3x6 Raised Bed Onion
A complete plan for soil, plant count, and yield range for onion in a 3x6 raised bed.
Quick answer
For a 3x6 bed at 12" depth: soil ≈ 18 ft³ (≈ 0.667 yd³).
With 4" spacing: 162 onion plants.
Yield range (raised bed): 51.0–119.1 lb (typical ≈ 85.0 lb).
Worked example
Soil: 6×3×(12/12) = 18 ft³ (≈ 0.667 yd³).
Bags: 2 cu ft → ceil(18/2) = 9, 3 cu ft → 6, 1.5 cu ft → 12.
Plants: floor((6×12)/4)×floor((3×12)/4) = 162.
Why these numbers vary
Real results vary by variety, trellising, fertility, watering, temperature, and how aggressively you harvest. Treat this as a planning range—not a promise.
Spacing note
This page uses the dataset spacing (4"). If you plant tighter or wider, switch to Custom spacing in the calculator.
FAQ
How many onion plants fit in a 3x6 raised bed?
Using 4" spacing and a floor grid, you can fit about 162 plants.
Do I need to buy extra soil?
Often yes. Soil settles, especially mixes with compost. Many gardeners buy 5–15% extra.
Is 12 inches of soil depth enough?
For most vegetables it’s a good baseline. Deep-rooted crops may benefit from more depth or looser subsoil.
Does trellising change the spacing?
Yes. Trellised crops can sometimes be spaced tighter. Use Custom spacing if you have a proven system.
Why is yield shown as a range?
Yield depends heavily on variety, climate, fertility, pest pressure, and season length.
Sources
- Dataset: crops.json (PlantYields v1.1.0)
- See notes on the crop guide page for variety guidance.