How fast do Dicksonia antarctica tree ferns grow in the UK - the saga continues

On 4 April 2014 I published a update on the growth rate of the Dicksonia antarctica tree fern in my Plymouth garden.  Two years and three growing seasons further on it's time for another update.

Measured this afternoon in now stands at 46.5 in / 118cm from ground level to the height of the growing point.

Dicksonia antarctica in the rear garden 20/10/2016

This represents a fairly moderate slowdown in growth since I last reported.  Graphically it can be represented as follows:

Dicksonia antarctica trunk growth rate in inches

Still not too bad.  There are many shrubs and dwarf conifers that can't manage this amount of height extension despite ultimately growing larger than the Dicksonia.  It can probably be explained by two factors.  Firstly trunk extension is being matched by a increase in trunk girth and this all takes energy. The fronds are larger and heavier, requiring a thicker stem for support, so the earlier growth spurt is beginning to diminish.  Secondly, watering and feeding has been reduced over the last couple of years.  I've had other preoccupations and constant attention has diminished.  Taken together, growth has slowed a little.  Still encouraging, though.  Plant a number of young (cheap!) sporeling ferns in a lightly shaded spot, nurture well and 15 years later you could have a grove of specimen plants with nearly 4ft stems and their palm like rosettes of fronds.