Training and Pruning

 

Why and How to Pollard Eucalyptus Trees

In this section you will find information on the following:-

General notes on pollarding

Pollarding Eucalyptus

Age of tree at pollarding

Technique and Timing

General Notes on Pollarding
Generally the activity of pollarding is done to reduce the overall height of a tree or shrub to less than they would grow naturally.  It is done once a tree has reached a considerable size.  It has to be carried out every few years thereafter and may be on an annual basis, to keep the tree at the desired height.

Common tree species that undergo this technique are Willows, Lime, Oak, London Plane and Eucalyptus.  In particular, it is used to rejuvenate Oaks of 300 years of age or more, that are showing die-back in the canopy.  By reducing the crown, the root system is relieved of some of its work and the tree responds by producing new vigorous growth. As a result the whole tree becomes healthier in its twilight years.

It is a serious job, usually involving working at height and is best given to a tree surgeon to carry out. Very often, this is  a case where one needs to choose the right tree for the location, prior to planting. However, pollarding is frequently carried out on mature neglected trees that a householder has inherited, as a result of acquiring a new property.

The process involves leaving the main trunk untouched and pruning off the crown of the tree leaving the main five or so branches. These are also reduced in length and after several weeks or so, new shoots emerge from the ends of the main branches and in the case of Eucalyptus, very often up the trunk too. The new shoots emerge from meristematic tissue just under the bark and are loosely secured to the old branch structure by callous tissue. The adhesions lignify and strengthen with the passage of time, as the tree lays down woody tissue.  

Eventually with repeated pollarding sessions, the tree takes on the charactaristic swollen head of a 'pollard' as seen in many town and city streets (think wind in the willows Salix trees).

Pollarding Eucalyptus
Eucalyptus are pyrophytes; they have the ability to regenerate after forest fire. One of their survival adaptations is that they have a great deal of meristematic tissue lying dormant  in their cambial layer, deep under the bark.  Released from suppressive growth hormones in the shoot tips of branches, this tissue quickly develops epicormic shoots just below the pruning cut, a couple of months after pollarding.  The leaves on these new shoots will pass through the juvenile stage very quickly (they may miss it out altogether), fly through the intermediate phase and reach adult foliage.

The new shoots soon re-establish a tree canopy with a network of branches, but very often one shoot will become dominant, suppressing the development of the other shoots.  Pollarding can be a short term solution for a fast growing Eucalyptus species, but genetically they are geared towards the fast and furious end of the spectrum; more Hare than Tortoise.  

With fast growing species, the tree will quickly grow away again and may need pollarding annually to be kept under control.  Fast growing species that would undergo the practice would be

E. dalrympleana, E. deanei, E. glaucescens, E. gunnii, E. nitens, E. obliqua, E. regnans, E. rubida and E. urnigera.  These species want to produce a very straight trunk, tend to drop their lower branches early on in life and so the crown of the tree rises up the trunk very quickly.   Pollarding reduces the height of the crown again, forcing the tree to form branches lower down,  just below the cut.  The crown is the point at which the main branches begin to sprout from the trunk.

Age of tree at pollarding
The tree needs to be over two years old when first pollarded, otherwise it may not have enough energy stored to facilitate regeneration.  Beyond eight to ten years when pollarded, Eucalypts will look a little challenging until they have re-grown branches with a substantial amount of foliage..

Technique and Timing
The best time of year is Spring, from the middle of March onwards.  Using a very sharp saw or loppers, prune off the trunk 1.8 to 3 metres (6-10ft) from the ground, with a sloping cut, (facing South, so the sun helps to heal the wound). Treat the cut with pruning compound. Leave any side branches and leaves on the tree;  this encourages sap to rise up the trunk and feed the dormant buds.

We currently have no experience of the long term effects of annual pollarding on young Eucalyptus trees, but will be carrying out trials at our nursery.

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