Plant Hardiness Zone explained. This information is directed more at perennials (plants that continue to grow for many years).
Plant hardiness zones are mapped out to 5-degree increments in fahrenheit and are color-coded to show the different zones. You can find a color-coded map for every country. This map is representing the average annual minimum temperature for each zone within 5-degree increments. Click on the link at the bottom of the page to see the map I am using to explain the hardiness zones. The lower right-hand side of the map is the 5-degree color-coded increment chart, which is also numbered starting on the top with 1a being the coldest average at -60 to -55 degrees fahrenheit and -51.1 to -48.3 degrees celsius. On the bottom is 13b being the warmest average at 65 to 70 degrees fahrenheit and 18.3 to 21.1 degrees celsius. Match the color from where you live to the lower right-hand chart. The temperature on the left side is the average low in fahrenheit, and on the right side is the average low in celsius.
Now, you have found the average low temperature for your area. This information is important to know when you are deciding what plants you will grow. When you are deciding what perennials you want to grow over the years, you should look at the zones that they are hardy to. This means if you are living in zone 6a or 6b for example then you will want a plant that is hardy to zone 6 or lower, you do not want to get a plant that is hardy to zone 7 or higher. If you purchase online, the company should list that information within the description, if you are buying from a local plant nursery that should also be displayed on the tag. The local places should be selling plants that will be correct in your area, but if you don't see it displayed, I would be sure to ask about it.
Even though you have that information you may need to do more research for your specific area. There are also microclimates to analyze, which means if you live in a low-lying area it may be colder than what the hardiness zone graph is presenting for your area, there are also so many other factors due to the weather like how dry or wet your area may be, the sun, or shade in your yard. If your area receives more snow your plants will be insulated better from the cold weather throughout the winter months. You will need to take into consideration all these factors before you actually go out and get your plants. I hope you will take away knowledge from this, so you can better understand hardiness zones.
This is more directed to the annual plants. The information that you will want to know is the average frost date in your area, which you can type into google average frost date "your area," you can use this information for your annual plants with the average length of your growing season. The annual plants will have the days to maturity on the packet, that way, you will know if you will have enough time to grow that specific plant between the frost dates in your area. You can always get a bit of a jump start on the season if you are able to start your seedlings indoors, using this technique can allow you to get more varieties in your garden and may also allow you to get a second crop in for that season.
Click on the link below to see the hardiness zone map.