Thinking About Tropical Diversity (in the redwood forest!)

On my daily walk, the forest of redwoods (Sequoia sempervirens) the S. gigantea is pictured here), oaks, Douglas firs, and many understory plants seems rather diverse. I wondered if this diversity had any implications to gardens. Maybe yes, maybe no. But today, for some reason I'm thinking about the tropics as well as the temperate climates.

In my opinion, using tropical diversity as a model in the USA is childlike. While the tropics often have lots of vertically-integrated plants, the temperate American landscape, with its hardwood forests, meadows, and prairies, is less vertically complex.


The nutrient mass is primarily above the ground in the tropics, the soil is rather “thin”. By comparison, the deeper soil is the reservoir of nutrients in a temperate ecosystem. Some plants in the tropics actually fix nitrogen on their leaves – “Experiments in a Costa Rican rainforest revealed that fixed nitrogen [by blue-green algae] is directly transferred into the leaf “ (Many tropical plants and trees do fix nitrogen in the soil, but it is “recycled” much more quickly.) From MONGABAY.COM: “The colonial settlers did not realize that they were dealing with an entirely different ecosystem from their temperate forests where most of the nutrients exist in the soil. In the rainforest, most of the carbon and essential nutrients are locked up in the living vegetation, dead wood, and decaying leaves. As organic material decays, it is recycled so quickly that few nutrients ever reach the soil, leaving it nearly sterile”. While in the temperate climates, nitrogen-fixing bacteria grow only the roots beneath the soil’s surface—primarily Rhizobium spp. bacteria found on the roots of the bean family (Fabaceae or Leguminosae) gather the nutrients, especailly nitrogen.

The difference is considerable when applied to the practical. Gardeners in temperate climate work to enhance the fixation and storage of nitrogen the soil mass. While tropical gardeners can rely on foliar feeding of nitrogen and the rapid recycling of nitrogen in a thin soil. (Sugarcane production requires no additional nitrogen due to the independent fixation of this element.)


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Silly Nuts

While this has little to do with roots, except that the peanut comes from the soil. Peanuts are not harvested above ground.

On my way to-and-from St. Louis, MO; via Southwest airlines, I got this packet of dry-roasted nuts with the silly warning. (Click on the image to read the text on the packet.)

Duh. Some people can't seem to understand the obvious.

(I guess they're also not Kosher.)

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The Myth of the Range of Tree Roots

The following is text from my book: Roots Demystified, Change Your Garden Habits to Help Roots Thrive.

The best book on the topic of fruit tree roots is The Root System of Fruit Plants compiled by a Russian named V. A. Kolesnikov. (As with most scientific papers, only initials are used for all but the surname.) Kolesnikov’s scientific papers appeared from 1924 until 1968, indicating that the USSR regime certainly valued his distinctive research.

Kolesnikov’s primary modus operandi for studying roots was the one he called “The Skeleton Method.” As with Professor Weaver’s studies, this method entailed precise excavation of the roots. In imitation of archaeological techniques, shovels were used first, followed by scoops and, eventually, brushes. This approach preserved more fine root hairs during excavation than the most common practice of using water forced from a hose, or even more than simple washing of the roots.

Kolesnikov’s conclusion is that fruit tree roots grow one-and-one-half to two and even three times the width of the foliage above them. More amazingly, he states that this ratio is maintained throughout the life of the tree, regardless of the rootstock, species, and soil (my emphasis added). This is clearly seen in the apple tree illustration depicted in the left side above. (Click on the image to get a better view.) Each type of fruit tree maintains a slightly different ratio of root mass to canopy. The best place for water, fertilizer, compost, and mulch is beyond the foliar dripline (canopy). This applies to most trees, not just fruit trees. The roots of fruit trees are studied more than ornamental or native trees because they are economic crops.

The illustration on the right is the misguided imagination of a graphic artist. Pretty to look at, but dead wrong. The roots in no way mirror the above-ground foliage.

The relationship of the width of a tree’s root-mass to the amount of moisture it should receive is critical. Applying water near the trunk is wasteful in any climate. In a climate that routinely experiences short droughts of a month or so up to six months (as in parts of the Southwest), drip irrigation is the most efficient way to distribute water to an entire root system.

The climate, however, need not be arid for trees to benefit from drip irrigation. In a study of established pecan trees in humid Georgia, trees with added drip irrigation showed a 51% increase in yields.

It's nuts to irrigate any other way.

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Pop goes the weasel (tree)

As written in my book Roots Demystified, Change Your Gardening Habits to Help Roots Thrive, amendments are materials such as sand, peat moss, compost, and rice hulls have been added to the planting holes to supposedly improve drainage and keep the soil loose and friable. Fertilizers, such as blood meal, cottonseed meal, greensand, and wood ashes, are those ingredients added to provide mostly nutrients. Some amendments, such as compost, are thought to do both improve drainage and act as mild fertilizers.

One of the best studies of the effect of amendments for fertility was done at Oklahoma State University at Stillwater by Joseph Schulte and Carl Whitcomb. They planted 108 silver maple trees with 11 different soil treatments and a control (untreated planting hole). One conclusion was: "no benefit was derived from the use of soil amendments either with a good clay loam soil or a very poor silt loam subsoil." They found that the control plantings with no additional amendments generally outperformed the plantings with amendments for drainage and fertility.

The loose soil of the amendments in a traditional planting hole makes something like an underground swimming pool full of water when it rains hard, drowning important root hairs. Adding a lot of amendments only leaves the roots unprepared for the shock of what lies beyond the amended area. (And nobody can amend the area of the mature root system seeing as how much wider it is than the foliage.) Often the roots fail to make it out of the well-amended hole and merely circle around in the loose planting medium, rendering the trees likely to blow over during a storm. The trees most tolerant to wind are those with the widest root systems. Or, as the photo shows, not spreading the roots when planting can allow the tree to simply pop out of the ground when hit by a car or pulled out by hand.

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Doughnuts of Death, Mounds of Mulch

I just got back from the land of “toxic” mulch – the donuts (as spelled by Dunkin’ Donuts) of death in St. Louis, MO. Every landscape contractor (and maybe home gardeners mimicking the landscape companies) seems to be having a contest as to how high they can pile mulch around tree trunks. Some have mounded mulch 16 inches high or higher. These donuts of death are disasters in the making. Root rots (Phytophtora spp.) like a warm and moist/wet soil. Mulching tree trunks so high has all the ingredients needed for the rot of trunks to kill trees. I saw one tree that had mulch apparently piled over the graft of the now dead tree. (Unfortunately I didn’t have my camera with me at the time.) As the photo says, we must put a stop to this uninformed practice. Landscapers must abandon these donuts of death.

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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