Overview

Rapid swings in temperature and precipitation are normal for Orange County, but create stressful conditions for plants. In addition to our routinely erratic weather, unusually severe events like a 100-year drought, a 100-year ice storm, and record summer heat have occurred recently. Resilient plants, careful siting, and good soil preparation are critical for long-term success.

USDA hardiness zone

7b on the 2012 map
average annual minimum temperature of 5–10°F, a half-zone warmer than the 1990 map

AHS heat zone

7 (61–90 days where temp. exceeds 86°F) Heat Zone Map

Ecoregion

45c (Carolina Slate Belt)

NC climate division

Northern Piedmont

Average first frost

October 21–31

Average last frost

April 11–20
It is best to wait until 2 weeks after Apr 20 to plant tender transplants.

Growing season

214 ± 14 days (reference period 1980–2016)

Plant suitability

Climate numbers provide a limited picture of whether a particular plant is adapted to our area. Plant Hardiness Zone Maps and Wikipedia discuss the shortcomings of traditional climate data in greater detail. Ornamentals provides online lists of locally-adapted plants and has a detailed discussion of factors that determine adaptation. We also have handouts on woody plants, perennials, and annuals that are adapted for our area. Adaption depends on all of the factors below:

  • winter hardiness
  • tolerance to heat, drought, humidity & tree root competition
  • disease resistance
  • sunlight & daylength requirements
  • dormancy/chilling requirements
  • soil preferences

Unique climate features

It is natural to think of the Triangle as a single climate region, but the topography of North Carolina creates distinct weather patterns that are not always shared between adjacent counties. Ice storms are a good example — Orange County lies near the center of an ice storm alley that affects NC unevenly. Severely damaging ice storms (more than ¾″ freezing rain) like the ones in 2002 and 2014 occur approximately every 10 years in Orange County, but only every 15 years in Durham County.

likelihood of damaging ice storm State Climate Office of NC A Winter Weather Climatology for the Southeastern United States

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