Margaret River's climate is categorised as 'West Coast Mediterranean' with its main feature being mild, wet winters and warm, dry summers. Average annual rainfall is 1190mm, although the total for December, January, and February averages only 48mm. Heat summation in degree-days is 1,597 compared with Bordeaux's rating of 1,463.
The very stable maritime climate of the Margaret River region with prevailing weather directly from the Indian Ocean provides local vineyards with an exceptional situation.
What should be emphasised is the special environment of the stretch of land from Cape to Cape. It suffers at times from intense southerly low-pressure systems, which can generate Equinoctial Spring Gales capable of damaging shoots and flowers. On the positive side, however, is the overall maritime system, which is very kind to vineyards. They are neither affected by frost nor extremes of summer and winter temperatures. Humidity levels are ideal during the growing period and the combination of climate, soil and viticulture practices leads to consistently high quality fruit of intense flavour.
The Leeuwin's Naturaliste Ridge rises from ancient granite land mass 2,000 million years old. Believed to have once been separated from the mainland, its soils are mostly formed from long periods of weathering in which granite decomposed to form iron-rich clay which precipitates to the surface, forming granite gravel loams which are ideal for grape growing. Due to their great age and constant leaching, these soils are relatively low in organic matter and essential elements, which is a feature favoured by winemakers while requiring their vineyard managers to carefully sustain necessary vine vigour.
Soils of the Margaret River GI region support towering Jarrah and Karri Forests, and others such as Marri, Peppermints, Black Butt and Blackboy. The best viticultural soils are generally regarded as those, which once supported Jarrah and Marri. Forests in their natural state give the message that this is a different and special environment found nowhere else in the world, while the clean white beaches and limestone outcrops that are lapped by the bright blue Indian Ocean enhance the fresh, clean, natural image.
The region is strongly maritime influenced, being surrounded by ocean on three sides – virtually unique in Australian wine regions.
It has a low mean annual temperature range and in terms of rainfall, a Mediterranean climate with a low annual rainfall between October and April. It is very similar in climate to Pomerol and St Emillion in Bordeaux, in a dry vintage. Therefore, it’s little wonder the cabernet sauvignon is so damn good!