Limestone Wattle Blues

Acacia caerulescens, otherwise known as Buchan Blue or Limestone Blue Wattle is endemic to a small area in East Gippsland, Victoria.  It has been listed as a vulnerable species with fewer than 2,000 mature specimens in the wild, and is the subject of a National Recovery Plan.  It is associated with heavy soils on limestone country in its natural environment.  It was described as a separate species in 1989.

When we moved to our present house (in Stirling, ACT) in 2010, most of the front garden was quite barren, with its soil covered in wood chips and dominated by a vigorous blue gum (19 metres tall) with three or four smaller, non-descript trees to keep it company.

I planted a few native plants in 2011, among them were two Buchan Blue seedlings.  At the time I did not know much about growing this very intriguing species.  Anyway, the two seedlings grew very quickly, faster than almost any other tree seedling that I had ever grown.  2012 was wetter than average in autumn and spring, and when we went to Adelaide for a few days, they both looked healthy and vigorous.

Screen Shot 2016-08-10 at 7.00.30 PM

On our return, the first surprise awaited:  one of the seedlings was dead, as dead as a doornail.  I pulled it and it came out of the ground easily.  The roots were losing their “bark” (epidermis) and there were no finer roots.  It seemed to have succumbed to a root rotting fungus.  On reflection, this was not surprising since the soils over limestone on which it typically grows would be relatively free draining, so that susceptibility to root pathogens might be suspected, as is the case with Wollemi Pine which comes from sandstone country, also free-draining.  In contrast, this part of the ACT is quite flat with undulating topography, probably quite a suitable habitat for root rotting fungi.

The remaining plant continued to grow rapidly until 2014 when it was about 1.5 metres tall and then one windy night, following a rainy day, disaster struck again – the tree was blown over.  Its roots seemed to be concentrated near the surface, taking the easy path along the decomposing layer under the woodchips.  Nothing daunted, I got a friend to prop it up and to cut off the upper third of the stem, thereby lowering its centre of gravity.  Since then the sapling has grown into a vigorous, handsome young tree with attractive blue grScreen Shot 2016-08-10 at 7.00.43 PMeen phyllodes, apparently without problems, apart perhaps from loneliness.  It has pale yellow flowers which appear in spring.  So far at least, the flowering has not been prolific nor long-lived.  Also, there has been only a little evidence of a leaf destroying organism as reported from the National Arboretum, Canberra (Forest 13/99).

Our tree is now about 7.5 metres tall (April 2016).  What can we conclude from our experiences?  Firstly, when growing rare and endangered plants, remember that there are reasons for their rarity which will probably make them hard to grow.  Secondly, Buchan Blue is a beautiful, fast growing tree that may well have a place in landscaping – if you can overcome unexpected difficulties.

Tony Fearnside

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