Root Depth: What Size Should The Container Be?

Whether you're using containers, building raised beds over a surface that prevents root growth, inter-planting, or wondering how deep to prepare the soil, knowing the general root depth of a plant can be very helpful information - especially important for those of us who work with limited space.
 
Should you be dealing with limited space, keep in mind you don't really need to accommodate every possible inch of root growth, only where the plant's roots are the most heavily concentrated. For example, some of a tomato plant's roots may go down 4 feet, but most of the roots are no deeper than 2 feet, so the tomato will grow fine in a 2 foot deep container.
 
Shallow Rooting
-Maximum depth of 12-16 inches, doesn't need more than 12 inches
Arugula
Blueberries - Roots are very shallow, but grow about 2 feet wide
Broccoli
Bok Choy
Brussels Sprouts
Cabbage
Cauliflower
Celery
Collard Greens
Corn - Shallow, but roots spread about 20 inches wide
Jerusalem Artichoke
Kale
Kohlrabi
Leeks
Lettuce - Very shallow, can be grown with only 4-6 inches of depth
Napa Cabbage
Onion
Potatoes
Radish - Very shallow, can be grown with only 4-6 inches of depth
Spinach - Very shallow, can be grown with only 4-6 inches of depth
Strawberries - Roots are very shallow, but grow about 1 foot laterally
Most Herbs (basil, chive, cilantro, mint, oregano, parsley, tarragon, thyme)
 
Medium Rooting
-Maximum depth of 16-24 inches, doesn't need more than 16 inches
Beans - Roots grow about 10 inches wide
Beets
Carrots
Cantaloupe
Chard
Cucumber - Roots grow about 20 inches wide
Eggplant
Peppers
Peas
Rosemary
Rutabagas
Sage
Squash, Summer
Turnips
 
Deep Rooting
-Maximum depth of 36+ inches, requires at least 24 inches
Artichoke
Asparagus
Parsnips
Pumpkins
Rhubarb
Squash, Winter
Sweet Potatoes
Tomatoes
Watermelon
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