Healthy Roots

As mentioned in my book Roots Demystified, Change Your Gardening Habits to Help Roots Thrive, if led by available moisture and nutrition, a tree may tunnel its roots through soil space ranging from an area one-half wider than the dripline to as much as three times further. A deep sandy soil offers little resistance to growing roots and allows for root exploration of three or more times the width of the tree.

This oak tree has mulch out to the dripline of the tree. While not the ideal it sure is a great improvement over how most developers treat native trees. This is the best example I have seen. It is located at a public community center. The sign offers great educational advice.

Unlike the dying tree in the previous blog (3-24-10), this oak trees is thriving.

“BUY FROM THE SOURCE TO HELP KEEP WRITERS WRITING”


Let me know what you think.Visit my web site to learn about my new book on drip irrigation and other gardening books.NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert

Real Apple Roots

The line drawing on the left is from a book in 1978 that got me confused, curious, and started my research on how roots really grow. The drawing on the right shows how far roots travel from their trunk & beyond the dripline (canopy). The red circles are the driplines. (Based on my book: Roots Demystified, Change Your Gardening Habits to Help Roots Thrive.) The roots pictured here are of an apple tree. Look how the roots avoid the compacted soil and even the roots of another apple tree.

Let me know what you think.

Visit my web site to learn about my new book on drip irrigation and other gardening books.

NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert

Even the pros mess up sometimes.

Planted deep as a coffin. Not really, but very deep. I just got back from a trip to St. Louis. The Missouri Botanic Garden is one of the of the top five public gardens in the country. Yet, the pros don’t always get it right all the time. It appears this poor tree was planted two feet lower than it should have been. (To be fair, it probably was the work of a well-meaning volunteer.) That’s my Dad showing how the tree desperately tried to develop roots closer to the surface. (Clicking on the image presents a lager image.) Too much energy to get feeding roots out near the surface and the death of the deeper roots led to the demise of this tree. Lesson for the gardener? Never plant a plant any deeper than it was grown in a pot or at the of color on the trunk of a bare root tree.

Plants Really Drink and Eat Near Our Toes.

I consider those ever-popular metal tree root deep-feeders as virtually useless and mostly harmful.

Spring has been warmer than past years up here “on the mountain”. Friends are thinking about watering. I hope they think carefully. (My plants and trees receive no summer irrigation. But that’s another blog altogether.)

The roots of many plants, it turns out, don't really get most of their water and nutrients from the deep regions of the soil. Rather, most plants, tree and shrubs gather all the moisture and nutrients they require from the top 12- to 36-inches, depending on the plant. The first foot is the most critical. Here is where the soils are most aerobic and this facilitates the exchange of nutrients from the minerals into soluble form that plants can absorb. Feeding root hairs actually grow up toward those first moisture-laden nutrients. (The lettuces pictured here can send roots as deep as four feet--if you don't have gophers! This is why boxes with wire bottoms should be 24-inches high instead of 12 inches. To give the roots "room to move". Yet the lettuces still get much of their "food" from the top 12 inches. So careful irrigation is a must.)

The roots of many plants, it turns out, don't really get most of their water and nutrients from the deep regions of the soil. Rather, most tree and shrubs gather all the moisture and nutrients they require from the top 12- to 36-inches, depending on the plant. The first foot is the most critical. Here is where the soils are most aerobic and this facilitates the exchange of nutrients from the minerals into soluble form that plants can absorb. Feeding root hairs actually grow up toward those first moisture-laden nutrients. (I describe this in more detail in my newest book - Roots Demystified, Change Your Gardening Habits to Help  Roots Thrive.)

An old adage advises gardeners to water trees deeply; this often means infrequent, but lengthy irrigation. Increasingly, drip irrigation has been used as a tool for deep, occasional irrigation. Infrequent, deep irrigation tend to produce two points in the total irrigation cycle where the soil life and root hairs are damaged enough to reduce plant growth—during both the drying stage and when the soil is too wet. Dry soil kills off the tender root hairs as they can’t survive too much air. When the ground is flooded, root hairs die and noxious gases can’t escape nor pure air enter—or as pure as it may or may not be.

The metal probe of a typical deep root feeder is 18- to 24-inches long. This means that the application of the water begins below almost the entire zone of maximum water and nutrient uptake.

Good pore space makes for healthier plants. An ideal mineral/humus/pore structure balance results in a crumbly soil that allows water to percolate down, harmful gases to vent out, and refreshing air to permeate the soil. Soil breathes 24/7 at a lumbering, beneficial rate we cannot see. A soil with a healthy structure allows for easy and deep root growth and will produce the best-looking lawn, garden and tree growth.

Root feeders flood the pore space of the deeper soils, which quickly becomes flooded and anaerobic. Sometimes the deep soil saturates and the irrigation water backs up toward the surface so that more shallow soils actually get waterlogged. It's a bit backwards to send the water through a 24-inch deep probe just to apply the water 6- to 12-inches deep!

I recommend you just toss your root feeder—actually, recycle the scrap metal parts. (China could use them.) A good sprinkler can do a better job. And a drip irrigation system will promote the best growth possible—better than any other method of watering.

One garden’s “deep” soil is another garden’s “shallow” soil. Another hidden assumption about tree roots concerns the depth of your garden's soil. There are places where glacially-deposited topsoil extends for dozens of feet, but these are more the exception than the rule. If you have such a deep, loamy soil, then rejoice, but remember that the majority of moisture and nutrient absorption by trees still happens in the top two feet of the soil. Typically, most suburban yards have a very shallow layer of topsoil, if there's any left at all after construction. If, for example, there is a continuous layer of rich-orange clay some 12 inches under the ground, then the 12-inch layer of topsoil is, for all practical purposes, the only place your plant’s roots will be feeding.


Most heavy clays, whatever the color—and dark blue or pale white-gray are the worst—are relatively worthless to feeding tree roots. While clayey soil has plenty of nutrients, their availability is locked up in its tight, anaerobic structure and strong chemical bonds. Tree roots can, over many years and decades, grow somewhat into clay soils, but the number and extent of roots in the looser topsoil in far greater and more important to tree nutrition.

Please post a comment - I want to know what you think.


All rights reserved, Copyright 2008

Visit my web site to learn about my gardening books.

NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert

Shameless Self Promotion

Roots ain't sexy. But plants need them to be healthy.

Thus I wrote a book about how roots really grow and ways a gardeners can have a better garden via healthy roots - Roots Demystified, Change Your Gardening Habits to Help Roots Thrive.

Check out my web site for more information (sample pages) and how to order: www.robertkourik.com

The book has been listed in Publisher's Weekly. They receive 1500 books per month and only list 450.

The best news came from the Midwest Book Review (one of the top 4 book reviewers for librarians):

“Superbly written and thoroughly 'user friendly', ‘Roots Demystified’ is profusely enhanced with twenty-five illustrative graphics showcasing extraordinary illustrations of excavated root systems in their entirety. A compendium of practical, comprehensive, and exceptionally well organized information, advice, tips, and observations that will benefit novice gardeners and seasoned professionals alike, ‘Roots Demystified’ is an excellent and strongly recommended addition to personal, professional, academic, and community library Gardening/Agriculture/Horticulture reference collections and supplemental reading lists.”

Here's my speaking schedule for now. 

March 30th. - On the radio on Michelle Anna Jordan's show "Mouthful" along with the extraordinary gardener Kate Frey of Fetzer Garden fame (who has also won prizes at the Chelsea Garden Flower Show in the UK.) 7-8PM on KRCB 91.1, in Santa Rosa CA 90.9 both on the FM dial.

April 5th - Book signing at Copperfield's Books in downtown Sebastopol. 11AM to noon.

April 15th (after paying your taxes - it's free!) - Oakmont, the Berger Center. 10-11AM (email me for directions - rkourik@sonic.net)

May 3rd - Lecture at Harmony Farm & Garden Supply, Graton, CA 10-noon.

May 18th - Book signing at Sonoma Mission Gardens 1851 Craig Ave., Sonoma, CA 4-6PM. 

I hope to meet you at one of these events.