how deep should a planter be?
Annuals flowers most often have a shallow root system and grow well in a planter box with an 8-inch depth. Perennials, like bulbs, require a deeper planting box depth.Large bulbs require a planting depth of 8 inches, which means the planter box should allow for the 6 inches needed at the bottom, as discussed earlier, making the depth at least 14 inches.Most smaller bulbs are planted at 3 to 4 inches deep, so they would do fine in planter box with an 8-inch depth.nnuals flowers most often have a shallow root system and grow well in a planter box with an 8-inch depth. Perennials, like bulbs, require a deeper planting box depth.