Seasonal Changes

I've been noticing as probably many others some signs of seasonal change of late. The  annual weeds growing up through the cracks in the cermet are beginning to flower, the lemon tree out the back has started to produce new growth, I began to wonder just how plants are able to tell when it's time to flower and produce seeds. This strategy would be crucial to it's survival and chances of reproduction. This timing is also needed to be know by food growers to ensure successful harvest.
When the French explorer Samuel de champlain arrived in Cape Cod in 1605, the Wampanoag people informed him the best time to plant corn was when the white Oak leaf was the same size as the foot print of a the Red squirrel.
Australian Aborigines recognised roughly 6 seasons one being;
Rarrandharr – the main dry season. "The warm south east wind blows as the pandanus fruit begins to fall to the ground. As soon as the stringybark tree flowers, snakes lay their eggs and all types of honey can be found.
A good method for a gardener to know when it's time to plant summer crops like tomato and capsicum.
Once the pumkin seeds in your compost start to germinate you know the soil is warm enough to start planting summer crops.
Plants recognizes the decreasing length of darkness and increasing length of daylight which signals a chemical feed back loop that springs the plant into action or in the case of a coming winter deaction.
The distribution of plants over the globe is closely related to the day/night length of the region.
Spinach and lettuce for example will grow in a tropical winter, however it would be difficult of the plant to produce viable seed as the days in the tropics are never long enough to stimulate the flowering process.These types of plants are know as obligate.
Tomatoes are known to be day neutral, they use only temperature as a guide as to when to flower. these types of plants are known as faculative.
There is however a problem with using the day/night length alone to determine when to flower. Flowering too early, then having a late frost could spell disaster for the plant. Plants have evolved a number of different ways to overcome the problem. Some plants like mangoes will only flowers after going through a prolonged period of cold. This will have major implications for growers as the climate warms - the warmers summers may not be as much of a problem, however warmer winters will see the viability of some agricultural industries in some areas finish and some native plants will become extinct.

The seasons in the Southern Hemisphere are:

•Summer: December, January and February   December 21 Longest day of the year 

•Autumn: March, April and May

•Winter: June, July and August                       June 21 Shortest day of the year

•Spring: September, October and November
 

Date     Jan 1     Jan 16     Feb 1     Feb 16     Mar 1     Mar 16


Hours   14.79     14.54      14.08        13.52      12.98       12.32
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Date     Apr 1     Apr 16    May 1      May 16   Jun 1       Jun 16

Hours  11.59      10.93      10.32        9.79        9.37         9.18
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Date     Jul 1     Jul 16      Aug 1      Aug 16    Sep 1     Sep 16

Hours   9.19       9.42        9.87         10.41     11.08      11.75
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Date    1 Oct     16 Oct     1 Nov   16 Nov    1 Dec    6 Dec

Hours  12.42      13.08       13.73     14.25      14.63   14.83
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