Demonstration by John “JT” Thompson – Cork Bark Oak

Demonstration tree – collected native cork bark oak

On May 28, 2019, John “JT” Thompson performed a demonstration on a cork bark oak (Quercus suber).

There are some 20 native oaks in California. John is experienced in collecting many different types of native oaks. He brought in several species as examples of oak bonsai. He described the general form of native oaks as growing up and outward from the trunk and primary branches.

John discussed oaks’ adapting to their environment. Whether growing in wide open space to hanging by its roots on a hillside. This adaptation makes for ideal bonsai in numerous styles.

First, John examined the base of the trunk and surface roots or nebari. Cork bark was present on the lower trunk. He then evaluated a potential front view, sides and back. The trunk was tapered nicely and movement was present throughout the tree.

John talked about three styling or development methods – cutting back, defoliation and thinning.

Cutting back branches to two leaves and let them grow outward. Wire the first four to five inches and bend in an inclining slope, mostly up and outward, up and outward, then a little side to side movement in the same section. Allow the shoot tips to grow unrestricted for the remainder of the year, but remember to remove the wire when it starts to bite in, usually six to eight weeks later. John said cut back to leaves where you want new shoots to appear.

Defoliate healthy trees only. Defoliation should be done in early May to mid-June. After that is risky to the health of the tree.

Thinning out allows sun light to enter the interior of the tree. Here you are only doing a partial defoliation.

John spent some time talking about working with the younger branches or new shoots on oaks. New shoots can be wired after the leaves have hardened off. Meaning less succulent and stiffer leaf growth. Straight branches need to be wired for creating movement. The most important part of the wired branch is the three to five inches in the first year’s growth. The movement should be up and outward, up and outward, and then side by side, forming curves or arches. Then, let the branch grow out. The next year cut back leaving the bent in the branch. Let new shoots grow out. Select three new shoots, a front, side and back, and allow these to grow and hardened. The steps are repeated to develop ramification in the branches and eventually twigs.

There are growth periods to watch for. Cut back should be done in January. While working with new growth occurs in mid-February to March after the leaves have hardened off.

Cut back longer branches to have a more compact bonsai. Cut back to where you want division. Remove downward growing branches and weak branches. Remove dead branches and twigs from the tree.

John prescribed fertilizers once the tree has hardened off after the early spring growth.

He preferred using aluminum wire over copper wire for wiring branches. John believed copper wire would damage too many latent buds. Whereas aluminum wire was easier to work with on oaks. He said to watch out for the wire cutting or biting into the bark and advised removing the wire after about six to eight weeks.

Repotting – January is the prime time for repotting oaks. Collecting oaks was best done in the spring or fall after a rain. John preferred a deep pot over a shallow pot for oaks. Besides a usual bonsai soil mix, he uses about 12% horticulture charcoal when repotting. He also uses an organic supplement for root growth and development. Dr. Earth has a line of organic supplement products and fertilizer.

Watering – summer watering can bring on fungal issues. It is best to water in the morning versus evening. The soil should be watered, not the foliage.