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In the United States, two types of zones are most commonly used when determining the right plant for the right area. Up until fairly recently, the Plant Hardiness Zone Map was the most referred to tool for plant selection.

 

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The Plant Hardiness Zones were developed by the United States Department of Agriculture (USDA) and have been in use since 1960. These zone maps provide information on minimum temperatures across the country in various geographical regions. Basically the zones indicate which plants grow well in which area of the country. There are eleven zones and their categorization is determined by whether they are ten degrees Fahrenheit warmer or colder that the adjoining zone. If your area has a low Zone number it is a colder climate than those areas with a higher Zone number. These temperatures are determined by measuring climate in an average winter period for each area.

So how does the information from the Hardiness Zone Map help you? Well, when selecting a plant you want to survive for a significant period, you will need to investigate what the annual temperatures are for your area. The Zone map can be found on most seed packets so knowing your Hardiness Zone will help determine if the plant you have chosen is suited to where you live and the expected climate of that area.

However, the Hardiness Zone has been found to have some short-comings, especially for states in the west. Growing climates differ significantly in same numbered zones so more information was needed to correctly determine the type of plants that will grow in specific areas, therefore the Heat-Zone map was developed.

Across the country, from 1974 to 1995, weather stations recorded their maximum daily temperatures. Each participating weather station had to provide information for a twelve year period at least, to be included in the data. The American Horticultural Society (AHS) then used this information to develop the Heat-Zone Map which was released in 1997. There are twelve zones in this map and they are categorized by the number of days that area is subjected to temperatures above 86 degrees Fahrenheit, (also known as ‘heat days’). This temperature was chosen because 86 degrees is when plants begin to experience damage from heat. The lower the Zone number, the lower the amount of heat days experienced. For example, Alaska falls in Zone 1 which means it has less than one heat day per year. Zone 12 experiences a significant period of the year in heat days – more than 210 of them!

So now plants are coded for their ability to withstand heat and their hardiness. Each coded plant will have four numbers which relate to their heat and hardiness zone relativity. These numbers will give you a good indication if the plant you want is suitable for the area you live in. Always remember that the coding is reliant on the plant getting sufficient water. If the plant is affected by dry conditions they may not thrive as well as expected. You will also need to ensure your plants have adequate oxygen, light and air movement. Again, their tolerance to heat may not be as expected if these are not managed sufficiently. And don’t forget your soil pH! If you want your plants to thrive as suggested by the heat and hardiness zone maps, you must take care of these variables.

So now you need to find out what zone, for heat and hardiness, you live in. Once you know this information you can begin to select the right plants for your garden.

We hope you enjoyed this third of 5 episodes dealing with Sucessful Gardening All Year Long, and that it provided you with ideas you hadn’t thought of for your gardening all year round.

For much more information about Successful Gardening All Year, please visit our site at:

http://gardening.howto-you.com , where you will find an additional email list of ideas, as well as our book ‘Guide to Successfull Gardening All Year’

Thanx for being here!  See you in our next episode!