Deep

Most gardeners add richness and organic matter with soil amendments and till them in, attempting to create ideal soil, but tillers only incorporate these amendments and loosen the soil about six-to-eight inches deep. Our garden plants, however, actually benefit greatly from our soil being improved and loosened much, much deeper than that.

Aside from growing soil, the thing most people don’t “see,” and that perhaps even some green-thumbed gardeners don’t realize, is the sheer volume and size of their plants’ roots and how incredibly deep these grow. People just seem not to comprehend how extensive plants’ root systems are. Lying under the soil and out of sight, we just don’t think of all that’s going on under the surface. 

The horticultural master he was, my father always tried to impress upon his children the importance of this world we couldn’t see. He would regularly ask us to consider that root systems are typically as large below the surface as all of the growth that can be seen above it. That was his general rule. And with it in mind, he’d advise clients, “For a one-dollar tree, dig a ten-dollar hole.” His general rule is just a rough guide, but take it to heart: Walk around your outdoor spaces looking at your plants from this perspective, that there is as much below ground as above it. Think of the root systems of your garden plants and those massive trees!

Luckily we don’t have to just imagine, however. 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. It turns out my dad was on the right track but had grossly understated the case: Plants’ roots are actually much deeper and wider than the spaces we make for them, and what’s below ground is often much, much larger and more extensive than the growth above ground.

The root systems of our garden plants are incredible. They are dense and deep, routinely reaching over four feet deep—making it clear why everything we do for our plants and soil must also be done deeply.

Nothing illustrates this point, and several other points in these pages about soil, better than a look at several of the drawings Weaver and Bruner and their graduate students made of the roots of common garden plants at different stages in their lifecycles.

Next, we turn to them in more detail. Those pictured above are just a hint of their extent.