Frost-Hardiness-Planting Zones And Growing Season


Your growing season is basically figured by your climate, coupled with the type of plant crops you choose to grow. Growing season factors include your geographical location, elevation, temperatures, daylight hours, and rainfall.

The growing season is often summarized as the days between first and last frost. In the northern United States, this is roughly April-May to October. In the milder regions it is roughly February/March to November or longer.

Here are two tools to help determine the finer details of your growing season.


Planting Zones

The USDA Agricultural Research Service has updated their Hardiness Zones Map for the U.S.

They revised it during 2012, and it is now more specific with finer resolution and specific and interactive information with granularity to your local region.

The Plant Hardiness Zone Map can be used as a tool to determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 5-degree F zones.

The planting zones are calculated based on the average annual extreme minimum temperature.


Plant Hardiness Zones Map KEY


While looking at the map ‘key’, you can see how the zone numbers are scaled to finer detail with the alpha subsets (e.g. 6a, 6b, 7a, 7b, etc.). The temperature (degrees-F) represent the extreme minimums for that given zone – kind of a worst-case scenario.

The online hardiness (planting) zone map enables you to select State, Regional, or National views, in various resolutions. You can view, download and save, and even print the maps.

For even finer resolution, use the interactive hardiness (planting) zone map which enables you to zoom in right to your town – providing an additional level of granularity of local variations. By clicking on any point within the map you will be presented with more information about that area – the specific average (extreme) cold temperature, latitude-longitude, etc.)

About the new planting zone map:

Because this map was created digitally with GIS technology (geographic information system), it has a higher level of resolution and can show smaller areas of zone delineations than ever before. For example, cities tend to hold more heat because they have large amounts of concrete and blacktop, so a city or town may be assigned to a zone warmer than the surrounding countryside. Higher elevations tend to be colder than surrounding lower areas, so the top of a mountain may be an area of cooler zones. A location near a large body of unfrozen water may provide milder winter weather and be in a warmer zone.


First and Last Frost Date

Your planting zone is a good guide, but more information is better. Knowing the fist and last frost date for your region will help you narrow down the time of your growing season.

Using the online frost-dates calculator from the Old Farmer’s ALMANAC, it’s easy to find your last frost date for the spring and first frost date for the fall for the United States. Just enter your zip code (or city, state). The results will also include the number of growing days available (based on average frost dates).

In conclusion, first determine the plant hardiness zone where you live, and then the first and last frost dates. This will enable you to determine your growing season days and better choose vegetable varieties that are best for your area.


A few crop suggestions based on your time of Spring:

Very Early Spring


Early Spring


After Last Frost Date


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