Garden of Eatin'

How to Find the Root Depth of Vegetables [Printable Chart]

How deep are the roots of garden vegetables?

What’s the secret to growing a healthy, vigorous plant this season?

Hint: It doesn’t start with what you see above ground.

Root depth is a topic that isn’t often considered when we think about growing in containers, building raised beds, or planning an irrigation system for our garden.

But knowing how deep the roots of your plants reach is one of the most important pieces of the puzzle, especially if you’re working with limited space.

We tend to visualize our plants growing up or out, but before we transplant that first seedling, we need to know how deep they’ll go beneath the surface as well.

Grow tomato plants in 15-gallon containers or larger

Why does root depth and soil depth matter?

Most plants will grow within the space you allow them. They’ll survive with a minimum of soil depth, but they’ll thrive if you give them as much room as possible for their roots to branch out and breathe.

In fact, if you’re a container gardener, this plant study found that simply doubling the pot size allowed plants to grow 43 percent larger.

So forget those 5-gallon buckets for your indeterminate tomato vines — you want them in half-barrel planters (at least 15 gallons) or larger for a good harvest.

Related: How to Grow Tomatoes in Pots Like a Gardening Pro

Just like the saying goes — Feed the soil, not the plants — you want to focus on building strong roots, not just healthy stems and leaves.

Roots that grow deep down in the soil are better able to anchor plants in the ground, maximize their water uptake, and pull in more nutrients and trace minerals.

Know the root depth of your plants before preparing your garden beds

Knowing the root depth of vegetables can help you plan your garden better

If you’re getting a garden bed ready for planting, knowing the root depth of the plants you want to grow can help you determine how extensively to prepare the soil.

For example, shallow-rooted plants like lettuce may do better in soil that’s high in clay and doesn’t drain well.

This may seem to go against common gardening wisdom, but after dealing with heavy clay soil for nearly a decade in my old garden, I’ve realized there’s a time and place for it.

Related: Lettuce… Even in Summer

Since the roots of lettuce and other leafy greens stay close to the surface, they like the extra moisture, tolerate less frequent watering, and only need nutrients in the top 2 to 3 inches of soil, reducing the amount of soil prep you have to do every season — a simple top dressing will work for these types of plants.

On the other hand, heavy-feeding, deep-rooted tomatoes require rich, loamy, well-draining soil, so they benefit from aged compost and plenty of amendments dug down at least 12 inches where the bulk of their root mass is concentrated.

Related: The Secret to Top-Notch Tomatoes Is in This Unlikely Fertilizer

Knowing the root depth of your plants helps you plan the size of raised beds

Root depth can help determine the best height for raised garden beds

If you install raised garden beds over concrete or gravel, you’ll want to know the root depth of the vegetables going in, since they will guide how high you need to build the sides of your beds.

Raised beds built over grass or dirt, however, typically don’t need to be more than the standard 8 to 12 inches in height because the roots can sink into the subsoil (assuming your beds are open on the bottom).

Hydrozone, or group plants with similar root depth together, for more efficient watering

Gardeners in dry climates can use root depth to help with hydrozoning

Root depth is also helpful for hydrozoning, especially if you live in a drought-prone area.

Hydrozoning is the practice of grouping plants with similar water needs together in order to conserve moisture and irrigate more efficiently.

This means you’ll cluster all your shallow-rooted plants in the same bed so you don’t inadvertently overwater them, and group deep-rooted plants together in another bed (on their own irrigation line) so you don’t underwater them.

Hydrozoning also comes in handy if you like to interplant your crops by growing beneficial flowers and herbs among your vegetables, or planting quick-growing crops (like radishes) between rows of long-season crops (like broccoli).

Cucumber roots grow deep as well as laterally

It’s not just how deep, but how wide

While we usually think of roots as growing downward, it’s important to remember that roots grow laterally as well, and to account for that in our garden beds and containers.

For example, a cucumber plant sends down a single tap root 3 to 4 feet deep. The majority of its roots, however, extend outward about 2 feet and are concentrated just below the soil surface.

You’ll also want to factor in the final height of the mature plants, as insufficient soil volume in a container can make them too top-heavy.

Always follow the spacing recommendations on your seed packets and plant tags to ensure you give your plants plenty of room to grow.

Mint is a shallow-rooted plant

Soil depth requirements for common garden vegetables, fruits, and herbs

Some vegetables, like spinach and spring radishes, have very shallow roots and don’t need more than 4 to 6 inches of soil to grow successfully. But the smaller the planter, the more often you’ll need to water.

Just keep in mind there’s no need to plant these varieties in containers deeper than 12 inches, as you’ll only be wasting soil and space.

On the other hand, plants like lemongrass (which clump and multiply rapidly) and tomatoes (which grow adventitious roots along their stems) will grow as large as you let them, so giving their roots more room to roam will produce a more robust harvest.

Use the chart below to help you find the root depth of common vegetables and herbs, plan and prep your garden, and determine how deep your raised garden beds or planters should be.

Winter radish is shallow-rooted

Garden Betty’s Vegetable Root Depth Chart

Download printable root depth chart
Shallow Rooting
(12 to 18 Inches)
Medium Rooting
(18 to 24 Inches)
Deep Rooting
(24 to 36+ Inches)
ArugulaBeans (fava)Artichokes
BasilBeans (pole)Asparagus
BlueberriesBeans (snap)Beans (lima)
Bok choyBeetsBurdock root (gobo)
BroccoliCantaloupesCardoon
Brussels sproutsCarrotsOkra
CabbageChardParsnips
CauliflowerCucumbersPumpkins
CeleriacDaikonRhubarb
CeleryEggplantSquash (winter)
ChivesMuskmelonsSweet potatoes
CilantroPeas (shelling)Tomatoes
Collard greensPeas (snap)Watermelons
CornPeas (snow) 
EndivePeppers (hot) 
FennelPeppers (sweet) 
GarlicRosemary 
GingerRutabagas 
Jerusalem artichokesSage 
KaleSquash (summer) 
Kohlrabi Turnips 
Leeks  
Lemongrass  
Lettuce  
Mint  
Mustard greens  
Onions  
Oregano  
Parsley  
Potatoes  
Radishes (spring)  
Radishes (summer)  
Radishes (winter)  
Scallions  
Shallots  
Spinach  
Strawberries  
Tarragon  
Thyme  
Turmeric  
Download printable root depth chart
Strawberry plants do well in wide, shallow containers

More ways to prepare for planting this season:

This post updated from an article that originally appeared on February 27, 2019.

About Author

I'm a plant lover, passionate road-tripper, and cookbook author whose expert advice and bestselling books have been featured in TIME, Outside, HGTV, and Food & Wine. The No-Waste Vegetable Cookbook is my latest book. Garden Betty is where I write about modern homesteading, farm-to-table cooking, and outdoor adventuring — all that encompass a life well-lived outdoors. After all, the secret to a good life is... Read more »

3 Comments

  • Frank K
    November 15, 2020 at 12:55 pm

    Easy to read with full of good information. Thank you!

    Frank

    Reply

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