How Deep Should a Raised Bed Be?
Match it to your crop's root depth. General bands: 6-12in for shallow-rooted crops (lettuce, herbs, strawberries), 12-18in for medium-rooted crops (bush beans, peppers), and 18-24in or more for deep-rooted crops (tomatoes, squash, carrots, potatoes).
The one thing to know: Raised bed depth should be set by your crop's root depth, not a default box height. Shallow-rooted crops (lettuce, herbs, strawberries) do fine in 6-12in of soil. Medium-rooted crops (bush beans, peppers, most herbs) want 12-18in. Deep-rooted crops (tomatoes, squash, carrots, potatoes) want 18-24in or more. A bed shallower than a crop's natural root depth doesn't stop the plant from growing, but it does force roots to spread laterally or hit the bed's bottom sooner, which can affect vigor in hot/dry stretches.
Native soil vs. a hard surface changes the math
A bed placed directly on native soil lets roots extend below the walls into the ground beneath, so a shallower bed can still support a deeper-rooted crop. A bed on a patio, deck, or over landscape fabric that blocks root growth makes the bed's depth a hard limit — size it to your deepest planned crop in that case.
Depth also changes watering frequency
Shallower and elevated (leg-mounted) beds hold less total soil volume and dry out faster, so factor a shorter watering interval into shallower builds. See product picks in First Vegetable Garden Kit.
This page is general equipment/reference information, not planting advice for any specific crop variety.
Frequently Asked Questions
Match depth to your crop's root depth: shallow-rooted crops (lettuce, herbs, strawberries) do fine in 6-12in; medium-rooted crops (bush beans, peppers) want 12-18in; deep-rooted crops (tomatoes, squash, carrots, potatoes) want 18-24in or more. There's no single 'correct' universal depth — it's a function of what you're growing.
Often yes if the bed sits directly on native soil (not a hard surface) — roots can extend below the bed's walls into the ground beneath. If the bed sits on a patio, deck, or landscape fabric that blocks deeper root growth, depth becomes a hard limit and should match the deepest crop you plan to grow.
Yes — shallower beds and elevated beds (on legs) hold less total soil volume and dry out faster, requiring more frequent watering, while deeper in-ground beds retain moisture longer. Factor this into your watering plan, not just your planting plan.
Size the bed to the deepest-rooted crop you plan to include, since a bed can always be over-deep for a shallow-rooted plant but can't retroactively deepen for one that needs more room. Mixed beds commonly default to an 18in-plus depth for this reason.
They suit deep-rooted crops and reduce the need to bend or kneel, but require substantially more fill soil/compost volume to reach the top, which raises upfront cost. Weigh the ergonomic and root-depth benefit against the extra soil volume needed.