Sources & attribution

PlantingWindow computes from public data and shows its work. This page is generated from the same manifest and crop registry the calculations use, so it cannot drift out of sync with the product.

Climate, hardiness & geography data

USDA Plant Hardiness Zone Map — required attribution

Suggested citation, reproduced as requested by the map's publishers: “USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture. Accessed from https://planthardiness.ars.usda.gov/.” The map was jointly developed by USDA-ARS and Oregon State University's PRISM Climate Group. PlantingWindow displays zone values from the official ZIP-code dataset without alteration, does not reproduce the official map image, and displays no USDA or OSU logos; per the publishers' conditions, this site is not the official USDA Plant Hardiness Zone Map and nothing here implies USDA endorsement.

NOAA/NCEI Climate Normals

Freeze-date probabilities, growing-season lengths, and freeze-occurrence probabilities are from the NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, Annual/Seasonal product (v1.0.1, by-station archive). NOAA data are U.S. Government works. Product page.

U.S. Census Bureau geography

ZCTA interior points and the national place list come from the Census Bureau's 2025 Gazetteer files (ZCTAs are 2020-census based). These are public U.S. Government data.

Crop-timing sources (university extension)

Each crop's methods cite the following publications directly; access dates shown. Registry version 1.0.0.

• Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)
  Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.
• Penn State Extension (York County Master Gardeners): Vegetable Seed Planting Guide (accessed 2026-07-24)
  Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.
• University of New Hampshire Extension: Growing Vegetables: When to Plant Your Vegetable Garden [fact sheet] (accessed 2026-07-24)
  Per-crop 'time from seed to transplant' and 'safe to set out in garden' relative to last frost.
• University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)
  Weeks needed to grow vegetable transplants indoors (Table 2).
• Oklahoma State University Extension: Culinary Herbs for Oklahoma Gardens: Culture, Use and Preservation (accessed 2026-07-24)
  Table 1 planting times relative to last spring frost for common herbs.
• University of Illinois Extension: Dill (Herbs) (accessed 2026-07-24)
  "Sow the seeds in the spring one to two weeks before the last frost."
• University of Wisconsin–Madison Division of Extension (Wisconsin Horticulture): Parsley, Petroselinum crispum (accessed 2026-07-24)
  "Start seeds indoors 8-10 weeks before last frost."
• Iowa State University Extension and Outreach: Growing Basil in the Home Garden (accessed 2026-07-24)
  "Start seeds indoors 4 or 5 weeks before the last frost date." "Plant basil outdoors after all danger of frost is past."
• Iowa State University Extension and Outreach: Growing Watermelon in the Home Garden (accessed 2026-07-24)
  "Plant melons after the danger of frost is past and soil temperatures have warmed to 60 to 70°F." "Start seeds indoors 3 to 4 weeks before the anticipated outdoor planting date."
• University of Georgia Cooperative Extension: Growing Home Garden Sweet Corn (Circular 905) (accessed 2026-07-24)
  "Wait until at least two weeks after the last average killing frost before planting."
• University of Georgia Cooperative Extension: Home Garden Green Beans (Circular 1006) (accessed 2026-07-24)
  "Green beans are a warm season crop that can be planted as soon as the danger of frost has passed in the spring."
• N.C. Cooperative Extension (NC State Extension, Macon County): Starting Your Strawberry Patch (accessed 2026-07-24)
  "Plant 1-year old dormant plants about three or four weeks (mid-April) before the average date of the last frost."
• Utah State University Extension: How to Grow Strawberries in Your Garden (accessed 2026-07-24)
  "Bare root dormant plants are transplanted in early spring. Since the plants are dormant, there is no need to wait until after the risk of spring frost has passed."
• University of Minnesota Extension: Growing garlic (accessed 2026-07-24)
  "Plant cloves in the fall, usually one or two weeks after the first killing frost."
• University of Minnesota Extension: Growing onions (accessed 2026-07-24)
  "You can also raise your own transplants by starting seed indoors 10 to 12 weeks before planting outside."
• University of Minnesota Extension: Growing potatoes (accessed 2026-07-24)
  "Plant seed pieces as soon as the soil warms" — soil-temperature caveat to the frost-relative rule.
• University of Wisconsin-Madison Division of Extension: Marigolds - Wisconsin Horticulture (accessed 2026-07-25)
  "Marigolds can be direct seeded into garden soil when soil temperatures are >65°F or seeds can be started indoors ~8 weeks prior to transplanting outdoors after the threat of frost has passed."
• University of Minnesota Extension: Marigolds (accessed 2026-07-25)
  "Marigold seeds can be started indoors about 10 weeks prior to the anticipated outdoor planting date."
• Iowa State University Extension and Outreach: When can I plant marigolds outdoors? | Yard and Garden (accessed 2026-07-25)
  "Plant marigold seedlings outdoors after the danger of frost is past."
• University of Illinois Extension: How to grow sunflowers at home - A great addition to any garden | Good Growing (accessed 2026-07-25)
  "Sunflowers are typically direct-seeded after the danger of frost has passed (early to mid-May). They can also be started indoors, typically 2-3 weeks before planting outdoors, if you want to get a head start."
• NC State Extension: Helianthus annuus (Common Sunflower) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
  "This annual is best planted by seed after the last frost in the spring, and harvested before the first frost in the fall."
• University of Georgia Cooperative Extension: Growing Sunflowers in the Home Garden (Circular 1121) (accessed 2026-07-25)
  "Sunflowers should be planted several weeks after the last frost."
• North Carolina Cooperative Extension, Pender County Center: Growing Flowers and Vegetables From Seed (accessed 2026-07-25)
  "Large seeded flowers and vegetables are the easiest to grow and include cucumbers, zucchini, squash, melons, cosmos, marigolds, nasturtium, zinnias, and sunflowers. To get a head start on the season, seeds of these varieties can be sown indoors in mid-March to transplant outdoors after the threat of frost."
• NC State Extension: Cosmos bipinnatus (Cut Leaf Cosmos, Garden Cosmos, Mexican Aster, Tall Cosmos) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
  "Sow the seeds outdoors after the danger of frost is past and when the soil has warmed to at least 65 degrees."
• NC State Extension: Cosmos sulphureus (Klondike Cosmos, Orange Cosmos, Sulphur Cosmos, Yellow Cosmos) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
  "Sow the seeds outdoors after the danger of frost is past and when the soil has warmed to at least 65 degrees."
• Utah State University Extension: Cosmos in the Garden (accessed 2026-07-25)
  "Grow plants from seed sown directly into the soil once all danger of frost has passed."
• University of Wisconsin-Madison Division of Extension: Nasturtium, Tropaeolum species - Wisconsin Horticulture (accessed 2026-07-25)
  "Seed can be sown directly in the garden in late spring to early summer once all danger of frost has passed or started indoors in peat pots 4 to 6 weeks before the date of the last expected spring frost."
• University of Illinois Extension: Nasturtium | Herbs (accessed 2026-07-25)
  "Because nasturtium does not transplant well, it is suggested to directly sow seeds into the garden after danger of frost is past."
• Iowa State University Extension and Outreach: Direct Seeding Vegetables and Annuals - Preparation and Care | Yard and Garden (accessed 2026-07-25)
  "Cool-season annuals, like viola and nasturtium, can be sown 3 to 4 weeks before the last frost."
• Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)
  "Table 1: Starting times for seeds grown indoors and in cold frames, shown as number of weeks to start seed before average frost-free date."
• University of Illinois Extension: Annuals — Flowers (accessed 2026-07-25)
  "Ornamental cabbage and kale, pansy, snapdragon, sweet alyssum, calendula and dusty miller"
• NC State Extension: Extension Gardener Handbook, Ch. 10: Herbaceous Ornamentals (accessed 2026-07-25)
  "Hardy annuals are the most cold-tolerant. They tolerate light frost and some freezing weather without being killed. In most cases, hardy annuals are planted in the fall or in the spring before the last frost date."
• University of Maryland Extension: Production of Celosia as a Cut Flower (accessed 2026-07-25)
  "Sow Celosia 4 weeks before the last frost date."
• University of Minnesota Extension: Celosia (accessed 2026-07-25)
  "Celosia seeds can be started indoors about 10 weeks prior to the anticipated outdoor planting date."
• University of Illinois Extension: Celosia — Flowers (accessed 2026-07-25)
  "Tender Annual"
• University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture): Sweet Alyssum, Lobularia maritima (accessed 2026-07-25)
  "Transplants that have been hardened off can be placed in the garden a week or two before the average last frost, otherwise tender transplants should be protected until add danger of frost is past."
• Clemson Cooperative Extension Home & Garden Information Center: Sweet Alyssum (accessed 2026-07-25)
  "Sweet alyssum can easily be grown from seed and should be directly sown in the garden several weeks before the last frost date in spring."
• Clemson Cooperative Extension Home & Garden Information Center: Growing Annuals (accessed 2026-07-25)
  "Half-hardy annuals – such as allysum and dianthus -can tolerate light frost and are usually planted in early spring for spring and early summer color."
• University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture: Sage, Salvia officinalis (accessed 2026-07-25)
  "To grow from seed, either plant directly in the garden on the average date of last frost or start indoors 6 to 8 weeks before then."
• University of Maryland Extension: Care of Herbs and Starting Herbs from Seed (accessed 2026-07-25)
  "Basil, parsley, sage, marjoram, and many other herbs can be started indoors and planted outside after the danger of frost has passed."
• University of Minnesota Extension: Growing chives in home gardens (accessed 2026-07-25)
  "The easiest and most successful way of growing chives is planting rooted clumps in spring after frost danger has passed."
• University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture: Chives, Allium schoenoprasum (accessed 2026-07-25)
  "Seeds can be started indoors a few weeks before the average date of last frost to be planted outside after the danger of frost is past, or can be direct seeded once the soil is warm."
• Utah State University Extension: How to Grow Chives in Your Garden (accessed 2026-07-25)
  "Transplants need 6-8 weeks of growth before planting in the garden."
• Utah State University Extension: How to Grow French Tarragon in Your Garden (accessed 2026-07-25)
  "Transplant French tarragon in the spring, after the last frost, to ensure the survival of tender young shoots."
• Virginia Cooperative Extension, Virginia Tech: Herb Culture and Use (Publication 426-420) (accessed 2026-07-25)
  "In addition, many culinary herbs, such as tarragon, can only be propagated asexually; seed-grown plants lack the oils that give them flavor."
• NC State Extension, North Carolina Extension Gardener Plant Toolbox: Origanum majorana (Knotted Marjoram, Marjoram, Pot Marjoram, Sweet Marjoram) (accessed 2026-07-25)
  "To plant from seed, start seeds indoors about 6 to 8 weeks prior to the last spring frost date."
• Clemson University Cooperative Extension, Home & Garden Information Center: Herbs (accessed 2026-07-25)
  "Start seed indoors 6 to 8 weeks before planting or set transplants out after the last killing frost."
• University of Illinois Extension: Savory: Summer | Herbs (accessed 2026-07-25)
  "Summer savory is grown from seeds sown directly in the garden or indoors and then transplanted after danger of frost is past."
• Texas A&M AgriLife Extension Service: Herbs (Easy Gardening series, EHT-079) (accessed 2026-07-25)
  "Seed after danger of frost in full sun; space 6–9 in. apart"
• University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture: Lemon Balm, Melissa officinalis (accessed 2026-07-25)
  "Lemon balm can be started from seed sown indoors about 4 to 6 weeks before the last spring frost, although seeds may be somewhat slow to germinate."
• University of Illinois Extension: Borage | Herbs (accessed 2026-07-25)
  "Borage is easily grown from seed started indoors or directly sown in the garden after frost is past."
• Cornell University Garden-Based Learning (Cornell Cooperative Extension): Arugula growing guide (accessed 2026-07-25)
  "Make new plantings every 2 to 3 weeks for a continuous supply until about a month before your average first frost date."
• University of Arkansas System Division of Agriculture, Cooperative Extension Service: Chinese Cabbage (Home Gardening Series, FSA6066) (accessed 2026-07-25)
  "Transplant two to three weeks before the last frost-free date and before the plants are too old (four to five weeks)."
• Clemson Cooperative Extension, Home & Garden Information Center: Chinese Vegetables (accessed 2026-07-25)
  "Chinese cabbage is best sown in late summer and autumn rather than spring. If seed is sown in spring, young plants may bolt if they are frosted or exposed to long, cold nights."
• Clemson Cooperative Extension, Home & Garden Information Center: Cabbage & Chinese Cabbage (accessed 2026-07-25)
• Utah State University Extension: Suggested Vegetable Planting Dates for Utah (accessed 2026-07-25)
  "Semi-Hardy (Plants a week or two after 'A' group or about 2 weeks before average last spring frost.)"
• University of Minnesota Extension: Growing lettuce, endive and radicchio in home gardens (accessed 2026-07-25)
  "For a fall crop, sow seed about three months before the average first fall frost date."
• University of Arkansas System Division of Agriculture, Cooperative Extension Service: Endive-Escarole (Home Gardening Series, FSA6068) (accessed 2026-07-25)
  "They must be grown as an early spring or fall crop."
• Utah State University Extension: How to Grow Garden Cress in Your Garden (accessed 2026-07-25)
  "Garden cress does not tolerate frost so plant near the frost free date for your area."
• University of Arkansas System Division of Agriculture, Cooperative Extension Service: Garden Cress (Home Gardening Series, FSA6084) (accessed 2026-07-25)
  "Planting – seed shallow depth after danger of frost"
• Colorado State University Extension (Colorado Master Gardener): CMG GardenNotes #720: Vegetable Planting Guide (accessed 2026-07-25)
  "Hardy Vegetables ... Crops: broccoli, cabbage, kohlrabi, onions, lettuce, peas, radish, spinach, turnips"
• Purdue University Extension, Department of Horticulture and Landscape Architecture: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-25)
  "Table 2. Cool season plants for late-summer or fall planting (plant at least 4-8* weeks before first fall frost) (See Figure 2)"
• University of California Cooperative Extension, UC Master Gardener Program of Sonoma County: Celeriac (accessed 2026-07-25)
  "Sow seed indoors as early as 10 weeks before the average last frost date in spring."
• University of Illinois Extension: Turnip | Home Vegetable Gardening (accessed 2026-07-25)
  "For fall harvest, plant rutabagas about 100 days before the first frost, and plant turnips about 3 to 4 weeks later."
• University of Georgia Extension: Growing Rutabagas in the Home Garden (Circular 942), Terry Kelley and Robert Westerfield (accessed 2026-07-25)
  "Rutabagas should be seeded 2 ½ to three months before a heavy frost."
• University of Arkansas System Division of Agriculture, Cooperative Extension Service: Salsify (Home Gardening Series), FSA6094, Craig R. Andersen (accessed 2026-07-25)
  "Plant the seed in deep, well-prepared fertile soil in late spring or summer (about 100 days before freezing weather)."
• University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture): Fennel, Foeniculum vulgare, Susan Mahr (accessed 2026-07-25)
  "Plants can be started indoors 4 to 6 weeks before the last spring frost."
• Utah State University Extension: Planting and Spacing — Legumes (Vegetable Guide) (accessed 2026-07-25)
  "Plant the cool-season legumes several weeks before and the warm-season legumes around the frost-free date for the location."
• University of Maryland Extension: Growing Southern Peas in a Home Garden (accessed 2026-07-25)
  "Wait until all danger of frost is passed and the soil has warmed before planting."
• Alabama Cooperative Extension System: Grow More Peas (Southern) (accessed 2026-07-25)
  "Plant April through July after any danger of frost has passed."
• University of Arkansas Cooperative Extension Service: Southern Peas (FSA-6020), Home Gardening Series (accessed 2026-07-25)
  "For fall planting, plant about 65 to 75 days prior to the average frost date to be sure of production."
• Texas A&M AgriLife Extension: Southern Pea (Cowpea) — Commercial and Specialty Crop Guides (accessed 2026-07-25)
  "Optimum Time Soil temperature > 65°F and danger of frost is over"
• Utah State University Extension: Peanuts in the Garden (accessed 2026-07-25)
  "Sow seeds 1½ inches deep, 18 inches apart, with 4 seeds per mound when soil temperatures are above 65° F (usually around the last frost)."
• Alabama Cooperative Extension System: Cover Crops: Legumes (accessed 2026-07-25)
  "Plant hairy vetch 15 to 45 days before the killing frost."
• UMass Amherst Center for Agriculture, Food, and the Environment: Cover Crops — growing tips (accessed 2026-07-25)
  "As a general rule, cover crops should be planted about 30 days before the first expected frost date."
• Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)
  "*Plants best suited for direct seeding in garden two weeks prior to the average frost-free date."
• University of Wisconsin-Madison Division of Extension: Calendula, Calendula officinalis – Wisconsin Horticulture (accessed 2026-07-25)
  "Seeds can be sown directly in the garden just before last frost date, but for earlier bloom start seeds indoors about 6 to 8 weeks before last frost."
• Utah State University Extension: How to Grow English Lavender in Your Garden (accessed 2026-07-25)
  "Transplant new plants after the last spring frost."
• University of Maryland Extension: Growing Leafy Greens in a Home Garden (accessed 2026-07-25)
  "Planting leafy green facts - collards, kale, mustard, turnips, and pac choi"
• University of New Hampshire Cooperative Extension: Cool Season Vegetables (accessed 2026-07-25)
  "Asian greens (like bok choi), and kohlrabi, are known to bolt prematurely if they are exposed to cooler temperatures, so they should be set out after last frost."
• Utah State University Extension: How to Grow Chicory in Your Garden (accessed 2026-07-25)
  "Seeded radicchio may be planted 3-4 weeks before the last frost-free date for the growing area."
• NC State Extension: Zinnia elegans (Common Zinnia, Zinnia) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)
  "Sow seed directly in the ground after the last frost date."
• University of Wisconsin-Madison Division of Extension: Zinnias - Wisconsin Horticulture (accessed 2026-07-25)
  "Seed can be direct sown in the garden or landscape after the danger of frost has passed in spring, and it can also be started indoors 4 to 6 weeks earlier."
• Iowa State University Extension and Outreach: Direct Seeding Vegetables and Annuals - Preparation and Care | Yard and Garden (accessed 2026-07-25)
  "Direct-seed most annual flowers after the threat of frost is past in the spring and when the soil warms ups."

Extension publications are cited as sources; the institutions have not reviewed and do not endorse this site.

Illustration & iconography

The site's crop icons, marks, and decorative graphics are original vector artwork created for PlantingWindow. Full asset provenance is documented in the repository's ASSET_SOURCES.md. (An earlier design used a CC BY-SA 4.0 Wikimedia Commons photograph by Kolforn; it no longer appears on the site.)

Type

Fraunces (The Fraunces Project Authors) and Inter (Rasmus Andersson et al.), both under the SIL Open Font License 1.1, self-hosted.

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