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Developing good roots

Lawrence Burgess discusses ways to develop good roots and looks at why the masters design a tree from the ground up.

Introduction

We can define good roots as; "Strong surface roots, of differing thickness, radiating out, at irregular intervals, from all around the base of the trunk. Below the soil surface the roots subdivide into a secondary and tertiary network." The surface roots must impart a feeling of stability to the tree. (Fig. 1)

 

roots-fig1

Fig. 1

Roots, as we know are directly proportional to the amount and type of ramification that we find on the top of the tree. Fine roots usually produce the fine tertiary growth we seek as a part of the refinement process. The depth and spread of the root system, also balances the height and spread of the branches. Not only is a good spread of roots important to the tree, but healthy roots are also obviously necessary for a healthy tree.

The best way to get good roots on your tree is to start with a tree with good roots. This, however, is not always possible and therefore we must find ways to develop good roots. In bonsai we do not need a tap root, which in the main, functions as an anchor for the tree. We, instead, prefer to develop an adventitious root system to enlarge the volume of feeding roots.

SURFACE ROOTS (Nebari)

(i) Cuttings

Dip the cut in a good rooting compound so that good all round roots develop. Strike the cuttings in sharp river sand or quarry dust.

(ii) Nursery Stock

When you bare-root nursery stock, comb out and untangle the long roots. Remove all the damaged and dead roots and the tap root if there is one. Also remove as much of the heavy roots as you can without endangering the health of the tree. Be careful not to harm the light roots. Plant the tree in a wide, shallow container, using an open soil mix with plenty of sharp sand to allow the severed roots to sprout.

To develop good, strong surface roots, cover them well and keep them covered for at least two years. Junipers and pines may take longer. This is especially true for elms that should have its roots covered by at least 2cm of topsoil. The exceptions to this rule are figs that should have the top of its surface roots uncovered for rapid development.

(iii) Trees with one-sided roots

(a) At times cuttings or nursery stock have one-sided roots. Improve this by wounding the bark where you want roots to generate. You can cut flaps in the bark and place a tiny pebble under each flap, apply a rooting hormone and cover the wounded area with moist soil. Alternatively, drill small holes in the bark where you want the roots. Dip matches or toothpicks in rooting hormone and insert one in each hole. Cover the matches with moist soil. (Fig. 2)

roots-fig2

Fig 2.

(b) Deborah Koreshoff describes the following method for surface roots:

Cut a plate of asbestos or hardwood in the shape of the pot, but about 5 cm smaller. In spring select a tree with good root distribution around the trunk and no tap root. Bare-root the tree and gently force the roots into a horizontal plane without breaking them. Place the tree on the board in the position in which you intend to plant it in the container. Arrange the 'roots in the most pleasing manner and try to lay them as flat as possible. Tie them to the board with string without damaging the bark. Plant the tree in the way previously described under section (ii). (Fig. 3)

roots-fig3

Fig. 3

(c) If you have the skill, you can approach graft an attractive root in a position where you need it. The best time is spring or early summer. Use well-established two to three year old seedlings. Cut away the bark and heartwood from the sides of the seedling to form a "V"-shaped wedge. Also carve a matching "V"-shaped groove into the base of the tree, at the site you want the root. Make sure that you match up the cambium layers of the seedling and the recipient tree and bind it securely. (Fig. 4) Seal all grafted areas well. Leave the grafts for at least one growing-season before inspecting them. It takes a great amount of skill to do a job that is artistic and natural looking. However, the advantage is that you gain mature roots immediately and they can also be placed in perfect positions.

roots-fig4

Fig. 4

(iv) Root development for particular styles.

To develop the long roots for ishizuke, the root-over-rock style, plant the tree with the rock in a deep black bag using an open soil mix. A good idea is to put the soil only around the base of the rock and then to put the tree in place on the rock. Fill the bag with small gravel chips. The method for developing surface roots, described above, applies. Repot the tree every two years and trim all the fine roots from the upper parts of the main roots. The exceptions to this are elms and figs, if their roots have not developed sufficiently in two years they will rarely develop much more over a longer period.

The planting is only watered once or twice a week. This increases the elongation rate of the roots because the gravel dries out while the soil at the base of the rock retains moisture. As we know, roots are strongly positively hydrotropic and will go in search of water.

Use the same technique to develop the roots for ne-agari, the exposed root style. An exception is ' that we use a very deep black bag (400-500mm). After the first year, gradually expose the roots a little bit every year and remove the soil/gravel from between the roots. Repeat this until you have exposed the whole planting to where the roots enter the soil at the bottom of the bag.

A tree with a leaning trunk, shakan, in nature has usually fallen foul of the forces of nature. That is, it has been blown over by the wind or wind or water has partially eroded the soil around the base of the tree. To create a natural looking leaning trunk, we must look at what happens in nature. Surface roots of a leaning trunk are subjected to certain forces. On the side away from the lean the roots are under tension and are relatively straight from the pulling action of the lean. The force of the lean compresses the roots under the lean and develop kinks or "knees". To get a more realistic leaning trunk, wire the roots into these formations. (See Fig. 2 in Leaning Trunk)

Plant a tree for kengai; the cascade style, in a porous, clay, "soak away" pipe. Plant the pipe in open ground at an angle of between 30° - 45° off the horizontal. The pipe contains the spread of the roots to a narrow, cylindrical mass. We need this for the container in which we plant the cascade style. A cascading tree's roots are subjected to similar forces to the roots of leaning trees and the same rule applies. After the second year the roots should have developed sufficiently to pot it into a bonsai container.

2. Fibrous Roots

(i) Soil

The soil you use is very important for root development and seems like the logical place to start. Bonsai soil should drain rapidly enough to prevent root-rot, but it must also retain enough moisture to meet the needs of the tree.

A main ingredient of bonsai soil, is sand and by varying the proportion of sand you vary the drainage and water retention characteristics of your soil. A mixture of 2mm to 6mm grit is ideal, depending on the size of the tree. The more sand, the faster water will drain and it retains less water for absorption through the roots.

Another aspect of sand that is important for root development is the type of sand used. Always use sharp river sand or sand from weathered or crushed rocks. Fig. 5 shows the importance of sharp sand, as opposed to a smooth, round sand-particle. When a growing root encounters a smooth, rounded sand-particle, it goes around it. With a sharp sand grain the root splits and will do, so with each encounter with a sharp sand particle. The finer sand-particle produces a finer root structure. The division and subdivision of the roots create the fine ramification that increases the volume of feeder roots. This encourages the fine tertiary twiggage we are trying to achieve as we refine our trees.

A correct balance of soil ingredients is very important for the development of good roots.

(ii) Pruning

Root pruning has some distinct advantages for the plant.

  • It relieves the congestion in the container, improving the porosity and circulation of water and air.
  • Pruned roots react by replacing the old dysfunctional roots with a mass of new, active feeder roots.
  • As with the fine twigs that develop by pruning and pinching back top growth, root pruning also promotes the development of finer roots.
  • While the tree assumes the more revered appearance of age with passing years, it can have a perpetually young root system.
  • You can study the condition of the sub-surface roots and detect pests, damaged, or diseased roots.

BIBLIOGRAPHY

  1. Adam, Rudi - Bonsai in South Africa, Struik Publishers, 1994.
  2. Adams, Peter D. - Bonsai Design, Japanese Maples, Unwin Hyman Ltd., 1988
  3. Koreshoff, Deborah R. - Bonsai, Its Art, Science, History and Philosophy., Macmillan, South Africa, 1984.
  4. Naka, John Yoshio, Bonsai Techniques II, Dennis Landman Publishers, Santa Monica, Ca.

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Haiku

Sunlight dripping from tree

Slides off the periwinkle

And splashes on ground

Random Bonsai Tip

If surface roots are unequally spread around the trunk or if they are lacking completely you can drill holes and insert match sticks or make deep scars around the base of the trunk on the side where the roots are needed below soil level. Apply hormone powder and sphagnum moss; cover with plastic and keep moist. Leave for 6 months to 1 year for the roots to develop.