Field Report: Camelia Bloom Cycle

We've lived in our San Francisco Bay Area home for over 23 years, through all kinds of weather and environmental conditions. During most of that time, the camellia bushes (Camellia japonica spp.) have bloomed like clockwork from November through February. I've used them to decorate holiday tables from Thanksgiving to Christmas to Valentine's Day. 

Pink camellias

In the last several years, however, the camellia blossoms have appeared later and later in our yard, often from late January to April.

White camellia

Camellias are lovely whenever they arrive, but the change in bloom cycle does represent quite a shift. Admittedly, our bushes are aging and may be feeling their years. It will be interesting to see their bloom cycle trends in the years to come. I may need to find an alternative bloom for my winter holiday table settings.

Red camellia

 

Air Spade

Soil compaction results when soil particles are squeezed together, eliminating air space. This makes it harder for water and air to infiltrate the soil, and for roots to grow and take up water and minerals. While researching methods of restoring compacted soil in Soil Restoration Under the Oak, I came across an arborist tool called an air spade (also known as an air knife). 

The air spade is powered by an air compressor, and moves soil away from tree roots at super-sonic speed without damaging the roots. The video shows several tree care applications, including vertical mulching around marker 0:54, and soil aeration around marker 2:25. Note that this is not a product promotion, just a very informative video. You can find more examples by searching the Internet using a variation of "air knife for arborists".

In our case, our arborist did not recommend something as powerful as an air spade, since the compacted soil under the oak tree is not in a foot traffic area. The wood chips are sufficient to start.

Learn more:

• Keeping Native California Oaks Healthy, by Bruce W. Hagen, Forest Pest Specialist, Forest Pest Management Program. California Department of Forestry and Fire Protection, Tree Notes, Number 7, June 1990.
• What is a Super-Sonic Air Knife, by Conner of Root Cause Seattle (video).
• AirSpade for Arbor Applications

Plant Aquarium: Polypodium

Ferns make an appearance in our yard every winter. The seasonal rains stir them from dormancy to life. Tender leaves unfurl and capture the golden winter sun, providing beautiful pools of light under the trees. I bring a little of that light into the kitchen using my plant aquarium.

Polypodium californium

These ferns are in the Polypodiacea (or Polypodies) family. The name is derived from poly (many) and podion (little foot). Polypodies are terrestrial or epiphytic, with a creeping, densely hairy or scaly rhizome that bears fronds at intervals along its length. The leaf form is pinnatifid, with spores forming on the underside of the leaf. 

Polypodium under the oak tree

Spores developing on the leaf underside

The Polypodium californium can be found throughout our yard after the winter rains, especially under the juniper and oak trees. They do well in moist shade, as well as full winter sun, and go straight to work producing their spores. As the rains cease, the ferns dry up until the are completely dessicated. But the rhizomes are beneath the surface in the soil, ready to spring to life when the winter rains return.

Leaf and rhizome structure

Learn more:

• Wikipedia
• Jepson Herbarium
• U.S. Department of Agriculture
• U.S. Forest Service - article on ferns.

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