August 2006 General Meeting notes.

For our August meeting John Thompson spoke about how to use oaks for bonsai. Oaks are a common species for bonsai which can be quite rewarding; many types of them are well adapted to our climate. John brought examples of different styles and species which he has in his collection. Cork oaks are native to Europe, evergreen with gray green leaves and wonderfully deeply fissured bark, which is actually the source of wine corks. Coast live oaks, the most commonly used species in bonsai locally, are readily available for collection in our area and have smooth bark and leaves with a slight curl and spines on the edge. The English Oak (quercus suber), like the valley oak (quercus lobata), is a white oak and is deciduous; both species have larger and more lobed leaves than the evergreens; they also tend to have bark that is rough, splitting into small plates when the tree is older. There are many more species, however in John’s experience these four are the easiest to collect and grow. Blue oaks grow quite slowly as do most scrub oaks, although in both cases the leaves are smaller and possibly more attractive for bonsai if one has suffiecient skill and patience.

Oaks are entirely different beasts when it comes to styling. The typical model for bonsai, a pine tree, has branches that leave a single trunk and swing downward, where an oak has multiple trunks splitting from a massive trunk which are much like a water fountain. The branches are crooked and gnarly and after rising they head outward before, in many cases, starting to weep back downward. (see the article from the July Newsletter on oak styling for more information.)

John encouraged members to collect and start acorns, saying that it is quite easy and will reward you with a bonsai in less time than you might imagine. John says that the young trees don’t need to be fertilized for the first year because the acorns contain all the nutrients that are needed for fast growth. He wires the small seedlings after they get to be about 6 inches high, twisting the trunks and putting a little movement into them. The twist is the more important part since it introduces a slight spiral to the trunk of the tree which will increase the interest in the bark and the shape of the trunk later, giving it a “muscular look.” Oaks are not readily grown from cutting, although air layering is not difficult.

Collection of wild oaks is best accomplished between January and April, although if you have a chance, and the trees are being removed, it can be done with some success at any time of the year. Remove nearly all the foliage when you collect a tree, leaving a few leaves at the tips of branches. This will force the tree to bud out from the trunk and reduce the transpirational loss of water therby reducing the stress caused by a lack of roots. Collect as many roots as possible, even if you have to go deep into the soil, they can be removed later as the tree sends out new roots closer to where the nebari should be. Flat cutting, (removal of all roots and chamfering of the edge of the cut with a razor)even with the best aftercare including bottom heat and a misting system in a greenhouse, is a coin toss with oaks.

John addressed concerns about powdery mildew and other fungal diseases on oaks, especially in San Francisco where the weather is cooler and more damp, saying that a tablespoon of hydrogen peroxide to a quart of water sprayed occasionally on the leaves will control their spread. Oaks are subject to water molds, which typically attack weakened trees or roots which have died from summer heat and then started to rot during the winter rain. Root heat, although not a severe problem in SF, can be avoided by wrapping the pot in reflective bubble wrap (commonly found in heating/plumbing supply stores) and covering the soil surface with shade cloth. Make sure that trees are planted in coarse soil and tip large pots up slightly to avoid soggy conditions during prolonged winter rains.

Repotting of evergreen oaks can be done at any point when the tree is dormant. This happens during times of prolonged hot weather (uncommon in SF) and during the winter. If all the growth on the tree has hardened off (is not supple and new, but contains wood) then it is typically safe to repot. Major root work is still best left for spring, right before new growth begins. Deciduous oaks are best repotted in spring as well. Evergreen oaks can be defoliated in August/September either partially or by cutting 50-80% of each leaf to stimulate new growth. This procedure should only be done to healthy oaks and only when you want more, shorter branches. If you need the branches to elongate to fill out the crown it is not a good idea to use this technique since it slows the growth of the branches.

Oaks should be fertilized like almost any other tree, regularly; John uses any of the Whitney Farms oraganic mixes and applies the fertilizer by spreading it across the soil surface and working it into the top with a chopstick. Because the fertilizer breaks down, it will eventually form a crust on the soil, preventing water from entering properly. When, or before, this happens, rake off the top layer of soil and replace it with fresh soil. John cautioned against the use of Osmacote, a chemical-based time-release fertilizer which is temperature sensitive, because when it is too hot it can burn the trees.

Many thanks to John for an informative and useful program.

Tags: acorn, john thompson, oak