USDA Plant Hardiness Zone Map
Image source: https://planthardiness.ars.usda.gov/
Interpreting the Plant Hardiness Zone Map
Updated: 11/17/23 by Jonathan Foster, Horticulture Outreach Professional
How does this Hardiness Zone Map differ from the old one?
- The new map is based on about 30 years of weather data, from 1991-2020, and the recommendations from a multi-disciplinary panel of experts. This recent data is also being used by climatologists in the field.
- Maine’s temperatures now appear slightly warmer. Part of this “warming” may be a result of higher resolution due to the use of GIS techniques in the new map.
What do the Hardiness Zones mean?
- Maine spans Plant Hardiness Zones 3-6. Each zone is based on the 30-year average of the single coldest temperature recorded each winter. Zone 3 is 10 degrees F colder than Zone 4, etc. In addition, each zone is split in half. For example, sites in Zone 4a reach an average low temperature of -30 to -25 F, while sites in Zone 4b reach an average winter low temperature of -25 to -20 F.
What do the Hardiness Zones NOT mean?
- The map is a guideline, not a guarantee. A plant rated hardy to Zone 4b would likely thrive in Zone 5a, do well on good sites in Zone 4b, and might survive in quite protected sites in Zone 4a.
- The map does not consider other factors that affect plant survival: summer temperatures and heat accumulation, length of growing season, depth of snow in winter, exposure to wind, soil drainage, soil fertility, quality of plant specimens, and management practices.
- The map is more accurate for trees and shrubs than for herbaceous perennials like iris and poppy, because snow cover greatly affects the winter survival of herbaceous perennials. An herbaceous perennial in a cold location with deep, reliable snow cover may survive better than one in a warmer zone where the ground is exposed to winter air.
How can you best use the map to select landscape plants?
- The source map (https://planthardiness.ars.usda.gov/) offers a new personal zip code finder. Simply type in your zip code to determine your cold hardiness zone.
- Be conservative when trying new plants. To be more certain about a new plant, buy a species rated one-half or even one full zone colder than the site is rated.
- Buy the best quality plant available. Follow good planting practices–water well during the establishment period (this can be several years), fertilize as recommended, scout for problems and resolve them promptly–and reach out to the UMaine Cooperative Extension before purchase or planting with any questions you may have regarding siting and proper care of the prospective plants.
From the GardenPro Answer Book; revised and updated by Lois Berg Stack, Ornamental Horticulture Specialist, University of Maine Cooperative Extension.
FAQs
MAINE. Most of Maine is considered zones 4b, 5a, and 5b, although there are some area along the Midcoast and islands that touch 6a. The majority of Knox, Waldo, Lincoln and Hanco*ck Counties are considered 5b.
Why is the USDA plant hardiness map helpful? ›
The USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location. The map is based on the average annual extreme minimum winter temperature, displayed as 10-degree F zones and 5-degree F half zones.
Is Maine zone 5? ›
Most of Maine is in zones 3-5. Find your zone here.
Is zone 4 colder than 5? ›
If I lived in zone 4, then the plant will not be perennial for me, since zone 4 is colder than zone 5. If your zone is lower than the zone listed on the tag then the plant will not be hardy for you, it is an annual in your area.
What is the highest hardiness zone? ›
The hardiness zones defined by the USDA begin with zone 1, which is the coldest and end with zone 13, which encompasses the warmest growing areas. "Remember that the lower number is colder and the larger number is warmer—that's a good mental trick to remember how they work," say the O'Neals.
What is the difference between zone 5a and 5b? ›
Zone 5 has two subzones: 5a and 5b. Zone 5a has an average minimum temperature between negative fifteen and negative twenty degrees Fahrenheit. Zone 5b has a low minimum temperature between negative ten and negative fifteen degrees Fahrenheit.
How accurate are hardiness zones? ›
However, while hardiness zones are relatively accurate for flat areas like the East Coast, they are trickier to evaluate when it comes to the western part of the US because of the influence of the Rockies and other mountains. Mountains create microclimates of elevation and differentiation in precipitation.
Is zone 6 colder than zone 8? ›
A plant that is hardy in zone 8 – 10 probably will not survive a zone 6 winter since there is a 20 degree average low difference, but you may find success growing a zone 8 – 10 plant in zone 7, or a zone 7 plant in zone 6.
How are USDA hardiness zones determined? ›
Hardiness zones in this map are based on the average annual extreme minimum temperature during a 30-year period in the past, not the lowest temperature that has ever occurred in the past or might occur in the future.
Where is Zone 15 in Maine? ›
District 15 shall be that portion of the state located within the following bounds: Beginning at the point where State Highway #110 intersects the Maine-New Hampshire border in Newfield; then following the Maine-New Hampshire border northerly to the Government Rd in Stow; then following the Government Rd easterly to ...
District 27 includes all coastal islands in Washington County, as well as those coastal islands located in Franklin, Sullivan, Sorrento, Gouldsboro, and Winter Harbor in Hanco*ck County. WMD 27 is located on the Delorme Maine Atlas and Gazetteer Maps # 16.
What is the climate zone of Maine? ›
1): the Northern zone has a continental climate with cold winters and is influenced by air masses from the west and north; the Southern Interior zone has the warmest summer weather and is influenced by air masses from the south and west; and the Coastal zone has a maritime climate which moderates summer and winter ...
What hardiness zone is Maine? ›
Maine spans Plant Hardiness Zones 3-6. Each zone is based on the 30-year average of the single coldest temperature recorded each winter. Zone 3 is 10 degrees F colder than Zone 4, etc. In addition, each zone is split in half.
What zone is the coldest? ›
Cold Hardiness zones are based on the average annual minimum temperature in a given area of the country, with USDA Zone 1 being the coldest at minus 50 degrees F and USDA Zone 13 the warmest at above 60 degrees F.
Which is the most coldest zone? ›
The frigid zone is the coldest heat zone on the earth. It found one each in the two hemispheres. The Frigid zone in the northern hemisphere lies between Arctic Circle and the North pole and in the southern hemisphere between Antarctic Circle and South pole.
Where is Zone 4a in Maine? ›
Related Maine Maps:
| Maine Location | USDA Hardiness Zone(s) |
|---|
| Greenville | Zone 4a |
| Guilford | Zone 4b |
| Hallowell | Zone 5a, 5b |
| Hampden | Zone 5a, 5b |
142 more rowsHere in Portland Oregon, the USDA hardiness zone is 8b (with average low temperatures from 15 to 20 degrees Fahrenheit). There are many microclimates within Portland, so keep in mind that the hardiness guides can be seen as recommendations.
What hardiness zone is Bangor Maine? ›
According to the 2023 USDA Hardiness Zone Map Bangor, Maine is in Zones 5a (-20°F to -15°F). There is no change from the 2012 USDA Hardiness Zone Map which has Bangor in also in Zones 5a (-20°F to -15°F).
