Soil depth guidelines by crop type

Matching soil depth to crop root requirements prevents wasted soil volume and ensures adequate growing space. Shallow-rooted crops (6-8 inches minimum): lettuce, spinach, radishes, green onions, most herbs, strawberries. Medium-rooted crops (10-12 inches minimum): beans, peppers, cucumbers, broccoli, cabbage, Swiss chard, beets. Deep-rooted crops (16-18 inches minimum): tomatoes, squash, carrots, parsnips, potatoes, corn, watermelon, eggplant. For beds shorter than 10 inches placed on the ground, roots will extend into native soil below (beneficial in most cases). For beds on hardscape (concrete, asphalt), the full root depth must be within the bed. A universal safe depth for most vegetables is 12 inches, though 18 inches accommodates virtually all common garden crops. Deeper soil also provides better moisture buffering, requiring less frequent watering. Always account for 1-2 inches of settling in the first season when calculating fill depth. Overfilling by 10-15% compensates for initial compaction.