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

"Natural" Gardens?

Their really is no such thing as a natural gardener-made landscape. All gardens are constructs made by people, not by nature. Our gardens ultimately serve our needs, our sense of aesthetics. This means every gardener is really servicing their own ego. Our gardens do look nice, but they don’t really look natural. A natural garden would look as if nobody planted it or tends it. Therefore, a truly natural landscape would not satisfy most gardener's egos. If nobody recognizes the yard as the product of another person, nobody gets any compliments. A purely natural landscape would look so naturalized that most people would just walk by without noticing. The ultimate goal of an ego-free landscape designer or gardener would be a garden which no one identifies as manmade. But I've never met such a gardener.

Our gardens will always be a constant dialogue about the following terms: natural-like, naturalized, earth-friendly, sustainable (the latest buzz word), or environmentally-sound. Unnatural doesn't mean malevolent. We can have reasonably natural-like gardens that meet every definition of beautiful. Such landscapes are nice and unnatural.

Given that we are growing artificial gardens, exactly how natural-like can we get? More environmentally responsive than we may think. But the answers are in the details. Here's some pointers:

Gardeners usually try to do too much. Some yards have plenty of natural landscape to begin with. The typical approach is to remove almost everything that's there, buy a bunch of topsoil and plants and put completely new stuff back. Far from natural. And costly.

Don't even think of planting until you've fully realized the potential of what nature already provided. All that's often required is to selectively thin, prune or remove. The idea is to sculpt your existing plants to reveal their hidden form and texture. It's like Michelangelo carving away bits of stone to reveal the magnificence of the David.

Carefully trim limbs from a tree to reveal a serpentine or wonderfully-textured trunk(s). Or, shape existing native shrubs to reflect the line of a nearby tree or a distant hillock. Pull out weedy exotic shrubs to display the curve of a tree trunk, the rugged shape of an immense boulder or the multiple trunks of a large shapely shrub. Weed out exotic grasses to leave behind a scattered pattern of native grasses.

Or, as photographed here, carefully open up an odd-shaped hole in a tree's canopy to provide a slice of the distant horizon, a nearby lake or the silvery ocean. This is a garden in Big Sur, CA that is simply composed of trimming the upper limbs of a native coast oak (Quercus agrifolia) and a planted, but carefully placed Ceanothus spp. (known as tick brush or wild lilac, NO relation to the popular common lilac – Syringa vulgaris). This section of the garden is the closest to a constructed, native landscape I’ve seen.

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

Taproot Myths Revealed

This is a photograph of a young tan-oak seedling, sometimes called tanbark trees as their bark was stripped off and used to tan animal hides. These trees used to be classified as a species of Quercus (oak), now reclassified by botanists with time on their hands as Lithocarpus densiflorus. Don’t ask me why. This seedling has a stem with a few leaves five inches above ground and seven inches of a taproot, all I could dig out. (Click on the photo to see a much larger image.)

In my book, Roots Demystified, change your gardening habits to help roots thrive, I talk about how few trees actually grow with taproots. Oaks are an exception, for awhile.

Some Californian and western oak trees (including the tanbark oak), begin growing with a taproot, which then naturally atrophies. The loss of the taproot can begin as early as the first or second season. When the young seedling of a blue oak is a mere three inches high the taproot can already extend 40 inches into the soil. After a number of years, the taproot withers, to be replaced by heart roots (which angle down from the base of the tree) and many laterals, with vertical sinker roots. In Spruce (Picea spp.), Hemlock (Tsuga spp.) and Cedar (Cedrus spp.) trees, at less than eight years, the lateral and oblique roots take over the role of support and the taproot declines. (From: “Natural Root Forms of Western Conifers”, S. Eis; From: Proceedings of the Root Form of Planted Trees Symposium, page 24, 1978.) After the taproot atrophies, the new root system grows more horizontal and oblique roots and resembles a fibrous root system.

In my photograph the roots are about as long as the stem and leaves. However, much of the tiny taproot was left in the ground judging by the thickness of the bottom of this seedling as it was dug with a spading fork. The seedling sprouted in deep shade which probably accounts for the extended length of the stem.

Any oak planted from any container or balled-and-burlapped stock has effectively had its taproot destroyed and forms a fibrous (heart roots) root system.

I think the sturdiest oaks are grown like nature, from seed placed where you want a specimen for your grandchildren to climb on.


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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

This Tree Needs Caterpillars

Caterpillars are pests aren't they? Not always.

It turns out the native coast live oak (Quercas agrifolia) that grows around my house co-evolved with a tiny caterpillar, appropriately named the oak-leaf caterpillar. Without the caterpillar, the oak tree might die during years of stress.

A nursery in Los Altos, CA has a gorgeous coastal live oak about 75 feet in diameter. During the drought of the early ‘70s a lot of trees were very stressed. A neighbor near the nursery sprayed their oak, “to get rid of the messy droppings and fallen leaves”. The nursery carefully watched their tree lose many leaves and be riddled with leaves partially eaten by the oak-leaf caterpillar.

Guess which tree died?

The neighbor’s. Because it had 100% of it’s green leaves to transpire moisture. Even an organic spray, such as Bacillus thuringiensis var. kurstaki, would have lead the tree to an early death. At the nursery, the tree survived as much of it’s leaf area was consumed by the caterpillar, offering less area for transpiration.

Judging by the moths at my screened windows and the partially-eaten leaves, the first round of oak-leaf caterpillars is here. There are two to three groups of moths each season depending on how dry the year is.

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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

Living With the Roots of an Oak Tree

I laugh (and cry) at the little orange fences they put around oaks during construction. They are nearly worthless. While it keeps vehicles for hitting and scaring the bark, it in no way protects the feeding roots.




As a maintenance gardener I’ve had to dig up a few oaks. And just below the ground the roots have a covering much like bark. Bark absorbs very few nutrients. In a study of 25-year-old apple tree in the UK found that the first four feet from the trunk accounted for less than 10% of all the water and nutrients absorbed.

The wobbly-orange fences are, at best placed at the edge of the foliage. A good start as it may help to keep water off the trunk’s base. But this is a far cry from protecting the majority of the root system’s feeding roots.

In the photograph to the left, the construction company dutifully surrounded the oak’s dripline. But all the machinery and the house itself cover what used to be the leaf litter, duff, and organic mater (humus) that once both fed and protected the young feeding roots.

The tiny root hairs, that live for just a day or so, tend to grow up into the fertile strata of the humus and duff zone. They, like all plants, want to be the first to capture liberated nutrients as they become avaiable. As one researcher put it—“roots grow up not down”. While a bit overstated, they fact is the youngest rootlets and their root hairs reside well beyond the canopy of the tree, where all the construction is taking place. (Learn more in my book Roots Demystified,)

(See my Blog of March 31st to see diagrams of the extent of a roots wanderings.)

At one-half to thee times, or more of the width of the dripline roots gather nutrients and moisture far from the trunk or even the canopy.

The photo (on the above right) of the chairs face south along the Big Sur coastline are a good attempt to protect to crown of the young California live oak from moisture in the summer. The gravel does allow rain in the winter to percolate down along with oxygen and harmful gases escape. The compacted gravel is a bit hard on the feeding roots, but the tree seemed health. Perhaps this is one solution to living among oak woodlands.

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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

A SOD Story, attachment to "my" forest.

Not the loss of lawns, which I can easily get over. But Sudden Oak Death syndrome (SOD).

SOD is decimating “my” forest. This alien disease first appeared in Marin county—the county just south of me—in 1995, although some say it may have been here since the mid ‘80s. It is caused by the water mold disease called Phytophthora ramorum.

The devastation of the tan oak along this ridge is enormous. As I drive home, the last three miles of the forest reveal hundreds of small and large dead and dying trees—some as high as 30 feet. It looks like a botanical firebombing. The dead trees stand out because they don’t loose their dead leaves for years, if not a decade or more. These sentinels are possibly a harbinger of things to come. SOD is decimating “my” forest. 

(A list of potential native host plants is at the end of this blog.)

Already the California bay laurel on this property is looking pretty shaggy and there is die-back on some of the limbs. Tan oaks and California bay tress make up 80% of the trees surrounding my house. Some say “this may merely be one of nature’s ‘house cleanings,’ removing genetically weak or damaged trees and leaving the healthier, stronger ones to produce better, sturdier offspring.” Well, I’m looking at a dead 40-foot high by 50 wide dead tan oak tree just 40 feet from my office and it’s not a pretty picture. I keep telling myself it wouldn’t be so bad if the leaves would fall off so the tree doesn’t look so miserable. But I still resent the death of these trees. These trees may follow the way of the elms that once graced so many yards and streets and the chestnuts that once were the major forest tree in the Eastern woodlands. But I hate it when it’s happening in my forest.

There will be a cascading effect on plants and animals as these trees die in greater numbers. As an example, the acorn woodpecker makes good use of the nuts from this tree. Squirrels nest in it. More than 300 species of animals; including 170 species of birds, 80 or more mammals and 60 varieties of amphibians and reptiles, and more than 5,000 insects make a home out of the habitats provided by the coastal live oak and tan oak trees, according to Bill Tietje, a natural resources specialist with the University of California Cooperative Extension. An acre of oak woodlands can have 10 to 100 million individual invertebrates which help to digest the decomposing oak parts to recycle nutrients for new growth. In the words of John Muir, “When we try to pick out anything by itself, we find it hitched to everything else in the universe.”

The death of tan oaks has been a great struggle at learning how to be unattached to the flow of nature (and mankind for that matter.) Sometimes as I drive home I simply gaze in a way that seems to selectively block out the view of the brown-leaved ghosts of the oak. I use to return from a trip out of state or the country and wonder in amazement at why I went somewhere else when it’s so beautiful here. Now when I return, I’m shocked at the death in the forest that I’ve forgotten about when I traveled. The forest may not cry, but I do. 

The ecological changes that happen will be slow and I probably won’t see the recovery or replacement of this wonderful tree in my lifetime. So the tragedy seems so personal. I am only one piece of the ecology but a very selfish one that doesn’t want to witness the slow demise or partial downfall of this tree that was here long before me. I just can’t let go.


This is the list of those trees and plants known to be host plants for the disease in California.

Scientific Name Common Name(s)
N= Native, MH = Grows around my house.

Acer macrophyllum Bigleaf maple - N
Adiantum aleuticum Western maidenhair fern - N
Adiantum jordanii California maidenhair fern - N
Aesculus californica California buckeye - N, MH
Arbutus menziesii Madrone - N, MH
Arctostaphylos manzanita Manzanita - N. MH
Rhamnus californica California coffeeberry - N
Heteromeles arbutifolia Toyon - N
Lithocarpus densiflorus Tanoak – N, MH
Lonicera hispidula California honeysuckle – N, MH
Pseudotsuga menziesii var.
menziesii & all nursery
grown P. menziesii Douglas fir - N, MH
Quercus agrifolia Coast live oak - N, MH
Quercus chrysolepis Canyon live oak - N
Quercus kelloggii California black oak - N
Quercus parvula var. shrevei
& all nursery grown Q. parvula Shreve’s oak - N
Sequoia sempervirens Coast redwood - N, MH
Trientalis latifolia Western starflower - N
Umbellularia californica CA bay laurel, Oregon myrtle – N, MH
Vaccinium ovatum Evergreen huckleberry - N, MH


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

Note: I somehow lost the usual section "Post a comment". To leave a comment, simply click on the area/button that says "___ Comments". Clicking on the title of a Post under "Blog Archive" also gets you to a view that gives the option of leaving a comment. I hope to figure this out soon. Robert

Visit my web site to learn about my gardening books.