Lessons from Roots: Why Our Plants Do Best in Wide Beds That Are Loosened Deeply

We understand that our garden plants need rich, deep, well-drained, well-loosened soil that’s full of organic matter, but how deep and how loose is ideal? Why so deep? And why is planting in beds so important?

Nothing illustrates the need for wide, deeply loosened planting beds better than a look at the meticulously made drawings of the roots of common garden plants at different stages in their lifecycles made by John E. Weaver and William E. Bruner.

As gardeners, the love for soil is in our bones. Working it, its smell and feel in our hands, its redolence as it warms back to life each spring—all fill our hearts in ways we can never express, just as its smell after summer rains soothes our souls as our faces light in smiles unbidden. Yet, we don’t often consider the full extent of our soil, especially those areas below the top few inches with which we regularly interact.

The same could be said for our plants. As gardeners, we clearly care deeply about them. A large part of gardening for us is the joyful glorious gifts they bestow upon us, in beauty and wonder as much as produce. That moment in early summer when enough of their marvel catches our eye that we find ourselves sweetly pulled from our garden chores to sit in a path, soaking in their simple majesty, awed by their profuse proliferation in an area that only a couple of short months ago had been merely a bare hopeful patch of earth, elevates our souls in many ineffable ways. Still, for all of that appreciation, we tend to spend most of our time focusing on their growth above the soil. In truth, many gardeners harbor only a very vague sense of the world beneath it, often thinking their plants’ roots aren’t much bigger than the comparatively little sprigs left broken off from the rest of their massive systems when pulled up in the fall.

It makes sense. Other than these sprigs of roots—mere hints of the massive systems from which they broke—and the top few inches of soil we regularly work, this world is largely hidden from us. To gain a better understanding of this world beneath our plants’ foliage, let’s first look to the expert gardeners who understand the importance of the depths of their soil so well that improving it has become the core of their work and then look to the researchers who painstakingly illustrated the massive depth and breadth of our plants’ roots.

The Green Thumb Perspective

Although there is a myriad of reasons why the green-thumbed gardeners of the world have such astounding success, the productivity of their plants always starts with their overarching perspective. The plethora of skills they possess for seemingly every aspect of gardening actually emanate directly from their different perspective on gardening as a whole. One can focus on the discrete skills they possess—the pages of this website are filled with them—but gaining their perspective is much more valuable. Since it forms the foundation for all of one’s gardening actions and problem-solving, it provides gardeners with a masterful set of skills and solutions.

While their unique views on other “big secret” fundamentals like sunlight and water are also important, especially green-thumbed gardeners’ views of their soil and their plants’ roots arguably form the largest and most important part of their potent and productive perspective. While especially green-thumbed gardeners also focus on their plants’ above-ground growth just like other gardeners, they put an even greater amount of focus and energy into their plants’ roots by attending to the quality and looseness of the surrounding soil.

Green-thumbed gardeners turn the focus on above-ground growth on its head for good reason. They know it’s where they can have the most profound impact. The authors of probably the most thorough and meticulous study of garden plants’ roots mentioned above make the point perfectly: “In both field and garden the part of the plant environment that lies beneath the surface of the soil is more under the control of the plant grower than is the part which lies above. He can do relatively little toward changing the composition, temperature, or humidity of the air, or the amount of light. But much may be done by proper cultivation, fertilizing, irrigating, draining, etc. to influence the structure, fertility, aeration, and temperature of the soil.” Students of roots as they were, they knew what really makes a difference to our plants.

Knowing this, green-thumbed gardeners provide their plants’ massive root systems with as much loosened soil area as possible. This means adding organic matter to and loosening the soil as deeply as realistically feasible—so plant roots have plenty of rich, loosened soil into which they can grow deeply—and planting in wide beds—so plant roots have loosened soil into which they can expand broadly.

Necessary paths and the required labor of digging deeply are limiting factors. Plus, as we’ll see, our plants’ roots outgrow even our best efforts. Green-thumbed masters, however, mitigate these impediments by providing as much loosened soil space as they feasibly can—typically, this means beds between four and five feet wide and soil loosened one-to-three feet deep—and making efforts to keep that soil as loose as possible (see Layout and Spacing, Cover Crops, and Mulching) to foster root proliferation throughout their soil.

Common Garden Plants’ Roots

To truly understand the underground world of our gardens and the need for wide, deeply-loosened beds, however, we must gain a deeper understanding of our plants’ roots. Knowing their true depth and breadth moves us from focusing solely on the above-ground growth. Instead, as soon as we understand the extent of their root systems, we inherently understand what our plants need and why. We also gain a much greater understanding of soil as a planting medium, not just dirt, one in which we benefit our plants greatly by providing deep, rich, well-loosened soil full of organic matter. Such soil allows plants’ roots to grow freely, making it much easier for these amazing root systems to explore outward and find the wonderful nutrients and water we’ve put there for them. 

---

Sweet Corn

Only 16 days after planting, while the nascent tops are only seven inches tall, sweet corn roots are already 18 inches long and heavily branched. Not even subtracting several days for germination, they’ve grown more than an inch a day! 

By midsummer, less than two months (55 days) after planting, with the plants four-and-half feet tall and their tassels half out, the roots have penetrated a massive area six feet in diameter. Most of the deeper roots at this stage are closer to three-feet deep, but one has penetrated to four-feet deep. Closer to the surface the roots have branched into dense networks. Up to two-feet deep, this network is quite dense and extensive, and “the surface soil,” the authors note, “especially the first 10 inches and within a radius of 9 inches from the crown, was [is] filled with a dense tangle of roots, a network so complex and so profuse that there seemed [seem] actually to be more roots than soil.” The authors of the study say there’s no way they could accurately represent all of the roots in a drawing, so the ones pictured are just the “principal features.”

In late August, with plants averaging 5.3 feet tall, the roots (not pictured) haven’t extended much more in diameter, but they’ve extended their overall depth and the depth of their dense network greatly. Numerous roots now extend to 60 to 68 inches deep (five to over five-and-half feet!), and they’ve filled in their denser network to 50 inches deep. The authors note, “Thus, over 180 cubic feet of soil are occupied by the roots of a single plant.”

The authors also note a general, instructive rule they observed about the size of the roots in relation to the above-ground plant, “Briefly, sweet-corn roots extend laterally more than half as far as the stalk extends upward, and the root depth is equal to the height of this rather imposing vegetable crop.” In other words, the roots are as deep as the plant is tall and extend in a radius more than half of its height, making the diameter of its root system just more than its height as well—a good general rule to remember in the garden when thinking about the size of the roots below the surface.

---

Peppers

Just three-and-a-half weeks after transplanting, pepper roots are already spreading vigorously.

Two weeks later, with the plants eight-inches high and flower buds just starting to appear, the roots are quite extensive, completely filling “the surface foot of soil to 18 inches on all sides of the plant” and extending two feet deep.

In mid-July, eleven weeks after transplanting, with plants 20 inches tall, the pepper roots have grown four feet deep and extend in a six-foot diameter. The roots are so extensive and dense at this point that the authors state that they could only accurately represent one-fourth of them! We have to imagine the rest. Plus, this was mid-July. Pepper plants and their roots keep growing vigorously until finally slowed by cold weather and eventually killed by a hard freeze in the fall. It’s common, for example, for a pepper plant grown in a double-dug bed to reach 40 inches tall, nearly twice the height of the plants that have one-quarter of their roots drawn above. The roots of these late-season plants weren’t drawn or described by the authors, but, supplying the massive branching leaf area of these late-season monsters, heavily laden with fruit, we can only imagine they are much more extensive and much deeper than those drawn above.

---

Tomatoes

Though tiny whispers compared to the behemoths they’ll become, just three-and-a-half weeks after transplanting, when above-ground growth is eight-to-twelve inches tall, tomato roots reach over two-feet deep and almost four feet in diameter. 

A month later, on July 11, with plants averaging 19 inches tall, the roots form a vast network, spreading in all directions, seven feet in diameter and four-feet deep.

Like peppers, however, tomatoes grow until they’re killed by frost in the fall, their roots continuing their expansive growth to mirror and provide for the explosion of foliage above, becoming massive, dense networks, far beyond what is pictured above. The authors of this particular study did not draw the roots of these plants, but they did describe them.

By early August, the above-ground growth on the plants studied was four feet in diameter and contained 400-500 leaves per plant and abundant fruit. They found the roots at this stage to have utterly filled the spaces between the roots that were present in the deeper soil eight weeks after transplanting (i.e. those shown in the representative drawing of roots eight weeks after transplanting shown above). They describe this dense branching of the roots up to three-and-half feet deep and even farther by stating, “Thus a soil volume with a surface area of at least 80 square feet and a depth of 3.5 feet–280 cubic feet of soil–was thoroughly ramified. Many roots extended more widely (maximum, 5.5 feet) and some even penetrated more deeply.” Two hundred eighty cubic feet filled with roots?! Damn! That’s an area of extremely dense roots 10 feet in diameter, three-and-a-half-feet deep! And some roots have ventured even farther by this point, making the farthest extent their diameter 11 feet! The authors also elaborate on “some even penetrated more deeply,” noting that some roots went as deep as four-and-a-half feet deep.

Again, however, this was early August. Tomatoes are far from done growing by then. Tomatoes planted in freshly double-dug beds commonly reach heights of seven-to-eight feet by the end of their growing season. Imagine those root systems!

---

Cauliflower (and likely Broccoli)

Eight weeks after transplanting, when plants are about a foot tall, cauliflower roots have formed an extremely dense mat a foot deep and two-feet in diameter, with some dense clusters extending up-to-three-feet deep and five feet in diameter. 

Three months after transplanting, when plants are two-feet tall with a spread of two-and-a-half feet and harvestable heads, their root systems, still five feet in diameter, have penetrated five-feet deep and have filled out the soil in a roughly cone-shaped profile with such a dense cluster of roots that the authors of the study stated that it was “quite impossible to show the complete degree of branching in the most carefully executed drawing.” Broccoli, so closely related, was not studied, but it is likely similar, as is cabbage, which was studied.

---

Others of Note

Swiss Chard

Midsummer Swiss chard penetrates more than six-feet deep, with a diameter of almost nine feet.

Lettuce

Often thought to be shallowly rooted, mature lettuce has roots in a diameter of a little over three feet penetrating seven feet deep.

Spinach

At ten weeks, spinach has roots with a diameter of three feet penetrating four feet deep. 

Others

Others studied are also illustrative. For example, many of the cucurbits (squash, pumpkins, cucumbers) are wide-ranging but not very deep, making their traditional planting method a superb one for them.

---

Lessons

While not all garden plants have root systems as deep as peppers, tomatoes, and the larger brassicas, many still have root systems that are much larger than we think. As such, our garden plants’ roots are one of our best teachers, showing us the benefits of loosening and providing richness through added organic matter to deeper levels of the soil than is traditionally provided, especially for those plants that really benefit from it (like peppers, tomatoes, and the larger brassicas).

Even more importantly, knowing the depth and breadth of our plants’ roots helps us understand our role as gardeners as builders of our soil. It makes us realize the truth of the trenchant insight that our soil is the one area over which we have the most influence. Sun and water are provided by nature free of charge (and labor) and are easy enough to fix if they’re absent (e.g. site garden in a sunnier location, water when dry). Aside from cutting down a few trees if we decide it’s worth it, there’s not much else we can do. Soil, however, is different. Also initially provided by nature free of charge, it can, instead, be worked to improve it when it’s poor and to make it even better when it’s good but not quite as rich, full of organic matter, well-drained, well-loosened, and deep as we, and our plants, would ideally like. 

Our next step, then, is learning how to improve each of these aspects of perfect soil.

---

About the Authors of the Original Work

John E. Weaver and William E. Bruner, both professors at the University of Nebraska while undertaking this research, made detailed drawings of meticulously unearthed garden plant roots. All of the above drawings and quotes are from their original work which can be found in their entirety here.

The researchers had gardeners in mind when they did their study, stating, “It [this study] is designed for the use of investigators and producers as well as to meet the needs of ‘students [sic] of vegetable gardening.” And they knew exactly the importance of the world they were uncovering: “The lack of exact knowledge and the frequently grossly inaccurate statements regarding the nature and extent of the root systems of vegetable crops have shown the need for intensive study.” “Thus, a thorough understanding of the roots of plants and the ways in which they are affected by the properties of the soil in which they grow is of the utmost practical importance.”

In Their Own Words

These researchers are acutely insightful in their discussions of the importance of their published findings, measurements, and drawings for gardeners. While an excerpt or two of these quotes were used earlier in the text, some readers will be interested to read these authors’ remarks from their introduction in full and in context.

 “[I]t’s is not surprising that from time immemorial extended observations and, later, experiments have been made upon the aerial growth of crops under varying conditions. In fact an almost bewildering array of literature has resulted. But quite the converse is true of the underground parts. The root development of vegetable crops has received relatively little attention, and indeed accurate information is rarely to be found. The roots of plants are the least known, least understood, and least appreciated part of the plant. This is undoubtedly due to the fact that they are effectually hidden from sight. Notwithstanding the extreme difficulty and tediousness of laying the roots bare for study, it is not only remarkable but also extremely unfortunate that such investigations have been so long neglected.”

They continue, “The student of plant production should have a vivid, mental picture of the plant as a whole. It is just as much of a biological unit as is an animal. The animal is visible as an entity and behaves as one. If any part is injured, reactions and disturbance of the whole organism are expected. But in the plant, our mental conception is blurred by the fact that one of the most important structures is underground….

“In both field and garden the part of the plant environment that lies beneath the surface of the soil is more under the control of the plant grower than is the part which lies above. He [or she] can do relatively little toward changing the composition, temperature, or humidity of the air, or the amount of light. But much may be done by proper cultivation, fertilizing, irrigating, draining, etc. to influence the structure, fertility, aeration, and temperature of the soil. Thus, a thorough understanding of the roots of plants and the ways in which they are affected by the properties of the soil in which they grow is of the utmost practical importance….”