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About PlantingCalc

PlantingCalc provides free gardening calculators powered by USDA hardiness zone data, NOAA frost dates, and agricultural extension research. Every tool on this site is designed to help home gardeners make data-driven decisions, from soil preparation to harvest timing.

Our Data Sources

  • USDA Plant Hardiness Zone Map (via phzmapi.org): determines your growing zone by ZIP code.
  • NOAA Frost Date Normals: average first and last frost dates for accurate planting windows.
  • University Agricultural Extension Publications: peer-reviewed spacing, fertilizer, and watering guidelines.
  • Open-source companion planting databases: research-backed companion and antagonist plant pairings.

Why Trust Our Calculators

  • Real government data: USDA zones and NOAA frost dates, not guesswork.
  • Open-source plant databases: transparent, verifiable information.
  • Transparent methodology: every calculation explains how it works.
  • Regularly updated: data refreshed to reflect the latest USDA and NOAA releases.

Who We Are

PlantingCalc is built by home gardeners who got tired of guessing. We maintain raised beds and in-ground gardens across multiple USDA zones, and we built these tools because we wanted the same data-driven planning resources that commercial growers have, without the $200/year software subscriptions.

Every calculator on this site is backed by published agricultural data, not guesswork. When we say “plant tomatoes 2 weeks after your last frost,” that comes from the same extension office guidelines that professional farmers follow.

How We Calculate

  • Frost dates are averaged from 30-year NOAA climate normals, cross-referenced with your USDA hardiness zone via the official phzmapi.org API.
  • Planting windows use the standard extension office formula: weeks before or after your local last frost date, calibrated per crop.
  • Spacing recommendations come from university agricultural extension publications (Cornell, UMass, UF/IFAS, Oregon State).
  • Fertilizer profiles are based on published NPK requirements per crop from soil science research and extension guides.
  • Watering estimates use base rates from agricultural research, adjusted by multipliers for climate, soil type, container vs. in-ground, and season.

Our Calculators