised garden bed be? For most vegetables, deep enough to hold at least 10 in of soil. Root crops, potatoes and beds built on a hard surface need more. This guide walks you through the depth each crop needs, how much soil each depth takes, and what to put under the bed.

• How deep should a raised garden bed be for most vegetables?
• Is 12 inches deep enough for a raised bed?
• How deep should a raised bed be for potatoes and root crops?
• Can a raised bed be too deep?
• How much soil does a raised bed need?
• How wide and long should a raised bed be?
• What do you put in the bottom of a raised bed?
• What wood is safe for a raised vegetable bed?
• How do you plan your raised bed?

How deep should a raised garden bed be for most vegetables?

Start with the soil, not the boards. University of Georgia Extension puts it plainly: most garden crops need at least 10 in of soil to thrive. Greens, herbs, flowers and most vegetables do well at that depth.

Our plan engine builds bed walls from stacked 2x6 boards. A 2x6 is really 5.5 in tall, so two boards make an 11 in wall. We fill the soil to 1 in below the top, which leaves 10 in of soil, right at the extension minimum. That is the depth we suggest for most first beds.

What if the bed sits on open ground?

A bed on native soil gets a bonus: roots can grow down past the frame. UGA notes that if your bed is shallower than 10 in, you should till the existing soil below it. Loosen the ground under the frame before you fill it, and the plants treat that loosened layer as part of the bed.

Is 12 inches deep enough for a raised bed?

Yes. A 12 in bed clears the 10 in minimum with room to spare, so it suits greens, herbs, flowers and most other vegetables. It is also a common answer when people ask how deep a raised garden bed should be, because it balances root room against soil cost.

The catch is what sits under the bed. On open, loosened ground, 12 in is plenty for nearly everything. On a patio, a driveway or compacted fill, the roots stop at the frame. In that case the bed's own depth is all the soil your plants get.

How deep should a raised bed be for potatoes and root crops?

Go deeper. UGA warns that on a hard surface, the 10 in minimum may not be deep enough for some crops, like potatoes. Tubers and long roots need more loose soil below them than a bed of greens does.

In our plans, a three-board wall is 16.5 in tall and holds 15.5 in of soil. We suggest that depth for root crops and potatoes, and for any bed that sits on a hard surface. It gives tubers and long roots room to grow without hitting the bottom.

These are the three depths our plan engine offers. The suggestions come from our plans and the extension guidance above.

Can a raised bed be too deep?

Plants rarely mind deep soil, but you will notice it in your wallet and your back. Every extra inch of height means more soil to buy, haul and fill. Taller walls also hold back more weight. UGA reminds you that the bottom must hold the weight of the soil when it is wet and still let water drain.

The numbers grow fast. In our plans, a 4x8 ft bed at 11 in tall holds 23.9 cu ft of soil. At 22 in it holds 50.2 cu ft, more than twice as much. So build a tall bed when you need the height, not just because deeper sounds better.

When a tall bed is worth it

Height pays off when bending is the problem. UGA says beds for wheelchair access should be 24 in tall, and a bed 36 in off the ground helps you avoid excessive bending. UF/IFAS Extension gives a similar range: at least 6 in high, and up to 24 in for gardeners with mobility challenges.

Our tallest bed is four boards, or 22 in. Tall beds need more bracing, so our plans add cross ties to every bed that is 16.5 in or taller. Cross ties keep the long walls from bowing out under the soil.

How much soil does a raised bed need?

Soil is usually the biggest part of the bill, so size it before you shop. The table below shows the soil our plan engine calculates for common bed sizes. Volumes are the inside volume minus the corner posts and supports, filled to 1 in below the top.

Bag counts assume 1.5 cu ft bags. Bagged soil also comes in 1 and 2 cu ft bags, so adjust the count to the bag you buy. If you order bulk soil by the cubic yard, divide cubic feet by 27. A 4x8 ft bed comes to about 0.9 cu yd at 11 in, 1.4 cu yd at 16.5 in, and 1.9 cu yd at 22 in.

What does a 4x8 raised bed cost?

Here are our estimated material costs for one 4x8 ft bed, bagged soil included. They are estimates from typical US home-center prices, not a quote. Economy uses new copper-treated, ground-contact lumber; Durable uses cedar.

Each step up in depth adds about the same amount again: one more row of boards and about 13 cu ft more soil. That is the best reason to pick the shallowest depth that suits your crops.

How wide and long should a raised bed be?

Width matters as much as depth, because you should never step into the bed. UF/IFAS advises no more than 4 ft wide, since most people can only comfortably reach 2 ft to the center. UGA suggests 4 ft for adults and 3 ft for children.

Our plans cap every bed at 4 ft wide so you can reach the middle from both sides. Length is up to you, but lumber helps decide it. UGA notes that lumber comes in 8, 10 and 12 ft lengths, which is one reason 4x8 ft is such a common size.

Long walls need support

Long walls bow under wet soil. UGA says lumber only 1 in thick needs a vertical support about every 4 ft. Our plans use thicker 2x6 boards and still place a wall support at most every 4 ft along each wall.

What do you put in the bottom of a raised bed?

Most beds need nothing fancy underneath. The bottom just has to let water drain while it holds the soil in place. What you add depends on what you are building over.

• Over lawn or weeds: UF/IFAS suggests a layer of recycled cardboard or several layers of newspaper on top of the grass to suppress it.
• Where gophers dig: the UC IPM pocket gopher guide says to underlay the soil with mesh wire when you build raised vegetable or flower beds. Our plans offer an optional 1/2 in hardware cloth bottom that runs 6 in up the inside of the walls.
• On a hard surface: choose the deeper 16.5 in bed, because roots cannot grow past the base.

Then fill the bed with soil to 1 in below the top. That small gap keeps soil and mulch from washing over the edge when you water.

What wood is safe for a raised vegetable bed?

You have two sound choices: modern copper-treated lumber or naturally rot-resistant wood. UF/IFAS recommends modern pressure-treated lumber, also known as ACQ lumber. The same guide says cedar and redwood resist rot naturally but cost more than treated lumber.

Research supports treated wood for food beds. An Oregon State University Extension study found that treated beds raised soil copper only within 1 in of the bed edge. It found no increase in copper in the vegetables and herbs grown in those beds.

One rule holds no matter which wood you choose. UF/IFAS says not to use railroad ties, or old treated lumber bought before January 2004, for edibles. Our Economy plans use new copper-treated, ground-contact lumber, and our Durable plans use cedar.

How do you plan your raised bed?

You now know how deep a raised garden bed should be for your crops, and the soil each depth needs. Pick 11 in for greens and most vegetables, or 16.5 in for potatoes, root crops and hard surfaces. Then fit the bed to your yard and your reach.

Our free raised bed preview turns those choices into a 3D model before you pay anything, sized with the rules in this guide. You can also compare every style on the raised garden bed plans page before you pick one to build.