Our Pepper Grow Planner turns your zip code or town into a planting calendar for a specific pepper: when to start seeds, when to transplant, when to expect a first harvest, and whether that harvest lands before frost. This page explains where every number comes from, how the planner puts them together, and where its limits are.
The short version: frost and temperature data come from NOAA, growing figures for each pepper come from university extension services and seed companies that state how they count, and the planner never fills a gap with a guess. When we don’t have a sourced figure, the planner says so.
Frost dates
Frost dates come from NOAA’s 1991–2020 U.S. Climate Normals, the official 30-year climate averages for U.S. weather stations. For each station, NOAA publishes the dates by which the last spring freeze (32°F) has passed, and the first fall freeze has arrived, at nine probability levels from 10% to 90%.
Your zip code is matched to the nearest station that has this data, using the U.S. Census Bureau’s center point for each zip code area. The planner tells you which station it used, how far away it is, and its elevation. Most zip codes are within about 12 km of a station; 90% are within about 23 km.
The risk setting picks which of NOAA’s levels to plan around. At the default 50% level, there’s an even chance of a frost after the spring date, and an even chance of one before the fall date. A lower risk level gives a later spring date and an earlier fall date, which means a shorter season but less chance of losing plants to frost.
Places where frost doesn’t come every year
In warm places, NOAA’s frost dates only describe the years that have a freeze. Tampa’s station, for example, has freeze dates on record, but freezes happen there in only about a third of years. Using those dates as-is would make frost look far more likely than it is.
So the planner scales each station’s frost odds by how often it freezes at all. If a station freezes in 35% of years and you plan at a 50% risk level, the planner treats the season as frost-free, because even the worst case is less likely than the risk you chose. The same adjustment is used in the date check and the U.S. map.
When the planner flags a result
The planner warns you when:
- another station within 25 km has a last-frost date three or more weeks different, which usually means elevation or terrain is changing things quickly where you are
- your zip code or town covers a large area, so frost timing may vary across it
- the nearest station is more than 50 km away
In any of those cases, a frost date you know from your own garden is likely more accurate. You can enter it instead.
Transplant date
Frost passing isn’t the only test. Peppers also need warm nights. Most of the extension sources we use give 50°F as the minimum overnight low for transplanting peppers (University of Minnesota Extension, UGA Extension). NMSU puts nights closer to 55°F, so the planner shows that later date as an option too.
The transplant date is the later of two dates: the day after your last spring frost, and the day NOAA’s normal daily low at your station first reaches 50°F. In many northern and mountain areas, nights stay cool for weeks after the last frost, and the gap can be large.
Seed starting, germination and harvest timing
Each pepper’s growing figures (germination time, when to start seeds, days to harvest, plant height and container suitability) come from university extension publications and seed companies. We follow a few rules:
- Every figure has a source, listed under Sources on each plan.
- Days to harvest must say what they count from. Seed companies usually count peppers from transplant, but not all do, and mixing the two moves harvest dates by about two months. A days-to-harvest figure that doesn’t state its basis isn’t used.
- Seed-start timing must say whether it counts back from the last frost or from transplanting. When nights stay cool for more than two weeks after the last frost, the planner counts back from your transplant date instead, so seeds aren’t started far too early.
- Where we don’t have a figure for a specific pepper, germination and seed-start timing fall back to general figures for chile peppers from NMSU’s Chile Pepper Institute and other extension sources, and the plan labels them as general figures. Harvest timing never falls back. If we don’t have it, the planner says so.
- Figures added or rechecked in October 2026 were matched word for word against the live source page. Figures we couldn’t match, or that appear word for word on every product page from the same company, aren’t used.
Where sources disagree, the planner shows the full range rather than picking one.
Does it fit your season?
The planner compares the days from your transplant date to your first fall frost with the pepper’s days to harvest:
- Fits: the whole harvest window lands before first frost.
- Tight: only the early end of the window fits.
- Won’t ripen: even the early end comes after first frost.
“What can I grow?” runs this test for every pepper with harvest timing and lists the ones that fit your season, with filters for heat and for peppers that do well in containers.
The U.S. map on each plan runs the same test for every county, using the station nearest the county’s center, the 50% frost dates and the 50°F night rule. Because it uses standard settings, it can differ from your own plan.
Rain, humidity and heat
- Rain. Monthly normal precipitation from NOAA, shown as inches per week for the months of your season, against the inch a week peppers need (UMass Extension, SDSU Extension). If your station has no rain record, the nearest station that does is used, and the planner says which.
- Humidity. The planner uses NOAA’s normal dew point, not relative humidity, and describes it with the National Weather Service’s scale: up to 55°F is dry and comfortable, 55–65°F is sticky, and 65°F and up means lots of moisture in the air, becoming oppressive. Humid, rainy weather favors bacterial leaf spot and anthracnose (NMSU, NC State Extension).
- Heat. When normal daily highs at your station reach 90°F or more during your season, the planner shows that stretch of dates, because very little pepper fruit sets in that heat (NC State Extension, Oklahoma State Extension, University of Wyoming Extension). It does the same when normal lows stay at 75°F or above.
Soil and winter
Peppers do best in well-drained soil with a pH of about 6.0 to 7.0 (Oklahoma State Extension, University of Missouri Extension). The planner links to the soil-testing lab for your state, or to your state extension’s list of labs where there isn’t a public one. That list was checked by hand.
Your USDA plant hardiness zone comes from the 2023 USDA Plant Hardiness Zone Map, produced by the PRISM Climate Group at Oregon State University. UF/IFAS Extension lists peppers as perennials in zones 9b through 11b; colder than that, they’re grown as annuals.
The zone map on each plan colors every county by the zone most of its zip codes fall in, using the same 2023 map. Your own zone comes from your zip code, so it can differ from your county’s color.
A fall crop
Where normal summer highs reach 90°F inside your season and there’s room for a second planting, the planner shows a fall planting date. It uses Mississippi State Extension’s rule: count back from the first fall frost by the days to harvest, plus 10 days, because plants grow a little slower in fall. Texas A&M AgriLife’s crop guides give a similar window: about 85 to 100 days before first frost for hot peppers and 90 to 100 for bell peppers.
Stretching a short season
When a pepper is tight or won’t fit, the planner lists peppers that do fit your season and some ways to stretch it. The figures come from UConn, Oklahoma State, University of Wisconsin, NMSU and Utah State extension publications, and one peer-reviewed bell pepper trial (Roberts and Anderson, HortScience, 1994) that found lower yields on black plastic mulch in hot Oklahoma summers.
This week’s forecast
The forecast check is the only part of the planner that uses live data. When you press the button, the planner asks the National Weather Service’s public forecast service for the next seven nights’ lows at your zip code’s center point and compares them with 50°F and 32°F. Nothing is sent until you press it, and the location sent is the center of your zip code area, rounded to about a kilometer.
Limits
- Climate normals are 30-year averages. Any given year can run early or late.
- NOAA’s frost dates are for 32°F at the station. Low spots, open ground and places away from buildings can frost on nights the station doesn’t.
- Days to harvest are seed-company and extension figures for typical conditions. Weather, variety and care all move them.
- A station can be several kilometers away and at a different elevation from your garden. The planner shows the distance and elevation so you can judge.
- Some peppers on the list are sold under several names or as several varieties, and growing figures can differ between them.
Data sources
- NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals
- U.S. Census Bureau, 2026 Gazetteer files (zip code areas and places)
- USDA Plant Hardiness Zone Map (2023), PRISM Climate Group, Oregon State University
- National Weather Service forecast API (api.weather.gov)
- University extension services and seed companies, listed under Sources on each plan
