Which USDA Hardiness Zones Correspond to the Australian Climate Zones – Permaculture

Can we convert USDA zones to Australian climatic zones of tropical, subtropical, temperate, arid and funky/alpine areas?

That’s a typical query many gardeners ask when referencing plant data from the opposite facet on the world.

Although the 2 are fairly completely different measurements based mostly on moderately completely different standards, we are able to roughly approximate them for sensible functions.

The USDA Hardiness Zones

The idea of USDA Hardiness Zones was developed by the US Division of Agriculture based mostly on the common annual excessive minimal temperatures recorded over a interval of the previous 30 years.

It’s vital to notice that this measurement just isn’t referring to the common minimal temperature throughout the entire yr, which is a distinct idea.

USDA Hardiness Zones are divided into 13 separate planting zones, with every rising zone being 10 °F colder or hotter than the one earlier than or after it. Moreover, every of those rising zones is additional divided into an ‘a’ and ‘b’ zone with a 5 °F temperature distinction between them, as proven under:

USDA Zone Minimal Temperature Ranges

Zone: Common Annual Excessive Minimal Temperature Vary

1a: -60 to -55 °F (-51.1 to -48.3 °C)
1b: -55 to -50 °F (-48.3 to -45.6 °C)
2a: -50 to -45 °F (-45.6 to -42.8 °C)
2b: -45 to -40 °F (-42.8 to -40 °C)
3a: -40 to -35 °F (-40 to -37.2 °C)
3b: -35 to -30 °F (-37.2 to -34.4 °C)
4a: -30 to -25 °F (-34.4 to -31.7 °C)
4b: -25 to -20 °F (-31.7 to -28.9 °C)
5a: -20 to -15 °F (-28.9 to -26.1 °C)
5b: -15 to -10 °F (-26.1 to -23.3 °C)
6a: -10 to -5 °F (-23.3 to -20.6 °C)
6b: -5 to 0 °F (-20.6 to -17.8 °C)
7a: 0 to five °F (-17.8 to -15 °C)
7b: 5 to 10 °F (-15 to -12.2 °C)
8a: 10 to fifteen °F (-12.2 to -9.4 °C)
8b: 15 to twenty °F (-9.4 to -6.7 °C)
9a: 20 to 25 °F (-6.7 to -3.9 °C)
9b: 25 to 30 °F (-3.9 to -1.1 °C)
10a: 30 to 35 °F (-1.1 to 1.7 °C)
10b: 35 to 40 °F (1.7 to 4.4 °C)
11a: 40 to 45 °F (4.4 to 7.2 °C)
11b: 45 to 50 °F (7.2 to 10 °C)
12a: 50 to 55 °F (10 to 12.8 °C)
12b: 55 to 60 °F (12.8 to fifteen.6 °C)
13a: 60 to 65 °F (15.6 to 18.3 °C)
13b: 65 to 70 °F (18.3 to 21.1 °C)

The best way this USDA scale is used, if a plant is described as being “hardy to zone 10” which means the plant can face up to a minimal temperature of 30 °F (−1.1 °C) the bottom temperature of Zone 10a by to 40 °F (4.4 °C) which is the higher restrict of Zone 10b.

The idea of USDA Hardiness Zones has a number of limitations we’d like to pay attention to. Since this mannequin relies on the coldest temperatures skilled, it doesn’t incorporate warmth ranges throughout summer season when figuring out the zone score. Because of this two areas with the identical minimal winter temperatures however with completely different summer season temperature could be assigned to the identical hardiness zone.

The Australian local weather zones bear in mind numerous components resembling temperature, rainfall, humidity, elevation, and particular regional situations, so that they don’t have a direct one-to-one correspondence with the USDA Hardiness Zones.

We will nonetheless roughly align the USDA Hardiness Zones with the Australian climatic zones as detailed under:

Tropical Zone:

USDA Zones: Usually, USDA Zones 10-11

Clarification: The tropical zone corresponds to areas with constantly heat temperatures year-round. Within the USDA system, Zones 10 and 11 cowl areas with comparatively delicate winters and excessive temperatures, which will be much like tropical situations.

Subtropical Zone:

USDA Zones: USDA Zones 9-10

Rationale: The subtropical zone has heat to sizzling summers and delicate winters. USDA Zones 9 and 10 embody areas with comparatively delicate winters and are thus much like subtropical climates.

Temperate Zone:

USDA Zones: USDA Zones 4-8

Rationale: The temperate zone encompasses a spread of climates with distinct seasons. USDA Zones 4-8 cowl a wide range of climates with chilly to delicate winters and heat to sizzling summers, which may align with temperate situations.

Arid Zone:

USDA Zones: USDA Zones 8-11 (for areas with desert-like situations)

Rationale: The arid zone corresponds to dry and desert-like climates. USDA Zones 8-11 can embody areas with low rainfall and excessive temperatures, that are attribute of arid areas.

Cool/Alpine Zone:

USDA Zones: USDA Zones 1-6 (larger elevations)

Rationale: The cool/alpine zone corresponds to areas with colder temperatures, usually discovered at larger elevations. USDA Zones 1-6 embody areas with chilly winters and shorter rising seasons, which align with cool and alpine situations.

We have to take into account that whereas these normal correlations present a tough approximation of USDA zones with Australian local weather zones, they aren’t exact matches, so it’s finest to verify the rising necessities of any crops and their suitability to your location earlier than planting.

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Angelo Eliades is a presenter, coach, author, permaculture guide, city permaculture pioneer and meals forest specialist.
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