By Jez Clark
Cast your mind back to school science lessons and a process called photosynthesis.
Plants take in light and carbon dioxide via their leaves, then through their roots they take up water helping them to convert that light energy into sugars, enzymes, and chlorophyll that they use to grow.
The range of light intensity for optimum photosynthesis for a plant usually relates to the microclimate in which it evolved.
Plants from prairies or deserts function and flower best in full sun, plants of the forest floor suiting shade. The origins of a plant will help us to determine where to plant it.
For example, the Tractor Seat Plant (Ligularia reniformis) comes from the damp woodlands of East Asia and should be planted in shade.
Westringia fruticosa from the coastal margins of New South Wales, requires full sun.
The Ligularia has large green leaves maximising access to limited light.
The Salvia has small grey leaves; it is more concerned with sunburn and water loss than maximising light for photosynthesis.
If plants are exposed to light levels beyond their level of tolerance cells are damaged and “burnt” by high levels of ultraviolet light.
If they have too little light, they become ‘leggy’ in a process called etiolation.
When we read plant labels, they will refer to sunlight definitions which indicate the minimum hours of direct, unobstructed sunlight a plant requires to thrive.
These definitions are based on the number of direct sun hours an area receives.
Full Sun requires six or more hours of direct sunlight, Part Sun/Shade three to six hours, and Full Shade means less than three to four hours or only dappled light.
Another consideration with sunlight is direction.
North-facing receives the most sun, ideal for sunny, and warmth-loving plants.
South-facing receives less sun, is generally cooler and shadier; best for shade-loving plants or ferns.
East-facing gets morning sun and afternoon shade, good for plants that dislike extreme heat such as hydrangeas.
West-facing gets the hot afternoon sun, and is best suited to tough, heat tolerant plants.
Next week I will focus on the impact of heat on the garden and the rising summer temperatures we have been experiencing.
Visit Clark+Granger at www.cplusg.com.au or phone 0456 111 120 to find out more.
