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Winter pruning

by Eugenie Sohnge

According to the Chambers Dictionary PRUNING comes from OFr proignier - origin unknown; it is a transitive verb meaning to trim by lopping off superfluous parts; to remove anything superfluous from - ; to remove by pruning. For our purposes we can describe winter or maintenance pruning as a never ending cycle of replacing old with new.

Why should we prune?

Well, without pruning the tree will lose its artistic shape and to maintain the shape of a tree we must equalize the strength between the parts. So, to balance this growth we need to work on the tree in the dormant period by pruning unwanted or too long branches and in the active growing season by pinching back young shoots to promote leaf reduction and to shorten the internodal length. A cautionary reminder - you must maintain a balance between the branches and the roots and this is done when a tree is repotted - not part of this article.

In winter when the tree is dormant and when deciduous trees are bare there is time to study your trees to see how they have developed over the last few seasons. It is an ideal opportunity for design improvement and it is also a renewal technique, which allows you to grow new branches where needed.

Drastic winter pruning on some deciduous trees (like beech, elm) will promote the development of buds all over the trunk and branches. However, you must remove the unnecessary buds immediately to prevent loss of vigour and future scarring left from removing unwanted branches.

Generally speaking, the strength of the tree is concentrated in the apex and the tips of the branches and this can be seen in the larger size of the buds at the tips. This strength must be balanced, and you do this by cutting back on the strongest branches and allowing the weaker ones to develop. Pruning stimulates and directs the growth of the tree and hormones play a Significant role in new growth. If the terminal bud is trimmed in late winter the tree doesn't have enough time to re-establish the concentration of the more dominant hormone auxin in the new terminal bud. Then another hormone, cytokinin, will promote side growth so the growing strength is spread throughout the tree.

To recap WHY we should prune in winter:

  1. Winter prune to maintain the shape or design of the tree. You can correct faults like bar or parallel branches, ones that cross over or are too long or grow in the wrong direction. Make sure the branches are in proportion to the tree.
  2. Pruning produces smaller leaves; it reduces the internodal length and therefore it induces dwarfness.
  3. Pruning allows us to develop fine ramification which will also promote density of the foliage and maintain neat foliage pads.
  4. By pruning back the inner branches are prevented from dying because trimming back tips distributes the growth impetus evenly to all branches and subbranches, ie. diverts the growing energy to the weaker branches; it encourages ventilation of the interior of the tree.
  5. Pruning allows you to control the apex and so avoiding it becoming too thick and dense.
  6. Pruning can be seen as grooming, making the tree neat and tidy - by removing the older and dead growth you also prevent overcrowding and you make room for the next season's growth to extend.

When to prune?

When do we do winter pruning - in winter of course! Yes, but WHEN in winter? Too early in winter is not good because the healing process is slow in the dormant period, also if you prune to early you can cut off the downward movement of stored food from the branch lets to the trunk and root system.

In the southern hemisphere from about the end of May we can start looking at our trees in their winter dress or undress and we can start removing the old berries, seeds and fruit and also brown needles.

Late in winter, from June to August, before new shoots appear and when the food, stored in the roots, hasn't yet started moving upwards to the growth areas is the right time to prune, because you won't be wasting nutriments. By the end of August when the buds start swelling it is time to repot and at the same time to trim roots and branches.

How should we prune?

First of all, be careful with cutting off large branches in winter - they could die back. Rather trim them back leaving a short stump, which can then be further removed in spring.

Where the rest of the branches are concerned, prune back to buds facing in the desired direction of growth ego maples have opposite and elms alternate buds. Remove buds growing up or down. Don't cut too close to the buds in case you break or damage an important bud. Thin out the branches that are too dense so that they open out in a V-shape, and shorten the remaining branches to 1 or 2 nodes. If the apex is too thick substitute a smaller branch growing near the apex. Cut twigs and branches at an angle away from the bud, not too close to the bud, make sure it is a clean and neat cut and always use sealer or cut paste to promote healing and prevent infection.

What Tools to use?

  1. Pruning shears or trimming scissors for smaller branches.
  2. Concave branch cutter for bigger branches.
  3. Knot/knob branch cutter, which leaves a spherical cut.
  4. Root pruner is useful for heavy duty pruning.
  5. Saw for really big branches.

Which trees must be pruned?

All trees must be pruned to some extent. However, older trees need less pruning than younger trees. Deciduous trees can be cut back to bare wood and will sprout on old wood. Evergreens don't store large quantities of food so be careful with pruning.

Finally a tree should be strong and in good health to withstand pruning - it is a wound you are inflicting! And remember you can't put back what has been cut off - so approach pruning with sensitivity, common sense and a spirit of adventure.

Bibliography

Bonsai, no. 33, 1997, p.20-4

Bonsai Today, no. 44, 1996, p.55-9 Bonsai Today, no. 58, 1998, p.40-4 Koreshoff, D, Bonsai, Its Art, Science, History and Philosphy,1997. Ch.2.

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