Today’s USDA Plant Hardiness Zone Map and How to Use It

plant_hardiness_zone_mapBefore you plant the first seed in your flat or plan your garden, you will need to check the USDA Plant Hardiness Zone Map.  This is a crucial step that many gardeners skip because they do not know how to use the map or do not understand the information on the map.

Past USDA Plant Hardiness Zone Maps have been divided into 10 categories.  These categories were separated by 10 degrees.  This 10-degree margin represents the average minimum winter temperature of an area.    These margins are then divided into areas labeled “a and b.”  These areas are separated by 5 degrees and add more climatic detail to a region.

All this information is compiled by weather stations scattered throughout the country.

In 2012, a new map was released.  The temperatures that were used to create this spanned a time period that went from 1976 through 2005.  The information compiled indicated that two additional zones needed to be added.  In doing so, the 2012 version of the USDA Plant Hardiness Zone Map now consists of 13 zones.  These zones are again broken down into “a and b “ sections.

Not only are there more zones in this new map but also for the first time, the government will not print the map.  Individuals can though, print their own copies.  Another difference is the fact that all the gardener’s guesswork is taken out.  You no longer have to guess where your area is in a state, but instead you just need to know your zip code.  This allows a more accurate determination as to where ones garden is located.  To find the 2012 USDA plant Hardiness Zone Map visit their online map.

When utilizing the map there are a few rules to follow.  First, if you are a beginning gardener it is a good idea to follow the map precisely.  While this winter may be unusually warm and you think you can use something in a different zone, do not.  It never fails that sometime in an area’s history, the winter goes beyond its norm and in doing so all the plant material that is not designed for that zone will die.

Second, if a range of zones is listed in a plant description follow this to a tee.

If you are a more experienced gardener, then you can deviate a little from the map but be careful.  Things such as living in an urban or inner city environment can affect your area along with the amount of hardscape in the landscape.  Both of these factors can create a heat island, which can skew the region’s temperatures.  In other words, these environments are typically warmer than the average recorded temperature of the region.  In doing so, you can experiment going into another temperature zone, but always be aware of the possibility of a freaky cold snap going through your area.

If you decide to use this approach never move up more then one zone unless indicated by plant requirements.

Today’s USDA Plant Hardiness Zone Map provides the most accurate information one can use to plan their garden space.  But keep in mind that this is just one piece of the planning puzzle that helps a beginning gardener find success or a successful gardener become more productive.

Mindy McIntosh-Shetter has been an Agricultural Science educator, and is a horticulture and/or environmental blogger who earned a degree from Purdue University in Agriculture Education with a minor in biology, and natural resources. Presently she is finishing up her Masters in Environmental Education and Urban Planning for the University of Louisville while working on her own agriculture/environmental blog.

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