Understanding Roots


Call me jaded, but it’s rare now that I find a gardening book that makes me understand gardening in a new way.  But this week, just such a book crossed my path.  It’s Understanding Roots by Robert Kourik.  In it, Kourik shares the fruits of his own deep experience as a gardener as well as his research into a variety of obscure but fascinating studies of plant roots.

Particularly interesting are the portraits of root systems of tree, shrubs and herbaceous plants that were obtained by excavating and tracing roots down into the soil.  Just looking at these dispels a number of gardening myths.  For instance, the diagrams of a number of fruit tree root systems suggest that the traditional way of fertilizing such plants, with a circle of holes drilled under the outer edge of the tree canopies, miss most of the feeder roots that supply the trees with nutrients.  And if you think you are going to dig out a dandelion taproot and all, first you should look at Kourik’s diagram of a dandelion’s roots (see below)

dandelion001Kourik also includes astonishing material about  the mycorrhizal fungi that partner with plant roots, hugely extending their penetration of the soil and their ability to extract nutrients by as much as 1,000 times.  In addition to their beneficial effect on the individual plants, mycorrhizal fungi also link plant to plant, serving as a means of communication – if  a pathogen invades one plant, nearby plants may sense this through mycorrhizal connections and activate their defense systems.

Also included are practical chapters about  methods for transplanting trees that maximize root growth (I’ve also reproduced Kourik’s illustration of that), the effects of various kinds of mulch on tree roots, and the effect of gray water use on root growth (Kourik is a leading authority on gray water systems).

There are very few books that I, as a gardener, consider must-haves.  But Understanding Roots is a new entry on that short list.

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Thomas Christopher

My father was a compulsive tree planter, but it was my mother who taught me the finer points of gardening.

Her homeschooling was followed by two years in the New York Botanical Garden’s School of Professional Horticulture, and then ten years as horticulturist at an Olmsted Brothers designed estate on the Hudson River Palisades.

I’ve worked as a horticultural journalist for 35 years, contributing to publications ranging from Martha Stewart Living to the Journal of the Royal Horticultural Society and The New York Times.  My most recent book is Nature Into Art: The Gardens of Wave Hill, which is a tour of the lessons to be learned from that great public garden.  I’m currently focusing on my new podcast (at thomaschristophergardens.com) which features weekly interviews with leaders of environmentally-informed gardening.

My special enthusiasms include sustainable gardening, especially sustainable lawns;  heirloom chicken breeds; and recreating vintage New England hard ciders.


Contact Tom by email


  1. The mycorrhizal fungi communications link would explain the concentration of pests like Japanese beetles and aphids I observe every summer on very limited and widely spaced individuals in a large bed of hundreds of identical plants. I always assumed those were particularly tasty specimens, but now suspect that their neighbors have developed a way of dialing back their appeal upon getting the news of trouble in the neighborhood. Pretty fascinating.

  2. Sounds like a wonderful book. A few years ago I took an on-line Coursera course called “What a Plant Knows”, and it is pretty darn amazing what is being discovered about how a plant senses the world and communicates with others.

  3. This is a GREAT book. And it is done in a simpler form that allows anyone to get excited and understand this CRUCIAL component of healthy plants and soils. I have taken this info – not necessarily from the author – to tailor my composting operation and end products. It is exactly why I apply specific protocols to my batch processing; and also why I use this quality Fungal Dominated end product for green infrastructure and remediation projects. It WORKS and it Nature’s millenial experienced end product herself. Duh. In the end, so simply and so rudimentary…. it ultimately brings us back to LEAVES. We are soooo damn obsessed with “cleaning” leaves in the fall and in the spring. Why? But, I am now realizing that I am preaching to the choir here. We need to spread this science throughout the landscape architecture, design, construction, “maintenance”, etc… industries. And, we need to communicate this all to the homeowners that are the ones usually demanding a “clean up”. It is soooo ludicrous that we “clean up”. Foolish and reverse environmental.

  4. That dandelion picture is falsely daunting. I have dug out the thick portion of dandelion tap roots from my lawns for 30 years and it works. It enrages me when chemical companies use photos like this to imply that it is impossible to get rid of dandelions without their dangerous products. I had to speak up because your comment adds fuel to their fire. They generally do not survive when most of the thick root is dug out.

    The talk about leaves is also ignorant and damaging to gardens. Leaves benefit under trees and shrubs as long as you do not want bulbs or perennials to survive. As a gardener, I mow up leaves when using them as a mulch so that they do not mat and smother plants. All the sunny flower gardens do not need that poor advice. My neighbors trees spread leaves with disease over my garden. I do not compost hot enough to kill the bacteria. Most urban areas will supply the unwanted leaves of others to gardeners as thoroughly cooked compost– an excellent solution!

    • That illustration and my reproduction of it are by no means an endorsement of chemical herbicides. My experience has been different than yours: I have found that a single digging of the root is often insufficient to kill a dandelion plant. But I harvest the dandelion greens in spring as a spinach substitute. I have found that a couple of diggings plus depriving the plant of its foliage is usually enough to kill even a stubborn dandelion.
      Sounds like you are doing great things in your garden!

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