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Master Gardener: The Importance of Roots

by Joan Bergsund

Roots? I´m not talking about your family tree, but of the root structure of your plants. We´re inclined to think “out of sight – out of mind” but we need to pay much closer attention to those roots which support and nourish the plants above them.

Robert Kourik of Occidental has published several books on gardening subjects. His latest, “Roots Demystified: change your gardening habits to help roots thrive” should be required reading for all gardeners. He tells of his early interest in landscaping and his discovery that illustrations of some trees showed the root structure as a reflection of the canopy. Think of mirror images. He discovered that the area occupied by tree roots can be five times greater than that of the foliage above ground. His book covers the root structures of lawns, shrubs, vegetables, fruit trees, native and ornamental trees.

Just to catch your attention I´ll quote some of the interesting facts – not myths – that he learned from his research:

Some roots pass water on to the nearby roots of other plants.

At the end of its first year´s growth, an apple tree can produce as many as 17,000,000 root hairs with a total length of over a mile.

While feeding near the surface, some shrubs, like Artemisia tridentata, have roots as deep as 30 feet.

About 90% of a tree´s roots are in the top 18 inches of the earth around it.

A cucumber seed can grow a taproot about three feet deep.

So, what do these interesting facts mean to us? By paying attention to the root structure, we can learn which cultivation and nurturing methods work best in our own gardens. Having endured another summer of three-digit temperatures, we can prepare for maximum garden health and productivity by being certain our roots are properly cared for. We should protect those roots, nurture the soil, fertilize cautiously, and use water and mulch wisely. This advice doesn´t sound like anything new.

But listen: The area left bare around the base of a tree should be way beyond the drip line. This is where irrigation and fertilizing, if any, should occur. A tree planted in a lawn should have a 20´ doughnut of bare ground surrounding it.

Most of Kourik´s inspiration and information comes from his discovery of John Earnest Weaver (1884 – 1966), Professor of Plant Ecology at the University of Nebraska for 47 years. Living on the great American Prairie stimulated his interest in plant ecology. He used an archeologist´s approach and literally spent hours, if not years, in the trenches to excavate root zones of plants. His copious notes and exquisitely drawn illustrations lay buried in the agricultural library at the University of California, Berkeley, until they were discovered by Kourik in the early l980s.

One of Weaver´s particular interests was buffalo grass (Buchloe dactyloides), a native of prairie grass habitat. Buffalo grass roots can penetrate the soil to a depth of seven feet to utilize deep moisture, although nutrients, if available, will be absorbed in the top 12 to 18 inches. It can go 21-45 days without irrigation. Two varieties of this grass are now growing at the Master Gardener´s Demonstration Garden at Cassina High for use in our foothill environment. Visit the garden on the first Saturday of each month to see this grass in action. It may be right for your garden.

Information on shrubs-as well as grasses, forbs, native shrubs and trees-was gleaned from studies done for the Los Alamos National Laboratory in New Mexico. Titled “Rooting Depths of Plants on Low-Level Waste Disposal Sites” (1984), the interest was in plants which would adapt to extremely dry habitats, requiring little or no monitoring or maintenance of the disposal sites after 100 years. As examples, plants whose roots are illustrated include penstemon, buckwheat, alfalfa, mountain mahogany, Ponderosa pine, Pinon pine and one-seeded juniper.

A long chapter on vegetables covers most of the veggies we grow. Limited space forces me to report on only two. A single asparagus plant, six years old, can have roots almost eight feet wide and eleven feet deep. The illustration is from Weaver´s work published in l927. And everyone´s favorite, the tomato, transplanted as a seedling, can grow roots up to five feet wide and nearly as deep.

Kourik suggests using hay bale culture for growing potatoes. Functioning like a raised bed to protect roots from gopher attacks, hay bales can be amended, soaked and planted with potatoes. After harvest, the hay bales can be replanted with more potatoes or a different crop. As the bales eventually deteriorate, you´re left with a rich soil amendment/mulch which can be distributed throughout the garden.

The author also promotes the newspaper method of smothering weeds in preparation for planting. Master gardener Marlys Bell wrote an article on this system, which she uses extensively in her own garden. See http://cetuolumne.ucdavis.edu .

The appendices offer information on drip irrigation, legumes to improve the soil, searches for tube-grown plants and useful lists of shrubs and trees. Most intriguing are the practical tips for gardeners seeded throughout the book. We talk frequently about sustainability; with improved techniques in caring for our roots, our plants will be healthier and last longer.

Joan Bergsund, master gardener, goes underground to study her roots. She recommends this book for gardeners who thrive on detail and are planting for the long haul.