Data Sources & Methodology

Learn about the scientific data and research that powers our planting recommendations.

USDA Plant Hardiness Zone Map
ZIP Code to Hardiness Zone Mapping
Primary Source
2023 Data

Our ZIP code to hardiness zone mapping is based on the official USDA Plant Hardiness Zone Map, which divides the United States into 13 zones based on average annual minimum winter temperatures.

Data Coverage:

  • • Complete U.S. ZIP code coverage
  • • Zones 3a through 10b
  • • Updated with 2023 climate data
  • • Temperature ranges from -40°F to 40°F
PRISM Climate Group
Frost Date Calculations
Climate Data
30-Year Average

Frost dates for each hardiness zone are derived from PRISM Climate Group data, which provides high-quality spatial climate datasets for the United States.

Frost Date Methodology:

  • • Based on 30-year climate normals
  • • 50% probability of last spring frost
  • • 50% probability of first fall frost
  • • Accounts for elevation and local geography
Crop Database
Planting and Growing Information
222+ Crops
Research-Based

Our comprehensive crop database combines information from multiple authoritative sources to provide accurate planting timing and growing requirements. We currently have 222 varieties.

Data Sources Include:

  • • University Extension Services
  • • USDA Agricultural Research
  • • Seed Company Guidelines
  • • Master Gardener Programs

Crop Categories:

  • • Vegetables (131 varieties)
  • • Herbs (32 varieties)
  • • Fruits (12 varieties)
  • • Flowers (47 varieties)
Data Accuracy & Limitations

Important Considerations:

  • • Frost dates are statistical averages - actual dates may vary by ±2 weeks
  • • Microclimates can significantly affect local growing conditions
  • • Soil temperature and moisture are equally important as air temperature
  • • Weather patterns are becoming less predictable due to climate change

While our data is based on the most reliable scientific sources available, gardening success depends on many local factors. We recommend using this tool as a starting point and adjusting based on your local observations and experience.

Attribution & Credits

USDA Agricultural Research Service

Plant Hardiness Zone Map and ZIP code data

PRISM Climate Group, Oregon State University

Climate data and frost date calculations

Cooperative Extension System

Crop timing and growing requirement data

This tool is provided for educational purposes. Always consult local extension services and experienced gardeners in your area for region-specific advice.

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