By Azura · Updated May 2026 · Raised Garden Hub is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you.
Depth is the raised-bed number people most often get wrong. Too shallow and roots hit the bottom; too deep and you pay for soil you don’t need. Here’s the simple answer.
Depth by crop
| Depth | Best for |
|---|---|
| 6–8 in | Lettuce, spinach, herbs, radishes |
| 12 in | The all-rounder — most vegetables |
| 14–18 in (18 preferred) | Tomatoes, peppers, broccoli |
| 18 in+ | Carrots, parsnips, potatoes |
When in doubt, 12 inches is the safe default for a mixed vegetable bed.
Does the bed sit on soil or a hard surface?
- On open ground: roots can grow into the soil below, so the bed itself can be a bit shallower (8–12 in works for a lot).
- On a patio, deck, or concrete: there’s no soil below, so go deeper — 12–18 in minimum — because all the root volume has to fit inside the bed.
Why deeper isn’t always better
Every extra inch of depth multiplies the soil you must buy. A 4×8 bed at 18 inches needs about 50% more soil than at 12 inches. For greens and herbs, that’s money wasted.
Save money on deep beds
If you do need a tall bed, don’t fill it all with premium mix. Use cheap fill methods for the bottom third and a good soil mix on top.
Not sure on width and length either? Our best size guide has an interactive advisor and a soil calculator.