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New Maps Available For Planners

Submitted By State Office Geotechnology Team

USDA Plant Hardiness Zones Map.

USDA Plant Hardiness Zones Map.

The State Office Geotechnology Team has developed two new maps for NRCS planners! The new maps cover Washington State and feature information related to Plant Hardiness Zones and Growing Degree Days. The maps can be found on the Washington State eFOTG under Section I/Maps. Hopefully you will find them useful!

USDA Plant Hardiness Zone Map

The Agricultural Research Service (ARS) released the new USDA Plant Hardiness Zone Map in January 2012. This new map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The zones are based on the average annual minimum winter temperature, divided into 10-degree Fahrenheit zones. This information is the culmination of an effort that was started more than 10 years ago. The work was done in conjunction with the ARS, but the actual climatology work was done by the NRCS National Water and Climate Center (NWCC) and Oregon State University (OSU). The PRISM group at OSU did all of the digital mapping. The new zones are based on climate data from 1976-2005, whereas the old non-digital map was computed using data from just 1974-1986.

For the first time, the information is also available online as an interactive GIS-based map, for which a broadband Internet connection is recommended. Users may simply type in a ZIP Code and find the hardiness zone for that area:

Washington Growing Degree Days Map

The Geotechnology Team worked with Leigh Nelson (State Irrigation Engineer, Ephrata) to develop a Growing Degree (GDs) Days map for Washington State. This map displays the degree-days greater than 5 degrees Centigrade, or 41 degrees Fahrenheit, based on mean monthly temperature.

Washington Growing Degree Days Map.

Washington Growing Degree Days Map.

GDs are defined as the number of temperature degrees above a certain threshold base temperature, which varies among crop species. The base temperature is that temperature below which plant growth is zero. GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature.
Growing Degree Units (GDUs) are accumulated by adding each day’s GDs contribution as the season progresses. GDUs can be used to: assess the suitability of a region for production of a particular crop; estimate the growth-stages of crops, weeds or even life stages of insects; predict maturity and cutting dates of forage crops; predict best timing of fertilizer or pesticide application; estimate the heat stress on crops; and plan spacing of planting dates to produce separate harvest dates.

The original digital data was downloaded from the Moscow Forestry Sciences Lab in Idaho. Additional information about Growing Degree Days can be found at their website:

These maps are just two examples of what is available out in the geospatial world. As you can see, there are many useful datasets out there and these can be very valuable for our planners and clients. If you have other map needs that we can help you with, please work through your area or state office specialists to contact us. We are here to assist the field.