What zone 7 means
USDA's Plant Hardiness Zone Map "is based on the average annual extreme minimum winter temperature," shown in 10°F zones and 5°F half zones (USDA ARS). USDA's ZIP code search labels the two halves of zone 7 like this:
| Half zone | Average annual extreme minimum (°F) | (°C) |
|---|---|---|
| 7a | 0 to 5 | −17.8 to −15 |
| 7b | 5 to 10 | −15 to −12.2 |
Zone 7 takes in places as far apart as Philadelphia, Oklahoma City and Boise (USDA ZIP search, table below). The University of Idaho notes that Idaho alone runs from zone 3 to zone 7. For your own address, use the ZIP search on USDA's map; every zone below was checked that way in October 2026.
Zone 7 does not set your frost dates
A zone is a winter-cold number for choosing perennials. University of Idaho Extension: "Knowing your hardiness zone will not tell you how many frost-free days you will have." Frost dates and season length come from NOAA's Climate Normals, which give the last spring and first fall 32°F freeze at stated probabilities. The hardiness zones guide explains the difference.
Six zone 7 cities, side by side
Zone: USDA ARS ZIP search for the city ZIP shown (2023 map, 2012 zone in brackets); the airport ZIP of each station has the same 2023 half zone. Frost data: NOAA NCEI 1991–2020 normals, 32°F threshold. The 50% date is the median; a 10% spring date means a later freeze about 1 year in 10, and a 10% fall date a freeze that early about 1 year in 10 (NC State's guide to these tables).
| Place (ZIP) | Zone 2023 (2012) | Last spring freeze 50% (10%) | First fall freeze 50% (10%) | Season, days 50% (90%) |
|---|---|---|---|---|
| Philadelphia, PA (19107) | 7b (7b) | Apr 2 (Apr 13) | Nov 10 (Oct 30) | 224 (207) |
| Louisville, KY (40202) | 7a (6b) | Mar 31 (Apr 16) | Nov 7 (Oct 28) | 222 (202) |
| Nashville, TN (37203) | 7b (7a) | Mar 31 (Apr 16) | Nov 3 (Oct 22) | 217 (197) |
| St. Louis, MO (63101) | 7a (6b) | Apr 2 (Apr 17) | Nov 4 (Oct 23) | 215 (196) |
| Oklahoma City, OK (73102) | 7b (7a) | Apr 4 (Apr 20) | Nov 2 (Oct 21) | 213 (191) |
| Boise, ID (83702) | 7a (6b) | Apr 24 (May 9) | Oct 21 (Oct 5) | 179 (156) |
Stations: Philadelphia Intl AP, Louisville Intl AP, Nashville Intl AP, St. Louis Lambert Intl AP, Oklahoma City Will Rogers AP, Boise Air Terminal. NC State calls the 90% season the conservative one: at least that long in about 9 years out of 10.
What the table shows:
- Five of the six have a median last spring freeze between March 31 and April 4. Boise's is April 24, 20 to 24 days later, and its median season is 179 days against 213–224 for the others.
- Louisville and Boise are both 7a, yet their median seasons differ by 43 days.
- Five of the six moved up a half zone between the 2012 and 2023 maps; Philadelphia did not. Their frost dates come from NOAA's normals either way.
- 1. Half zone from USDA's ZIP search (2023 map): Philadelphia, Nashville and Oklahoma City are 7b; Louisville, St. Louis and Boise are 7a
- 2. Green bar: from the 50% last spring 32°F freeze to the 50% first fall freeze (NOAA NCEI 1991–2020), with NOAA's median season length
- 3. Red ticks: 10% dates, when a later spring or earlier fall freeze happens about 1 year in 10
- 4. Amber strip: the average last spring frost range Virginia Cooperative Extension gives for the half zone (7a April 15–25, 7b April 5–15); only Boise's median falls inside it
- 5. Season lengths range from 224 days (Philadelphia) to 179 (Boise) inside the same zone
Crop timing examples
Planting guides count from your own last frost date. UNH Extension's fact sheet sets lettuce transplants out 3–4 weeks before last frost, kale 4 weeks before, broccoli 2–4 weeks before, tomatoes and cucumbers 1–2 weeks after, peppers, basil and squash 2 weeks after, with cucumber and squash seed sown when "soil warms to 70°F." Applied to the NOAA 50% dates of an early and the latest city above (our arithmetic):
| Crop (UNH offset) | Nashville, last frost Mar 31 | Boise, last frost Apr 24 |
|---|---|---|
| Kale transplants (4 weeks before) | Mar 3 | Mar 27 |
| Lettuce transplants (3–4 weeks before) | Mar 3–10 | Mar 27–Apr 3 |
| Broccoli transplants (2–4 weeks before) | Mar 3–17 | Mar 27–Apr 10 |
| Tomato and cucumber transplants (1–2 weeks after) | Apr 7–14 | May 1–8 |
| Pepper, basil and squash transplants (2 weeks after) | Apr 14 | May 8 |
Same zone, more than three weeks apart. A cautious grower who uses the 10% date instead (April 16 in Nashville, May 9 in Boise) moves every row back about two more weeks. Enter your own dates in the planting calendar for 25 crops.
A zone 7 planting table, and why it needs a date check
Virginia Cooperative Extension's home garden planting guide (Jadrnicek and Hessler, 2025) keys planting dates to half zones. Selected rows from its zone 7a and 7b tables, which include a fall column:
| Crop | 7a spring | 7b spring | Fall (7a / 7b) |
|---|---|---|---|
| Peas, garden | Mar 1–Apr 1 | Feb 20–Apr 1 | Not recommended |
| Spinach | Mar 1–Apr 10 | Feb 10–Apr 1 | Sep 1–Oct 10 / Sep 10–Oct 20 |
| Collards, kale | Mar 1–Apr 20 | Feb 20–Apr 10 | Aug 1–Sep 10 / Aug 10–Sep 20 |
| Carrots | Mar 10–Apr 20 | Mar 1–Apr 10 | Jul 10–Aug 20 / Jul 20–Sep 1 |
| Broccoli (transplants) | Mar 20–May 1 | Mar 10–Apr 20 | Aug 1–Sep 1 / Aug 10–Sep 10 |
| Lettuce, head (transplants) | Mar 20–May 10 | Mar 10–May 1 | Aug 10–Sep 20 / Aug 20–Oct 1 |
| Tomatoes (transplants) | Apr 20–Jun 20 | Apr 10–Jun 20 | Jun 20–Aug 1 (both) |
| Peppers (transplants) | Apr 20–Jul 20 | Apr 10–Aug 1 | Not recommended |
| Garlic | Not recommended | Not recommended | Oct 1–Oct 30 (both) |
The table rests on frost ranges in the same guide, given as average (50% chance) dates: last spring frost April 15–25 and first fall frost October 15–25 for 7a; April 5–15 and October 25–November 5 for 7b. Compared with NOAA's medians above, the spring ranges run late: Louisville (March 31) and St. Louis (April 2) sit about two weeks before the 7a range, and Philadelphia, Nashville and Oklahoma City (March 31–April 4) fall just before the 7b range. Only Boise's April 24 lands inside its range. The guide itself says actual frost dates "will vary due to local conditions" and that Roanoke County alone spans four hardiness zones, with a 30-day planting difference.
Where the sources disagree
| Question | What the sources say |
|---|---|
| Last frost in zone 7a | Virginia Extension: April 15–25 (50%). NOAA 1991–2020 medians at 7a stations: Louisville March 31, St. Louis April 2, Boise April 24. |
| Last frost in zone 7b | Virginia Extension: April 5–15. NOAA medians: Nashville March 31, Philadelphia April 2, Oklahoma City April 4. |
| First fall frost in zone 7a | Virginia Extension: October 15–25. NOAA medians: Louisville November 7, St. Louis November 4, both later; Boise October 21, inside the range. |
| Tomato planting in Kentucky | University of Kentucky's guide gives earliest safe tomato transplant dates of April 20 (western), May 5 (central) and May 15 (eastern Kentucky), and maps last frost at 36°F rather than NOAA's 32°F. Even the western date is after Louisville's 10% date of April 16. |
| Oklahoma timing | Oklahoma State (Hillock and Sanders, 2021) gives one statewide window, tomato plants April 10–30 and pepper plants April 10–30 or later, earliest in the southeast and latest in the northwest. Oklahoma City's NOAA median is April 4 and its 10% date April 20. |
Oklahoma State adds a soil check: at least 40°F at seed depth for cool-season crops and 50°F for warm-season crops.
Using this page in a zone 7 garden
- Confirm your half zone with USDA's ZIP search; five of the six cities above changed between the 2012 and 2023 maps.
- Use the zone for perennials, the plants that stay in the ground over winter; that is what USDA designed the map for.
- Get frost dates for the station nearest you in distance and elevation; see how to find your frost dates.
- Pick a probability: NC State calls the 10% spring date the risk-averse choice, which suits frost-tender transplants.
- Check a zone-keyed chart's frost dates against your own; for five of the cities above, the chart's spring range began after NOAA's median.
- Plan a fall crop: Virginia's table lists late-summer sowings of spinach, kale, carrots and lettuce, and garlic in October. The zone 6 page compares six cities one zone colder.
Sources
- USDA Agricultural Research Service — USDA Plant Hardiness Zone Map (interactive map and ZIP code search)
- NOAA NCEI — Access Data Service: U.S. Climate Normals 1991–2020, annual/seasonal 32°F freeze dates and growing season probabilities for the six zone 7 stations named on this page (CSV)
- NOAA NCEI — Readme for the 1991–2020 normals files (definitions of PRBLST, PRBFST and PRBGSL)
- NC State Extension — Interpreting Freeze/Frost Probabilities from the National Centers for Environmental Information (AG-873)
- Virginia Cooperative Extension — Virginia's Home Garden Vegetable Planting Guide: Recommended Planting Dates and Amounts to Plant (426-331, Jadrnicek and Hessler, 2025)
- Oklahoma State University Extension — Oklahoma Garden Planning Guide (HLA-6004, Hillock and Sanders, 2021)
- University of Kentucky Cooperative Extension — Vegetable Gardening in Kentucky (ID-128, PDF)
- University of Idaho Extension — Spring Vegetable Planting Guide for Idaho (BUL 965, Andy West, 2020, PDF)
- University of New Hampshire Extension — Growing Vegetables: When to Plant Your Vegetable Garden (fact sheet)
All sources were opened and checked in October 2026. Rules and figures change; confirm with the original before acting.