Light Spectrum  How light is shade

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Dr David Bromwich is a retired occupational hygienist who dabbles with gardening.


Shade can vary from deep shade, lacking any direct sunlight or light from the sky, to harsh direct sunlight from a clear sky. There is a difference in what a person sees and what a plant needs.

What we measure with a Lux (light) meter or camera exposure meter is the response of the eye to the visible spectrum. While our eyes are most sensitive to green light, plants are largely blind to green light and reflect it. Plants need light in the blue and red ends of the spectrum for photosynthesis.

The sky is blue due to a (Rayleigh) scattering of about 25% of the sun’s light by air molecules in the atmosphere. More blue light is scattered than other colours, so the sky appears a deeper blue on a clear day.

The sensitivity of our eyes to the different wavelengths of light is documented as the CIE (International Commission on Illumination or Commission Internationale de l’éclairage) Photopic Curve. For plants, this is approximated by a PAR (Photosynthetically Available Radiation) curve.


From a 2 page Feature Article in Issue Thirty Six
Supporting Graph
Supporting Graph
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Garden Calendar

Paul Plant

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The period from winter, spring and into summer here in the tropical and subtropical zones of Australia is typically characterised by clear skies, low rainfall, low humidity and bushfires. Weather however does not always do as it is expected – rain will sometimes occur out of season and with it comes cloudy days.

Rain during this period means bushland species and ornamental gardens burst into growth and flower, making it a great time to do bushwalking, visit a botanic garden, an open garden or just visit a friend’s garden.

Bushwalks are one of the best ways to see how nature has adapted to the local climate, soil and conditions. Many native plants, such as king orchids, come into bloom during this late winter-early spring period. Nature inspires
the best professional horticulturists and also inspires gardeners.

Seasonal annuals if planted in past months are now in full bloom and will need regular watering, feeding and deadheading of spent blooms. All this extra work means the annuals will keep on flowering over many more weeks and months.

Information is given for what to do in each of the months:

  • August
  • September
  • October
  • November

Special information is also provided for:

  • Vegetable planting schedule for August, September, October and November for subtropics and tropics.
  • Annual planting schedule for August through November.

The full Vegetables and Annuals Planting Schedule for these months is also available.


From a 5 page Feature Article in Issue Thirty Six
Visit a Botanic Garden to see what the plant kingdom is doing at this time of year.
Hibiscus Harlequin Bug (Tectocoris diophthalmus) should be controlled once they are sighted.
Chickens can cause serious damage to a vegetable garden. If chickens are to free range, you may need to fence off the vegetable garden.
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