Hardiness Zones | garden hardiness

US plant hardiness zones and its significance and drawbacks

Plant hardiness zone or garden hardiness zone is an area in which a particular variety of plants are able to grow and endure the climatic condition of that particular zone  and have  been able to survive in the minimum temperature of that zone.

Actually Vertical Zone sub-categorized into plant hardiness zone. United states Department of agriculture first introduced the map of plant hardiness zone. Consequently, other countries adopt this feature. As an example, if a plant can endure to zone 10, it means that the plant can survive at a minimum temperature of -1°C.

Importance of plant hardiness zone

Few issues should be taken into consideration prior to growing your own vegetable garden or buying seeds for your garden. You need to know under which USDA hardiness zone your living area falls, the AHS Plant Heat Zone of your area, and your microclimate.

The United States Department of Agriculture divided the area of US with a zone hardiness map as a common guideline to help cultivator to grow suitable crops that can withstand the extreme climate of that particular area. However, it is essential to know that no map is able to presume about particular microclimate that can influence a city, zone even yard.

Actually, the USDA hardiness zone map works best when we consider growing perennial plants. This is due to the fact that any yearly plants would be able to grow in any hardiness zone as long as it experienced sufficient warm days to reach harvest. This is one utmost factor for gardeners or cultivators to find out the days of a particular plant to reach harvest or at least know a rough count, before buying seeds of that particular variety of plant.

For an example if you find a plant that needs 100 warm days to reach harvest, and if you grow same plant in another area, which receives on average 120 warm days or more annually, it would survive. But, if you want to grow same plant in the zone which experiences only 60 days of warmth, then you should look for a variety which would be harvested in a shorter period.

US plant hardiness zone map and how to use it
To locate a specific zone on the plant hardiness map, one must be required to acknowledge themselves with the minimum temperature of that particular zone experiences. If you are not aware of the fact, then you can consult your local Cooperative Extension office or weather station. They will help you to find out the zone. If the minimum temperature of that particular zone swings between 20°F to 30°F, then that particular area falls under zone 8; if the area you live experience minimum temperature of 40°F  but, above 30 °F then you live in zone 3. Consequently, if the temperatures of a particular plunge down as low as 50°F  or 60 °F degrees, its indicates the gardener belongs to Hawaii or anywhere similar climatic zone which falls under zone 11.

There are 11 plant hardiness zones in  theUSA. The 1990 version of US plant hardiness zone map provides the detail picture of these zones and the annual minimum temperature experienced by the country. Defined as “average annual minimum temperatures”, these temperatures are calculated on the basis of minimum temperatures experienced by the United States and Canada between the year 1974 to 1986 and for the Mexico it is 1971 to 1984. The earlier map reveals 10 hardiness zones. Each zone specifies an area of winter hardiness for the agriculture crops and plants. Later a new zone i.e., zone 11 has been introduced to specify the area which faces the minimum temperature more than 40°F and this zone is definitely frost free.

The 11 plant hardiness zones

1. The area which experiences less than -50°F annual minimum temperature falls under zone 11.
2. Zone 2 experiences annual minimum temperature between -50°F to -40°F
3. The area which receives annual lowest temperature between -40°F to -30°F represents zone 3.
4. zone 4 represents the area which receives annual minimum temperature of -30°F-20°F
5. The area where the temperature plunges down to -20°F to -10°F specify zone 5.
6. If you live in the area where temperature drops down to -10°F to -0°F then your zone falls under zone 6.
7. Zone 7 represents the area where annual minimum temperature falls to 0°F- 10°F.
8. In similar way Zone 8 represents the area which faces annual minimum temperature of 10°F to 20°F
9. Zone 9 represents the area where annual minimum temperature falls to 20°F to 30°F
10. similarly zone 10 experiences minimum temperature if 30°F- 40°F
11. Zone 11 receives annual minimum temperature of 40°F- 50°F
    

Drawbacks of the US plant hardiness zone map.

Though the plant hardiness zone map is a great help for gardeners but, it has several drawbacks.  If we are using it without taking into consideration of other factors like microclimate of that particular area, pollution and man-made artificial climate which resulted due to modernization of human civilization.

The most important drawback, it does not include summer heat levels while specifying the zone; therefore, the area which has the same annual minimum temperature, but  summer temperatures varies greatly, falls under the same hardiness zone.

Another drawback of the hardiness zones is that it didn’t include the snowfall of particular zone. Snow works like an insulator during severe cold, shielding the root system of hibernating crops. If the snowfall of a particular zone is optimum, and generally exist round the winter season, then the actual temperature the roots receive will not be as low as specify by the hardiness zone

Apart from this type of soil, moisture, frost day are also important for growing plants, which is not considered while mapping plant hardiness zone

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