Root Depth for Vegetables

Standard

Ill.: Park Seed

I receive a lot of email from readers putting in raised bed gardens, but who seem doubtful that you really need to fill the whole thing from the base to the summit with top-quality soil. They don’t seem to realize just how deep vegetable roots can go. I have beds 2 feet (60 cm) high filled with the best soil I could buy locally and I find that scarcely enough, at least, not when you want productive vegetables rather than a wimpy crop.

In a raised bed, you want rich, well-draining soil from bottom to top. Photo: The Gardening Channel With James Prigioni

Some people even want to put a layer of gravel in the bottom. Gravel! Can you believe that? Or fill it with so-called “black earth” (actually black peat): inexpensive, for sure, but just about the worst soil amendment on the market. Yikes!

I think it might help to see just how deep some vegetable roots grow, as the chart below shows. Maybe you can skimp when it comes to herbs (most are shallow-rooted and not particularly needy of rich soil), but when it comes to vegetable gardening, you always want the best soil you can get and as deep as possible.

Soil Depth Requirements for Common Garden Vegetables

Shallow Rooting
12″–18″ (30–45 cm)
Medium Rooting
18″–24″ (45–60 cm)
Deep Rooting
24″–36″+ (60–90 cm+)
ArugulaBean, dry Artichoke
Basil Bean, fava Asparagus
Bok Choy Bean, pole Bean, lima
Broccoli Bean, snap Comfrey
Brussels sprouts Beet Horseradish
Cabbage CarrotOkra
Cauliflower ChardParsnip
Celery CucumberPumpkin
Chinese cabbage Eggplant (aubergine)Rhubarb
ChivesKaleSquash, winter
Cilantro (coriander) MelonSweet potato
Collards PeaTomato
Corn Pepper Watermelon
Endive Rosemary
Fennel Rutabaga
Garlic Squash, summer
Jerusalem artichoke Turnip 
Kohlrabi  
Leek   
Lettuce   
Mache   
Mint   
Onion   
Oregano   
Parsley  
Potato   
Sage  
Savory   
Spinach   
Strawberry   
Tarragon   
Thyme  

You still want to fill your raised bed with third-quality soil? Or black earth? Or gravel? Go ahead, but don’t say I didn’t warn you!