{
  "slug": "frost-date-growing-window",
  "title": "Frost Date Growing Window Calculator",
  "heading": "Frost Date & Growing Season Window Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/frost-date-growing-window",
  "summary": "Find your frost-free growing window and safe planting dates from local frost dates.",
  "description": "Your growing season length is the gap between the average last spring frost and the average first fall frost, and it determines which crops you can grow to maturity outdoors without protection. This calculator takes your last and first frost dates (available from NOAA climate normals or your local extension office at a specific probability, typically 50%), computes total frost-free days, and back-calculates safe indoor-seed-starting and transplant dates for a crop given its days-to-maturity and recommended weeks-before-transplant. Gardeners routinely lose a crop by planting warm-season vegetables like tomatoes or peppers two weeks too early, right into a lingering frost — this tool builds in your buffer explicitly instead of relying on the calendar.",
  "formula": "Growing days = first fall frost − last spring frost; seed start date = last frost − weeks before transplant; harvest-by date = last frost + days to maturity.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=frost-date-growing-window",
  "inputs": [
    {
      "id": "lastFrost",
      "label": "Average last spring frost date",
      "kind": "date",
      "hint": null,
      "default": "2025-04-15"
    },
    {
      "id": "firstFrost",
      "label": "Average first fall frost date",
      "kind": "date",
      "hint": null,
      "default": "2025-10-20"
    },
    {
      "id": "daysToMaturity",
      "label": "Crop days to maturity",
      "kind": "number",
      "hint": null,
      "default": 75,
      "unit": null,
      "min": 20,
      "max": 200
    },
    {
      "id": "weeksBefore",
      "label": "Weeks to start seeds before transplant",
      "kind": "number",
      "hint": null,
      "default": 6,
      "unit": null,
      "min": 0,
      "max": 12
    },
    {
      "id": "buffer",
      "label": "Safety buffer after last frost",
      "kind": "number",
      "hint": null,
      "default": 7,
      "unit": "days",
      "min": 0,
      "max": 21
    }
  ],
  "outputs": [
    {
      "id": "growingDays",
      "label": "Frost-free growing days",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "seedStart",
      "label": "Start seeds indoors by",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "transplantDate",
      "label": "Safe outdoor transplant date",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "harvestBy",
      "label": "Estimated harvest-ready date",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "fits",
      "label": "Fits before first fall frost?",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Average last spring frost date: 2025-04-15",
      "Average first fall frost date: 2025-10-20",
      "Crop days to maturity: 75",
      "Weeks to start seeds before transplant: 6",
      "Safety buffer after last frost: 7 days"
    ],
    "outputs": [
      "Frost-free growing days: 188",
      "Start seeds indoors by: 2025-03-11",
      "Safe outdoor transplant date: 2025-04-22",
      "Estimated harvest-ready date: 2025-07-06",
      "Fits before first fall frost?: Yes, fits before first frost"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter average last spring frost date.",
      "Enter average first fall frost date.",
      "Enter crop days to maturity.",
      "Enter weeks to start seeds before transplant.",
      "Enter safety buffer after last frost (days).",
      "Read your frost-free growing days on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "lastFrost": "2025-04-15",
        "firstFrost": "2025-10-20",
        "daysToMaturity": 45,
        "weeksBefore": 4,
        "buffer": 4
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "lastFrost": "2025-04-15",
        "firstFrost": "2025-10-20",
        "daysToMaturity": 75,
        "weeksBefore": 6,
        "buffer": 7
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "lastFrost": "2025-04-15",
        "firstFrost": "2025-10-20",
        "daysToMaturity": 120,
        "weeksBefore": 10,
        "buffer": 11
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "Where do I find my local frost dates?",
      "a": "NOAA's National Centers for Environmental Information publishes 30-year climate normals by station and probability level (10%, 50%, 90% chance of frost). The 50% dates are the typical planting guide; use the 10% (later spring, earlier fall) dates if you want a more conservative, risk-averse window."
    },
    {
      "q": "Why add a buffer after the last frost date instead of planting exactly on it?",
      "a": "The 'average' last frost date means frost still occurs after it in roughly half of years. A 7-14 day buffer for tender crops like tomatoes and peppers accounts for that variance; hardy crops like lettuce and peas can be planted before the average date with little risk."
    },
    {
      "q": "What if my crop doesn't fit before first frost?",
      "a": "Shorten days-to-maturity by choosing an early variety, start seeds indoors earlier (increase weeks-before-transplant), use season-extension tools like row cover or a cold frame, or accept a fall harvest under frost protection instead of an open-field finish."
    },
    {
      "q": "Does this account for microclimates in my own yard?",
      "a": "No — station data is a regional average. South-facing walls, urban heat islands, and low-lying frost pockets can shift your actual frost dates by 1-3 weeks from the official station reading, so treat this as a starting estimate to refine with your own observations."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/heating-degree-days",
    "https://www.revenuelab.fyi/toolbox/evapotranspiration-irrigation"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Frost Date Growing Window Calculator (https://www.revenuelab.fyi/toolbox/frost-date-growing-window)"
}