SIZE CONTROL OPERATIONS IN GARDEN EUCALYPTS: SCULPTING EUCALYPTUS GUNNII (II)
   
               
               
   
Observation of the early growth of Eucalyptus in your garden conditions is very important to later take appropriate decisions. Fast growing species do really go fast. After being planted by spring this Eucalyptus specimen pictured below nearly doubled in size in just 10 weeks, up to almost 3 meters during summer and autumn before the first frost event. Its good growth rate, the formation of protective fibrous bark in the lower trunk and the depletion before winter of the extra slow release fertiliser added at planting hole secured its survival. Absolute minima during winter reached -7ºC, considered mild for a species like this that can take down to -15ºC without harm, meant that frost damage was absent even on the newest growth (see Photo 1).
   
               
Eucalyptus gunnii pruning / Poda en Eucalipto guni
   
Photo 1: Sequence of winter-spring growth in Eucalyptus gunnii, showing a first pollarding intervention by mid spring once the risk of late frost events is considered low
   
               
               
   

This specimen tree was planted in a small garden plot at a distance to surrounding infrastructure smaller than recommended (3 to 5 meters) to avoid potential problems caused by root expansion or by wind blow. Its fast growth was noticeable (see "Early Growth"), but did not mean unestability during the first year. However, being planted facing West and having a shade casting obstacle to the East meant a tendence to lean towards the light. Perspectives for future problems an were excessive leaning plus strong winds and potential damage by root system to built areas nearby, as any naturally big sized tree could cause in this situation. It was decided this tree should be subject of measures to control its fast growth, trying to keep it smaller sized to reduce both potential problems (windthrow and very fast root colonisation) as much as possible.

As most Eucalyptus do not really go dormant but barely sleepy during winters in cool temperate climates, size control operations carried on immediately before the start of frost season or too early by spring can easily increase the risk of bark detachments near cutting edges after you prune some parts (late autumn) or damage on the fragile newest growth (late winter), especially if daytime temperatures regularly go over 8ºC. A first pollarding (removal of top growth) combined with maintenance pruning (clipping of terminal buds on some side brancheis) was delayed until spring, once the risk of damage by late frosts was minimum. An additional severe pruning of lower side branches was considered but discarded, since added to top growth pruning it might remove an excessive amount of the leaves the tree will need to photosynthetizise during its second year in the ground and keep growing fast.

Recommended Eucalyptus tree age for a first pollarding intervention ranges from 2 to 3 years, but this timeframe must be considered flexible depending on circumstances for each particular garden. For slower growing species, pollarding too soon means weakening a yet not fully established plant, but for very fast growing ones it can mean the tree has already discarded some of its lower branches by itself so and appropriate pollarding height must be quite high, which can make future operations more complicated. For our case, we considered pollarding by the beginning of its second year in the ground.

The selected target for these tree size control operations is producing a small tree from 3 to 5 meters height with compact form and as dense canopy as possible (see Photo 5). . Pruning height was established at 1.5 meters height. From here, side branch growth will be encouraged in order to obtain several sturdy leaders as divided as possible to create a compact crown effect. Low pruning of lateral branches will be necessary in future to give the main trunk a clean outlook.

   
               
   
Eucalyptus gunni pruning / Poda en Eucalipto guni
Eucalyptus gunnii pruning / Poda en Eucalipto guni
   
   
Photo 2: Scissor pruning cut, a clean oblique edge facing South
Photo 3: Clipping on some side branches will encourage additional compact growth
   
               
   

One of the advantages of pollarding one year old branches is that woody tissue has not yet fully developed, making pruning scissor cutting an easy task and securing clean cuts that do not damage surrounding bark (see Photo 2). An optional protective measure can be taken by temporarily dressing the fresh cut with a piece of clean textile previously submerged in a solution of water and a fungicide and tying it firmly some inches below the cut.

It is expected that below the pruning cut some of the side branches will take dominance during the second year of growth, preferably if on the upper side of the now pollarded main trunk. However each tree is different and careful observation of its main branch architecture is needed. Those few branches we have expectations to become dominant should be let grow at their own pace and can be taken care for later during future pruning operations. But those at mid and low height once they reach a chosen length can be encouraged to grow “bushy” by clipping of terminal growth buds (see Photo 3), preferably if there are already newer branchlets growing from axillary buds immediately below. By clipping, two or more of these will concentrate growth and create a more compact effect within the next months.

   
               
   
Eucalyptus gunnii pruning / Poda en Eucalipto guni
Eucalyptus gunnii pruning / Poda en Eucalipto guni
   
   
Photo 4: Pollarded top is a source of branchlets for flower arrangements
Photo 5: Example of finished sculpted E. gunnii tree after repeated pruning and clipping
   
               
               
   

Removed branches are not waste. Up to 25 branchlets harvested from pruned top growth have been successfuly added to flower arrangements. Its vase life without preserving methods can be of up to 3 weeks. However it is important to note that this pruning scheme is not targeted to maximise marketable foliage production. In future instalments we will see how this tree adapts to the removal of top growth during its second year and how much useful the development of secondary leader branches is for further sculpting.

   
               
       
               
       
               
 
 
 
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© 2006 Gustavo Iglesias Trabado / GIT Forestry Consulting