The only way to tell is to take a measurement now and do the same in a year or two to compare. There are three main things to measure when looking at trees - girth, spread and height.
Girth is the circumference of a tree and is measured at ''breast height'', or 1.4m above ground level. This is easily measured by wrapping a tape measure around the trunk.
Spread is the full width of the canopy out to the drip line and this is usually done in two measurements: a north/south measurement and an east/west measurement. This is not always possible due to other plants or buildings, but take measurements in a couple of directions then average them.
Estimate height by folding a square of paper in half diagonally to create a triangle. Then with the right angle furthest from your eye, look along the longest side of the paper, keeping the bottom of the paper horizontal with the ground.
Move towards or away from the tree until you are looking at the highest point of the tree. Then measure from where you are standing to the base of the trunk and add your height to give you the height of the tree.
With these results you can take the guesswork out of whether that tree is getting too big or answer the question ''If that tree falls over, will it hit my house?''.
- Dylan Norfield is the collection curator of the Geographic and Arboretum collection at Dunedin Botanic Garden.
