Plant Hardiness Zones

There are several different plant hardiness zone descriptions (also known as growing zones or climate zones). The version many gardeners are familiar with is the USDA Hardiness Zone Maps. This map is broken into 11 temperature zones as follows:

USDA Plant Hardiness Zone Map

Zone 11: (above 40 F) or (above 4 C)

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Sunset Zones (Problems in the West versus East)

In the United States there is another set of measurements that were created for the Western States called The Sunset Zone Maps. These are based on a 24 climate zone system created by Sunset Magazine, and are more precise for those regions than the USDA zones maps. They take into account:

• Winter Minimum Temperatures
• Summers High Temperatures
• Length of Growing Season
• Humidity Levels
• Rainfall Patterns.

The West has different circumstances that affect plant growth. Elevation and precipitation from weather coming in off the Pacific Ocean becomes gradually direr as it moves over mountain range after mountain range. Cities in the Eastern US can be in the same zones and have very similar growing conditions with weather. On the other hand, cities in the West can be in the same USDA zones but have a very different set of conditions for growing

In the Western United States you’ll find garden centers referring to the Sunset Zones more often than the USDA Zones. The reason USDA Zones are still important nationwide in the USA is that it’s the standard large growers use in general when selling seeds and flowers.

Micro-Environments:

Within every climate zone there are small weather environments unique to the area. Even in your own back yard there can be multiple “micro-environments” depending on:

• Shade or Sun
• Soil Drainage (wet all the time or dry)
• Soil Types & Condition (hard, composted, or others)
• Shelter from the wind
• Access to water or rain.

In addition to natural “micro-climates” you can artificially create these by planting shade trees, putting in large rocks, adding a garden pond, and many other gardening actions to alter your area.

The really neat thing about this is you can have plants and flowers from different hardiness zones growing in your garden at the same time.

Examples of climate growing zones from around the world are:

America’s:

• USDA Hardiness Zone Map (just USA)
• North American USDA Plant Hardiness Zone Map
• Canada Plant Hardiness Zone Map
• South America Hardiness Zone Map

Australia:

• Australian Government Climate Map
• Plant Hardiness Zones for Australia

Europe:

• Europe Climate Zone Map
• Hardiness Zone Map for Europe
• Europa Hardiness Zone Map (shows East of Moscow)

Plant hardiness zone maps are great in general for determining which plants you can grow in the region you live. There are some disadvantages to this method of mapping. The USDA Hardiness Zoning only takes the average minimum temperatures a region will encounter to come up with their mapping.

Why is this an issue? There are several factors beyond pure temperatures that go into whether a plant or flower will grow and thrive in a particular region. Other important things in addition to temperature affecting plant growth are:

• Heat
• Rainfall
• Frost
• Sunlight & length of day
• Altitude
• Soil Types (including pH levels)
• Day time temperatures
• Micro-environments
• Others…

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• Precipitation
• Air Temperature

The sun’s rays hit the equator at more direct angles than the rest of the world and thus give more warmth and direct lighting to plants. Our world-wide climate is affected by the location of hot and cold air-mass regions as well as by the trade winds and westerlies that carry it.

Trade winds South of the equator blow from the Southwest and North of the equator blow from the Northeast. These trade winds meet near the equator, causing air to rise and form clouds and rain. This of course is the reason for tropical wet conditions closer to the equator.

Westerly winds direct weather patterns of rain from West to East across middle latitudes. You end up with tropical deserts as well because of wind patterns. The tropical deserts such as Sahara (Africa) and Sonoran (Mexico) are results of intense heat evaporating moisture before it develops into rain.

Seasons:

All of the wind patterns, which lead to rain patterns as well, are also affected by the Earth’s rotation about its axis. Because of this continual rotation the sun is hitting the earth at different angles and various intensities all year long (This creates Seasons). Some areas get more extreme weather fluctuations than others because the sun is coming in at different angles.

MOST WIDELY USED WORLDWIDE CLIMATE SYSTEM

Koppen Climate System

The Koppen Climate Classification System is very detailed and the most accurate on a world-wide basis. It has 5 major climate types and several sub-categories of those.

1- Moist Tropical Climates – These are known for their high temperatures year round as well as large amount of year round rainfall.

2- Dry Climates – These are climates that are characterized by little rainfall and a large daily temperature range. Within this there are (1) Semiarid and (2) Desert or Arid.

3- Humid Middle Latitude Climates – In these climates land and water relationship differences play a big role. These climates have warm & dry summers, and cool & wet winters.

4- Continental Climates – These climates are found in the interior regions of large land masses. In these total precipitation is not very high and seasonal temperatures vary widely.

5- Cold Climates – These climates are cold with areas where permanent ice and tundra are always present. These climates usually only have about 4 months of above freezing temperatures in the year.