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Interplanting Vegetables: Root Depth, Plant Height

Crop interplantingInterplanting is a growing method that will allow you to fit more vegetable plants in a single planting bed. It is a way to increase your crop yield. Interplanting is also called intercropping.

Interplanting is often used in intensive vegetable gardening where an effort is made to use all available space in the growing area–the counter point to single row planting which requires the most cropping space since the space between rows goes unplanted. (In intensive gardening you can space plants individually equidistance apart or in wide rows–several plants across a row to as much as 4 feet wide.)

There are several ways to interplant your crops. You can grow fast-maturing plants, such as radishes, between slower growing ones, say chard. The radishes will be ready for harvest before the chard begins to mature and requires more space to spread out. This way of interplanting borders on succession cropping–bringing one crop to harvest after another keeping the planting bed productive all season.

You can also interplant crops with different growing habits, tall crops near short ones, or deep-rooted with shallow-rooted. Crops interplanted by growing habit can be set equidistant according to their size (height and breadth or root depth) at maturity; or they can be planted in their own alternate rows in a wide bed.

Interplanting requires planning. You need to know the days to maturity for each crop and its height and breadth at maturity or its root depth at maturity. Do some planning on paper once you have decided on the crops you will be growing this season.

To assist your planning here are two charts that might help: one for plant height at maturity, one for rooting depth (For additional information on vegetable crop root development, see the 1927 book “Root Development of Vegetable Crops” by John Weaver of the University of Nebraska.):

Root Depth

Shallow Rooting (18 to 36 inches)
Medium Rooting (36 to 48 inches) Deep Rooting (more than 48 inches)
Broccoli  Beans, snap  Artichokes
 Brussels sprouts  Beets  Asparagus
 Cabbage  Carrots  Beans, lima
 Cauliflower  Chard  Parsnips
 Celery  Cucumbers  Pumpkins
 Chinese cabbage  Eggplant  Squash, winter
 Corn  Peas  Sweet potatoes
 Endive  Peppers  Tomatoes
 Garlic  Rutabagas
 Leeks  Squash, summer
 Lettuce  Turnips
 Onions
 Potatoes
 Radishes
 Spinach

Plant Height

Tall Medium Short
 Beans, pole  Anise  Basil
 Broccoli  Artichokes  Beets
 Corn, sweet  Broccoli  Borage
 Fennel  Brussels sprouts  Cabbage
 Mustard  Lemon balm  Caraway
 Okra  Beans, bush  Carrots
 Peas  Broccoli  Cauliflower
 Sunchokes  Brussels sprouts  Celery
 Tomatoes  Cardoon  Chervil
 Chard  Chives
 Chinese cabbage  Corn salad
 Collards  Dandelion
 Coriander  Endive
 Cucumber  Garlic
 Dill  Kale, dwarf
 Eggplant  Kohlrabi
 Hyssop  Leeks
 Kale, curled  Lettuce
 Lavender  Onions
 Marjoram  Parsley
 Peas, dwarf  Parsnips
 Peppers  Radishes
 Potatoes  Rutabaga
 Pumpkins  Savory
 Rhubarb  Thyme
 Sage  Turnips
 Spinach
 Squash
 Sweet potatoes

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16 Comments

    • You will find root depths for all vegetables in The Kitchen Garden Growers’ Guide by Stephen Albert–available at Amazon. To answer your specific questions: pepper plant fibrous roots generally reach down about 8 inches; eggplant roots about 18 inches to 2 feet; tomatoes about 18 inches; onions are shallow rooted, never more than 12 inches. At minimum you will want a 5 gallon nursery container; larger would be better.

      • The root depths you are quoting are minimums — tomatoes are considered deep rooted vegetables and their roots can exceed 3′.

        Raised pots — is this just pots, or is this a pots sitting above the soil ?
        Is there an option to cut the bottom out of the pots to allow the roots to go deeper if they should chose to. I had decent success with pots that were about 16″ tall with no bottoms. I worked my soil as best I could, ammended it (compost/manure/aged shredded bark mulch) the “sank” the pots about 6″ into the ground (10″ exposed above ground) and filled the pots with my soil mix (1/3 soil, 1/3 compost. 1/3 aged shredded bark mulch) … I did O.K.

        The big problem is the roots get too hot (10″ above ground portion of the pot subject to “cooking conditions”) — consider planting something in the ground shallow rooted around the pots to keep the pots cool — or maybe build a bark mulch mound around the pots to keep the sun off of them.

        • Thank you for this comment and tip. Yes, tomato roots in soil without the obstructions of clay or pebbles can grow 7 feet deep and deeper, particularly in regions that are close to the tomato’s subtropical origins. Using a bottomless pot above the native soil is akin to growing in a raised bed. The soil in containers and raised beds warm more quickly and stay warm longer than the native soil. Insulating the pot or raised bed from atmospheric warmth and chill will keep the soil in the container at closer to a constant temperature. Insulation could include mounding soil, compost, mulch, straw up around the pot or raised bed or using a man-made insulation.

    • Watermelon roots will commonly grow to 15 inches deep; muskmelon roots to 18 inches deep. The spread of the root system can be as extensive as the vine growth–12 to 18 feet across. The most thorough study of vegetable root development was published in 1927 by John Weaver, an agronomist at the University Nebraska; his book was called Root Development of Vegetable Crops.

    • Mature penstemon can grow to 24 inches deep or more; however penstemon will easily survive with roots to a depth of 6 to 12 inches. Campanulas are more shallow rooted than penstemon–to a depth of 6 inches at maturity.

    • All vegetable plant roots will spread as they seek moisture and nutrients. If you are providing moisture and nutrients, a plant may be able to sustain itself in the unnatural environment you are giving it. In optimal soil conditions, researchers have found that sweet corn roots are shallow to about 3 feet and spread to about 7 feet; lettuce has a taproot that grows to about 4 feet deep and feeder roots spread to about 4 feet; beets send down a taproot to 10 feet and feeder roots to 58 feet wide; carrot taproots can grow to 8 feet deep and feeder roots to 6 feet wide. Again, these are optimal soil conditions.

  1. Nice website. Helpful. I think it would be helpful if you also published in your tables the average height of the various vegetables, instead of short, medium, and tall. I am looking to buy some black net tunnels, and I see yours are 30cm high. I only want black as it blends in better and you can still see the veggies well. I have two other black net tunnels and they are about 35 to 40cm tall depending how you put them in the ground. Before I order I am looking to see about plant height. Do you have any taller tunnels in black? Hope you can appreciate my problem. Feel free to let me know with private message. Thanks!

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