What depth is optimal for vegetable roots?
Written by
Benjamin Miller
Reviewed by
Prof. Charles Hartman, Ph.D.More than many gardeners understand, the root depth of a vegetable will determine its success; I have seen clients with shallow beds grow carrots that fork and tomatoes that stun in growth, while clients that respected the root depth guideline of a vegetable grew 3x more than those in shallow soil. Most crops require 12-18 inches of loose, nutrient-rich soil to grow, but variations exist. One way to determine if you have enough soil is to measure the height of your bed.
Leafy Greens
- Examples: Lettuce, spinach, arugula
- Depth: 8-10" for rapid growth
- Tip: Use shallower beds for baby greens
Fruiting Plants
- Examples: Tomatoes, peppers, eggplant
- Depth: 14-16" for strong root anchors
- Tip: Add compost to lower 6" at planting
Root Vegetables
- Examples: Carrots, parsnips, daikon
- Depth: 18"+ for straight development
- Tip: Remove rocks below 12" to prevent forking
Using shallow beds wastes time and effort. A client of mine had a 10" bed that performed well for lettuce but struggled to produce peppers. I suggested raising the shallow bed. Consider using stackable beds for carrots or other root crops, and you can always add a 6" extension as the plants grow. You will always want to leave 2" below the rim of the beds to prevent washout should you have rain.
Check the soil depth every year. Use a metal rod, push it down until it won't go any deeper, and if there is a hardpan layer under 12", it needs to be broken up with a broad fork. One gardener's carrot yield improved by 70% after we tilled his compacted clay soil to 18". More depth without aeration is just extra depth where roots can't grow.
Read the full article: 7 Expert Tips for Perfect Raised Bed Soil Every Time
