In Focus - Blue Mountains Botanic Garden

Red Wattlebird feeding on nectar produced by the magnificent Puya alpestris ssp. zoellneri (family Bromeliaceae)

SENSE & SENSIBILITIES

SUMMER AT THE BLUE MOUNTAINS BOTANIC GARDEN IS AN ENTICING TREAT FOR THE SENSES. SENIOR HORTICULTURIST MARION WHITEHEAD TAKES AN IMMERSIVE TOUR.

From the structure of deciduous trees revealing themselves in winter to bright bulbs poking their heads above ground in spring, different seasons offer very different ways to immerse yourself in the garden. Summer is no exception, especially at the Blue Mountains Botanic Garden, where visitors are surrounded by all manner of sensory experiences.

SMELL There is nothing like the smell of rain falling on a summer day. In 1964 two Australian scientists working at the CSIRO published the first scientific description of that odour and gave it a name: “petrichor” (from the Greek “petra” for stone and “ichor”, the blood of the gods). Petrichor is caused by a soil-dwelling bacterium creating a chemical compound called geosim as it breaks down organic matter in the soil. The smell has been shown to improve our mood, with our noses able to detect the scent of geosim in the air even when diluted to parts per trillion.

SIGHT In the cool, dark Gondwanan Garden which many visitors retreat to in the heat of summer, the ferns appear to glow in the early summer afternoons. This is due to what is known as the Purkinje Shift – an adaptation like night vision that means in lower light conditions our eyes become more sensitive to the blue end of the colour spectrum, making green colours appear illuminated. The effect can only be experienced through your eyes and not the lens of a camera, making it a great opportunity to take a breath and enjoy the moment.

SOUND Thanks to its volcanic soil, Mount Tomah has some towering trees, particularly the

‘Gunnera leaves feel like rough, uneven sharkskin’

local Eucalyptus fastigata. And if you put your ear to the trunks of these tall trees on the hottest summer days, sometimes you will hear a strange ‘popping’ noise. This is the sound of cavitation, as the water column in the xylem breaks. When the soil is dry, the tree struggles to draw water up through its roots, releasing it out through its leaves. When the tree is unable to draw up enough water this creates a bubble in the water column, making a sound similar to when you slurp up the last of a drink through a straw.

TOUCH One of the most beautifully tactile plants in the Blue Mountains Botanic Garden’s collection is the prehistoriclooking Gunnera tinctoria. Located beside The Beach, the leaves of Gunnera tinctoria feel like rough, uneven sharkskin and are one of the most pleasing plants in the collection to touch. Often referred to as “dinosaur food” and native to southern Chile, Gunnera tinctoria grow up to 2.5 metres tall. A more diminutive member of the genus is endemic to Tasmania.

TASTE While eating anything growing in the Gardens isn’t encouraged (nor allowed), there are some magnificent edible, wild-collected native blooms that flower at the Blue Mountains Botanic Garden during the summer period. A good example is the Xanthorrhoea arborea in the World Heritage Garden, which was wild-collected from nearby Capertee and is abundant in the surrounding bushland. It has a beautiful honey, floral flavour when the nectar is sucked from the flowers.

Eucalyptus fastigata

Gunnera tinctoria Ferns can appear to glow in the early summer afternoons