Soil Restoration Under the Oak

 The soil under the oak tree needs some help. The soil has compacted over time, and some of its roots are exposed above ground. The root zone is not a foot traffic area, but over time, gravity and natural drainage have eroded and compressed the soil. We stopped irrigating the area years ago. The lawn died, and was replaced with moss (beautiful during the rainy winter season, but less so during the dry summer months). It's good that we stopped watering, since too much water during the warm season invites disease for oaks.

Majestic oak tree trunk and limb

I scheduled a consultation with our arborist from Brende and Lamb to discuss the health of our oak tree, and get the scoop about soil restoration. Our landscaper had expressed concerns about several small cavities and cracks in the bark at the base of the tree. We've been letting the oak leaves collect under the tree in a natural duff to jump start the soil restoration process. I wondered whether we could do more, such as bring in a load of wood chip mulch (see Wood Chips Everywhere!), or aerate the soil using a soil aerator or an air spade (a.k.a, an air knife). I also wanted to discuss irrigation, since we have plans to modernize our old, broken system.

Small cavities in the oak bark go back several inches

Our arborist has been monitoring and pruning our oak for years. He opined that the cracks in the bark were part of the natural growth pattern, and that the small cavities were probably fine since they did not harbor standing water. Limb attachments in a v-shape are more worrying, since they can trap moisture that can lead to rot (versus u-shaped attachments, where water rolls off more easily). He recommended that we bring in wood chip mulch to protect the soil, and encourage its restoration. He also recommended that under our big trees, a soaker hose  is a good irrigation solution (even oaks appreciate an occasional (monthly) drink of water during the hottest months).

Ridges and roots under the oak tree

Optionally we could aerate the soil. He thought the air spade would be overkill, since our oak is not in a high traffic area. But he described a method of using a deep-root irrigator to create holes in the soil, and then filling them with organic mulch to enable the exchange of oxygen in the soil. Many tree services offer the service, but it would be quite expensive for the area under our oak. Instead he recommended doing it ourselves - chipping away at it over time, especially during the rainy season when the soil is typically moist. It's a pleasure to meet with someone who knows and loves trees. We now have the information we need for the next steps!

Wood chips in the foreground, and leaf duff beyond

The Chinese Elm Drops a Branch

Our Chinese Elm (Ulmus parvifolia) recently dropped a branch after several days of intense rain. The tree has Anthracnose, a slow moving fungal disease that eats away at the bark and causes cankers. Eventually a branch may become weak and die.

Branch descended from the Chinese Elm (Spring 2019)

The tree dropped another branch about two years ago, in similar circumstances, after the heavy rains that brought us out of the drought. What's unique about the tree is that, in both cases, the limbs descended slowly, making muted snapping sounds as the compromised wood fibers gave way. The branches did not come crashing down as they might have in other trees.

Another branch blocked gate (Spring 2017)

Our arborist has been monitoring the disease over the last 20 years, trying to keep the tree for as long as possible. It has lovely mottled bark, shiny single-toothed leaves, a graceful stance, and provides lovely dappled shade along side our big oak tree. So far we have been able to save the tree. As always, we called Brende and Lambe to clear away the fallen branch, aesthetically prune what remains, and assess the safety of the tree.

The branch has been removed and the tree still provides shade (Spring 2019)

Working With an Arborist

Arborists specialize in arboriculture–the care of trees, shrubs and woody plant material outside of a forest setting. They may work in a municipal or utility setting, keeping public trees healthy and safe, or utility right-of-ways cleared. They may work in a commercial setting, caring for private trees, removing dead or problematic trees, or providing consultation services. Certified arborists are well trained in the health and care of trees, and versed in the municipal requirements for urban trees.

The International Society of Arboriculture (ISA, http://www.isa-arbor.com/) is a great resource for finding a certified arborist, learning more about arboriculture, and finding out about certification. Becoming a certified arborist requires several years of field experience, rigorous testing, and ongoing education. The ISA provides certification in these key areas:

· ISA Certified Arborist

· Arborist/Utility Specialist

· Arborist/Municipal Specialist

· Tree Worker/Climber Specialist

· Tree Worker/Aerial Lift Specialist

· Master Arborist

An arborist is a wonderful asset for your urban garden. I’ve used Brende and Lamb in the San Francisco Bay Area for years, to prune and care for our big oak and elm trees. If we had contacted them at the first sign of trouble, we might have been able to save the maples.

Street trees in Dublin, California

Evil Comes to Eden

Death has come to my little piece of Eden - three Japanese maple have died. All three maples stand in a row, near a retaining wall, which separates the slope of the yard from the patio. All three maples have thrived since we moved into our home fourteen years ago. All three maples now show the same symptoms – first the buds did not develop last spring, then mushrooms and conks began to grow in the fall, then the bark peeled on the northern face of the trunks in the winter. Looking back, death happened over a period of time, so I could have take action sooner.

One of the maple trees - notice the
peeling bark

And, looking back, I can see several events that may have contributed – several years of drought, followed by two very rainy seasons. There was as sprinkler incident last spring, where we realized we had an underground leak, which might have flooded the root zone. Perhaps the soil itself is infected with something. A beetle infestation might explain the peeling bark (although, in the Arboriculture class I took last fall, we learned that pest infestations may be a secondary symptom for a tree that is already in a weakened state).

Symptom: dead branches

Symptom: peeling bark

Symptom: conk (the fruit of a wood-rotting fungus)

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Another possibility is that circling roots may have strangled the trees (I also learned in the Arboriculture class that many container grown trees develop circling roots; after they are planted, the trees grow fine until they reach a certain size, and then the roots cut off the vascular system and strangle the tree). And a final thought is that every living thing has a life span, and eventually dies. Enough speculation, it is time to call in our arborist, Brende and Lamb of Berkeley (http://www.brendelamb.com/), to diagnose the problem. They have been pruning my big trees and providing guidance for years.