A recent question from a fellow gardener who is waiting for spring concerned the root depth of vegetable plants. He is building a raised bed to improve the growth of certain vegetable plants he hasn’t had success with in the past. Specifically, he wanted to be sure that he had enough soil depth for positive and appropriate root growth.
Of all the aspects you can control in your gardening beyond the type of plant, the aspect most under your control is the soil environment. While we plant to take advantage of the best above-ground conditions, those conditions, including temperature, humidity, air composition and amount of light, aren’t in our control as much as our soil. Since we can modify the soil but don’t always do so, it’s lucky for us that plant roots can adapt, to varying degrees, to their environment. Considering our desire to eat, it’s especially good that vegetables in particular have shown an ability to adapt to a wide range of climates and soils.
To start, I suggest visualizing in your mind the plant as a whole, including the root system. When you can “see” the whole plant and not just the above-ground part it can lead to a better understanding of the plant’s needs as a whole.
For instance, consider the bean plant — in this case, the kidney bean. Research shows the plant’s roots can reach a spread of 30 inches or more and the “tap” root can extend to a 3-foot depth. This is similar to other beans but can vary depending on the type of bean. If you could look at the plant and root system from the side, you would see the bulk of the root mass spreading out in the top 8 to 12 inches, with a taproot trailing down. As time progresses some of those upper roots also start trailing down, with more feeder roots spreading out.
With another favorite, the tomato, the roots from an average sized tomato can spread out 2.5 feet from the base and down to a depth of more than 3 feet. Again, the largest mass of roots is in the top foot or so of soil, but there’s always a good percentage that grow deeper and peppers and eggplants can show similar root structures. Plants with smaller above-ground growth such as beets and spinach can have roots spreading out 1 to 2 feet, but they often also have fairly deep roots due to a main root that reaches deeper depths.
All of these spreading roots have some branching, with the smaller fibrous roots taking up the nutrients and moisture. As the plant grows the mass of roots nearer the surface uses up nutrients, and water needs increase so that by mid-summer some of those upper roots, as they continue to grow, start taking a more downward path.
Research shows roots absorb nutrients and water at all depths, admittedly more from the upper portion of the soil because that’s where the majority of roots are. As the crop reaches maturity, the deeper roots provide an increased share of the nutrients and moisture.
As a gardener, you should want the best root distribution, which includes depth and spread. In addition, unless you are planning to build a really high raised bed it’s likely some of the plant’s roots will grow down into the existing soil. What’s important is whether the soil is hospitable to the roots throughout and if there is anything that would hamper growth.
The bottom line is that it’s the top portion of the plant that is of most interest and it’s pretty common for the roots to be seldom considered but very critical to the positive growth of any plant. So watch your water and nutrients and enjoy the top plant portion of whatever you are growing, but always consider what you can do to help out the roots.
Thought for the day: “To be a successful farmer one must first know the nature of the soil.” —Xenophon
Previous articles are available at The Times-Independent website, www.moabtimes.com. Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at firstname.lastname@example.org.