Potentilla Exposed Root.

Worldwide there are about 500 species of potentillas, members of the Rosaceae (Rose) family. The specie growing in North America, northern Europe and western Asia is potentilla fruticosa, more commonly known as potentilla or shrubby cinquefoil. It is not a tree but a deciduous shrub with exfoliating brown bark, dusty green foliage, yellow flowers from June to October and often has bands of deadwood.

I collected this small shrub in September 1998. The tree was sandwiched between two pieces of rock that I pried open. What had initially caught my attention was the thick trunk emerging from the rock. Often you see potentillas that are quite small with narrow trunk diameters. Opening up this rock sandwich exposed developed roots.

At home, I potted the tree in a small training box and then waited for it to re-emerge after winter. At first I thought the tree might be dead because it took some time before it finally came out of dormancy.




June 1999 in training box.
First Design Attempt
During the summer of 1999 I let the tree recuperate and then in October I pruned and wired it. I had in mind a semi-cascade tree with the large lower right branch as the falling branch.

However, this was the beginning of an important design flaw. I had not really considered the exposed root form because I had read that this particular form was not as as it had been in the past. Additionally, I do not recall seeing any exposed root forms that I liked. Most of those I had seen seemed to be a mess of squiggly roots with a tree on top. They did not lookfavoured consistent or artistically appealing. But my biggest problem was being bound by convention which narrowed my design options.

In the spring of 2000, I tried to pot the tree in a cascade container but because of the long roots, I settled for a deep cascade pot with the hope that roots would develop higher up the tree.

In the spring of 2001, I continued to follow my semi-cascade plan with determination. The tree had failed to grow new roots higher up the tree while growing in the deep container so I repotted it in a shallow container. This time I wrapped the roots in sphagnum moss after I had applied rooting hormone, still hoping to develop roots higher up the tree. Then I could get it into the "perfect" semi-cascade pot I had.

In order to get the tree into this shallow pot, I pruned about one third of the small feeder roots. The tree continued to put out lots of foliage just as it did the year before (2000).
Flower Development
The flowers on potentilla appear later in the summer on the tips of the current year's new growth. When designing a potentilla, a decision has to be made that will influence the appearance of the tree: either incorporate long foliage extensions in your design or trim them off and lose the flowers. I have not come up with an answer to this paradox. Jerry Vlcek suggested that minimal fertilizing and less water will get both tight growth and flowers.

John Biel recommends developing the tree into a bonsai first, and then cultivating flowers. Further, when flower buds do develop, John suggests removing some of the flower buds before they open because the flower clusters are heavy and will make the small branches droop. Removing the dead heads promptly is also advised to avoid a "ragged" look

For my small shohin tree, I have chosen to cut back new growth but in the future will try to encourage flower buds using the methods mentioned above. For larger potentilla bonsai, where longer branches fit the design, flowers are a more practical proposition. 
 
Re-Design
In the spring of 2002, again without many new roots higher up the tree, I finally did what the tree was trying to tell me to do all along. I chose to use the exposed root form that Mother Nature had spent all that time developing. Many bonsai professionals have long advocated listening to your trees.

As before, I cut as many roots as I dared, about half of the feeder roots this time, and then repotted the tree in a small blue Japanese container. The result was very small foliage throughout the tree. During the summer, another set of leaves emerged that were larger. These were pruned out to keep the foliage size small and consistent throughout the tree. Less fertilizer would have also helped. The large amount of exposed roots appeared to be a bit heavy in comparison to the delicate foliage above. So I began to remove bits of exfoliating bark from the exposed roots creating less mass and more air spaces. In this regard more work has to be done to reduce the exposed root mass. Next spring I may remove or reduce a root or two.
After having the advantage of studying the tree's photo, I think the trunk should be tipped slightly to the right as it is growing up straight. Since the branches move to the right, so should the trunk line. Another task to do is to reduce the diameter of the falling first branch which is too thick compared to the main trunk. 

An interesting characteristic of potentillas is that the shrubs' roots feed growth veins that are quite distinctive. These veins can sometimes be readily removed which can be advantageous for design purposes. As a note of caution, care must be taken to trace out the vein and be prepared to lose the foliage fed along the vein's pathway."

An interesting characteristic of potentilla is that the tree seems to grow with a combination of live veins twined together. This produces interesting natural deadwood veins. Jerry Vlcek refers to the trunk of potentilla as "ropey" since it resembles a rope; a result of several shoots (strands) combining to form the rope. He also feels that these multiple trunks are a response to a stressful environment (wind, drought, minimal soil and nutrients) and fewer shoots appear when grown in sufficient soil and water. This feature may make it easier to reduce a heavy area by removing one or two of these veins. Care must be taken to examine which vein is feeding which branches, and only remove those that can cause the least amount of damage.

Drawing from this growth characteristic of potentilla, Jerry Vlcek has suggested the wrapping of several individual shrubs together, thus reproducing the twisting affect of wind, to form a larger trunk. That will be the subject of one of this spring's experiments.

Another feature of potentilla, related to its twisted vein growth, is the poor healing over of large pruning cuts. A small cut on a growing vein will probably callus over, but a large cut of an entire vein or large branch will probably die back without any callusing. I have found that when removing an entire vein or large branch, it is better to carefully rip it off creating a more natural dead wood area. But you should be careful about this so that you don't rip off the living parts of the tree that you want to keep. "(There is an excellent article illustrating this topic in "Bonsai Today" Number 83 - 2003 #1 by Felipe Recio titled "Veins: The Life of Trees.)"

I treat dead wood areas with lime sulphur mixed with a drop of black acrylic paint to darken the jin and give it a more natural appearance. I usually leave on the old shaggy bark because it suggests an older tree, although you could consider removing bark to show the interesting swirls often created in the natural twisting trunk. I think this design consideration should include whether or not the trunk swirls complement the nature of a given tree.

The tree is currently about 7¾ inches tall, 5¼ inches wide and a 2½ inches diameter at the base and living in a Japanese container (kiln unknown). For deciduous trees, I prefer glazed containers, deferring to the transient and delicate nature of the leaves. For colors, blues seem to work well with brown trunks, green foliage and moss. Dark blues have the added feature of contrasting with yellow flowers. John Biel sometimes uses glazed and earth toned containers.
Care and Maintenance
Regarding the care and maintenance of potentilla, the Toronto Bonsai Society printed an information sheet for the Bonsai Clubs International convention in Toronto 1997. It recommends repotting the tree in the spring in a well draining soil enriched with dolomite limestone. "Rocky Mountain Wild Flowers" by A.E. Porsild (1974) noted that potentillas are generally found "on calcareous (containing calcium carbonate, calcium or lime - DJ) soils."

Potentillas need to have a moist root environment. This can be achieved by watering more frequently, planting the tree in a deeper pot or adding more organic material to the soil mixture. Sphagnum moss cut into one-inch pieces could also be placed on top of the soil to reduce surface moisture loss and protect surface roots. I have often come home after a hot or windy day to find the foliage drooping a little, but they perk up after some misting and then some water. Potentillas are grown in full sun and are very winter hardy.

The TBS sheet recommends fertilizing every two weeks with 20-20-20 and then a lower nitrogen amount for an established tree in maintenance mode. Regarding pests and diseases, the write-up says "None have been noted in bonsai culture."

The small leaves, flowers, availability, winter hardiness, relatively quick branch development, natural movement in the trunk and branches plus areas of deadwood, make potentillas a good candidate for your bonsai bench.

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1 commenti :

  1. I love bonsais, my florist made me a bonsai lover by gifting me every Christmas with it.

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