WIRING PRACTICES (Part II A)
Wiring practices is an important subject that requires detailed explanation to make the message clear and precise and considering the amount of pages required, (10-12) which in reality is too long for a single post, (5 pages max) it will be divided into 2 sections A & B. apologies for any disappointment caused, but it is imperative that what is written covers the topic thoroughly especially for the beginner.
In part 1. a discussion was held on climate zones and the temperatures that effect the fauna endemic to those regions in addition, shrubs or trees from warmer climes can be cultivated in colder regions providing they are kept in warm temperatures during the winter months. Also discussed was the difference between softwood (conifers) and hardwood (deciduous) and how their cellular structure differs in the amount of flexibility within a particular species; Scots pine Pinus sylvestris a conifer very pliable and a Japanese maple Acer palmatum extremely rigid.
Bending or pre-stressing
Continuing on from part 1., a tree pre-stresses its trunk and branches quite naturally as it has to combat the forces of nature, more than 90% of a tree’s cells are long thin- walled tubes closely packed together, arranged along the direction of the trunk or branch.
Their function is to transport the nutrients and water from the leaves (Phloem) and roots (Sapwood) respectively. They also provide support because, no matter which way a trunk or branch is bent, the internal forces always act parallel to the cells and are able to adapt to tension and compression. In addition, because the cells are hollow, the tree’s trunk and branches can be thicker as opposed to it being a solid mass.
However, when bending the cellular structure of the xylem becomes disrupted meaning the outer radius of the bend will be in tension whilst the inner radius is held in compression. With conifers this is not so much of a problem but with deciduous, the chances are that the branch will either snap at the weakest point or actually break away from the trunk if not supported.
In addition, if a bend is too severe, the cortex may splinter or break resulting in damage to the phloem and a damaged phloem is not just open to attack from Lepidoptera and Fungi, it can disrupt the movement of nutrients. Therefore any bending should be done in stages to eradicate such problems and this can take several growing seasons depending on the species.
Another point worth considering when shaping a tree, is the container in which it is kept. Applying minor bends to a tree in a pot is not too much of a problem as the root ball should stay undisrupted if wired in. But for heavy or serious bends the tree should be moved to a wooden box and wired down for stability. If one recalls the Scots pine image shown in part 1. one denotes that the container is a wooden box and the advantage of using a wooden box is that any supporting guy wires are easily attached, which is not really feasible if using a clay or plastic container.
Bending thicker branches requires a more careful approach due to the amount of tension being created to the outside radius. To create such a bend the following method usually suffices.
wet raffia is tightly wrapped around the bending section making sure the area either side of it is also protected
tape a length of heavy gauge wire to what will become the outer radius of the bend to protect the bark, cortex and phloem from splitting
wrap the entire area in rubber tape
select the correct gauge of wire and apply it to the proposed bending area
carefully bend the limb or branch into position and use guy wire if necessary
Often when bending thick branches some practitioners resort to other methods when wire alone is insufficient to hold the desired shape. These include Heat – using a heat gun or gas burner to soften the cellular structure on the intended area. Splitting – cutting the branch in two halves and reducing the heart wood, these are then joined together and the bend is made. Channeling or grooving – cutting a groove or channel into the branch to remove the heart wood, thus resistance is reduced allowing the branch to be shaped. Such methods should only be carried out by professionals because such surgical practice requires much after care to maintain the tree’s health and eradicate potential disease.
Another simpler method when bending branches is the ‘V’ notching technique as shown below: Small angle cuts A, B & C an inverted ‘V’ are made in the branch into the heart wood but not beyond, these ‘V’s cuts are then closed as the branch is bent down using guy wires attached to the container preferably wooden.
However, this practice does require some thought prior to undertaking because, any wounds not closed completely will have difficulty in healing, which can cause the disruption of nutrients and moisture not only to the wound, but to other areas moreover, wounds are susceptible to attack from disease. But some disagree, it is said that a conifer’s natural defence system will heal the wounds via it’s resin or sap and there is a logical argument here. Trees do have the ability to heal wounds and some species are more resilient than others nevertheless, it only takes one pathogen carrying insect or fungal spore to infest a wound.
How then do we protect such wounds? With the more intense methods mentioned above, cut pastes and various elastic and rubber tapes are available to facilitate repair. With ‘V’ notching the same can be used but most horticulturalists simply apply ‘vaseline’ (petroleum jelly) to the wounded area.
Generally speaking these are relatively slow growing often with rough bark and can be wired and left for a considerable length of time 3 to 5 years or more depending on the species and any wire marks are hardly visible. But there are conifers with smoother bark for example, common juniper, juniperus communis noble fir, Abies procera and larch Larix spp. Thus, it pays to be vigilant and check any wire applications periodically especially with young trees and those with smooth bark. Another important factor when wiring conifers is to avoid trapping the needles because not only is it unsightly it prohibits them from functioning properly.
Deciduous varieties (although some have rough bark oak Quercus spp. willow Salix spp. and black poplar Populus nigra) most have relatively smooth bark and any wire applied if not checked will cause unsightly indentations that are difficult to eradicate, hence the specimen becomes useless as a bonsai due to its ugly appearance; so why does this happen to deciduous species and not so much to conifers?
A conifer being ‘evergreen’ slows down its activity in the colder months but still needs to transport moisture to the leaves (needles) for without it they would wither and die, thus a conifer does not become dormant in the true sense of the word and when spring arrives normal activity is resumed.
Deciduous in autumn shed their leaves, hence there is little need to pump quantities of moisture, thus the tree slows down and dormancy begins. In spring new activity commences with a growth surge referred to as ‘sap-rising’, as regeneration of new foliage and growth is the plant’s main focus. Therefore, deciduous trees should not be wired during ‘sap-rising’ and any wire applied the previous autumn must be removed.
When then can wiring begin?
The general consensus is that conifers can be wired after the growth surge from midsummer to early autumn as most new growth will have been made which may require wiring to retain potential shape. Any damage or slight mishaps made during this time will heal more quickly as the plant is getting ready for the coming colder period.
Deciduous species should be wired into shape during the late autumn when the tree has shed its leaves and the potential design is more visible as this period allows the branches to set. However, they can be wired during the summer months but, any wiring must be checked on a regular basis to avoid indentation.
Wiring saplings grown from seeds
Arguably for the novice one of the easiest plants to grow from seed as potential bonsai apart from Citrus spp. lemon, orange and lime is the pomegranate Punica granatum. Pomegranate seeds do not require stratification and can be sown straight from the fruit, providing any pulp residue has been removed to avoid the threat of fungal pathogens.
After 4 to 6 weeks they will sprout depending on cultivation conditions and after the cotyledon (embryonic leaves) have matured the plant produces pairs of leaves at intervals that are opposite, glossy, narrow and oblong and once large enough to handle, they can be transplanted into 14cm diameter pots, a size needed due to vigorous root growth.
Once the plant reaches 12 to 15cm in height the stem starts to lignify (become woody) at the base, but is still ‘green’ towards the top and it is at this stage the plant can be wired. For a tree of this size, you will need approximately a 40cm length of 1mm diameter aluminium wire. Thread wire the up from the base of the pot staying close to the stem and put a bend or tag in the wire on the pots underside to stop it from moving as shown below.
Gently wind the wire up the stem using loose wider coils, if the wire is too tight indentations will appear quite quickly (within 2 -3 weeks) and will have to be removed. As the diagram shows the wire protrudes higher than the plant’s apex, do not cut the wire because as the plant grows the extra length can be used for continued wiring as opposed to using a second piece of wire. Once the plant has attained the desired height and the shape has set, the top of the leading stem can be removed and the wire cut accordingly.
Young pomegranate saplings are quite delicate in their first few months of growth, thus care must be taken when manipulating them. Hence it might be prudent to draw a quick sketch of the intended shape or design and then apply just one set of bends as opposed to continuously bending the plant. Wiring very young trees or shrubs can be considered as a useful addition to one’s learning curve, because it is a stepping stone to more mature trees, nevertheless one has to be careful with relatively ‘green’ material.
The image below depicts a pomegranate an example of what can be attained in a short space of time 3 years, with the basic shape achieved within the first year. Obviously the tree requires further work before it can become a potential bonsai. So until next time when we continue with ‘part B’, BW, N.