Occasionally, I receive e-mails from readers who are confused about which gardening or climate zone they live in. Australia has been divided into as many as eight different gardening zones because of the huge variations in temperature and rainfall across our continent. Altitude variations or geographical features within each zone will modify temperatures and rainfall patterns, breaking up the eight zones even further.
To complicate the issue, climate change is resulting in evolving milder winter conditions in some areas and longer, harsher winters in others. Last summer, extreme heat or rain events played havoc with a lot of gardens across Australia, and the extent of further changes related to extreme weather events is impossible for anyone to accurately predict.
However, Australia can be divided into three basic gardening or growing zones; Warm, Cool, and Temperate (as indicated in the diagram below). The zone divisions are based on the types of plants that will grow in a moderately irrigated garden in each zone
Within these basic zones, altitudes and geographical features gardens at higher altitudes will be cooler than those at sea level in adjoining areas. Sea breezes can provide a milder climate for coastal areas than those a few kilometres inland. Gardens where cold air can flow downwards will be less damaged by frost than gardens in valleys or where solid walls block the escape of cold air. These variations are known as local microclimates, and gardeners may have to make minor adjustments to what they can grow each month according to local conditions, and evolving microclimates brought about by climate change.
New Zealand has a more constant climate and can be divided into temperate and cool zones. Frosts do occur, and snow falls on the mountains, but New Zealand is not subject to hot winds from a parched inland. New Zealand is a very suitable place for growing an extensive range of species from Europe, North America, and the cooler parts of Asia.
WARM CLIMATE ZONES
These are frost free, or may experience some frosts in inland areas during their short winters, and are not suitable for plants that require a defined period of chilling. Warm zones are suited to warmth-loving Australian natives and plants, including fruits and vegetables, from warmer areas of the world. December, January, and February can be too hot for gardening in a lot of warm zones, and some warm zones experience distinct wet and dry periods requiring conventional vegetables and some annuals to be grown at different times to other zones.
The Tropic of Capricorn runs through the northern states of Australia from Rockhampton and Longreach in Queensland, just above Alice Springs in the Northern Territory, and crosses the West Australia coast between Carnarvon and Exmouth. In areas from Rockhampton northwards, tropical coastal conditions allow an entirely different style of gardening, while in drier areas high temperatures and lower water availability make gardening quite a challenge. Winter temperatures in areas within the Tropic of Capricorn can be higher than summer temperatures in some Cool Zones, and common vegetables from temperate areas can only be grown during winter months. Consequently, I have divided this zone into two sub-sections.
All of Queensland (except for the southern highlands),
North coast of NSW above Coffs Harbour,
Northern West Australia,
Northern South Australia.
COOL CLIMATE ZONES
These are areas where low temperatures occur for long periods. Frosts are common in winter and can continue into spring. Snow occurs in some areas. Cool zones are suitable areas for growing many European, Asian, and North American plants that require a period of winter chilling. Many of the fruits and vegetables we are familiar with come from cooler climates. They, and frost-hardy Australian natives, grow well in Australian cool zones, but frost-tender plants, and plants which require a long period of warmth to flower or fruit are unsuitable for these areas.
Australian cool zones:
All of Tasmania, and the ACT,
Southernmost part of South Australia including Mt Gambier,
Around Albany in Western Australia,
Most of Victoria (except for Melbourne and Benalla areas),
Far south coast of NSW,
NSW tablelands and highlands.
New Zealand cool zones:
The interior of the North Island,
The entire South Island.
(However, within these areas, protected local microclimates along the coast as far south as Christchurch can be regarded as cool temperate areas, extending the planting range.)
TEMPERATE CLIMATE ZONES
These, strictly speaking, are all areas on earth between the Polar Regions and the Tropics of Cancer and Capricorn. Although winter frosts occur in some temperate zones, soil warms quickly in spring. The areas of Australia not listed above can be considered temperate zones, because an extensive range of Australian and New Zealand natives, and decorative plants, vegetables, and fruits from temperate regions around the world can be grown in these areas. January to late February can be too hot for a lot of gardening activity in some Australian temperate zones, but mild autumn weather usually extends from March through May.
Minimum temperatures within metropolitan areas of Sydney, Adelaide and Perth are similar and tend to be slightly higher than those in surrounding areas. Melbourne’s minimum temperature is only slightly lower, and gardeners in Melbourne may find that they can grow many temperate climate plants in protected gardens.
On the North Island of New Zealand, North and South Auckland areas, Hamilton, most of the west coast to just above Wellington, the Bay of Plenty area, and the east coast to Hastings are temperate zones.