Northern Hemisphere Planting Calendar — What to Sow Each Month
A Northern Hemisphere planting calendar tells you exactly which vegetables, herbs, and flowers to start indoors, direct-sow, or transplant outdoors each month. The core logic relies on each crop's offset from the last spring frost date: cool-season crops (lettuce, kale, peas) thrive March–April and August–September; warm-season crops (tomatoes, peppers, corn, squash) go in from May–June once soil exceeds 60 °F. Use this calculator to avoid guesswork — select a month and get actionable sowing advice calibrated to the Northern Hemisphere growing season.
In the Northern Hemisphere, the main planting windows are: **January–February** — start onions, leeks, and broad beans indoors; **March–April** — direct-sow peas, lettuce, radishes; **May–June** — transplant tomatoes, peppers, corn, and squash after last frost (typically May 1–15 for USDA Zones 5–7); **July–August** — start fall brassicas indoors, direct-sow turnips and kale; **September–October** — plant garlic and winter spinach; **November–December** — rest and plan. Cool-season crops tolerate soil as cold as 40 °F; warm-season crops need soil above 60 °F.
When to use this calculator
- A home gardener in Chicago (Zone 6a, last frost ~May 1) wants to know when to start tomato seedlings indoors — answer: 6–8 weeks before May 1 = mid-March.
- A backyard farmer in Seattle (Zone 8b, last frost ~March 15) needs to schedule successions of lettuce every 2 weeks from February through April to avoid bolting in summer heat.
- A community garden coordinator in Dallas (Zone 8a) is planning a fall garden and needs to know the latest date to direct-sow winter squash before first autumn frost (~November 15) — counting 90 days back = mid-August.
- A beginner gardener wants a month-by-month checklist of what to plant, transplant, and harvest without needing to calculate frost dates manually.
Worked Example — April, USDA Zone 6 (Chicago)
- Select month: April
- The calculator returns: Tomato, pepper, corn
- April is spring in the Northern Hemisphere — warm-season seedlings (tomatoes, peppers) are still indoors under grow lights, hardening off in the final 2 weeks before the May 1 last-frost date
- Direct-sow outdoors in April: peas, lettuce, spinach, radishes, beets (all tolerate soil at 40–50 °F)
- Do NOT transplant tomatoes outdoors until soil reaches 60 °F — typically 2 weeks after last frost = mid-May
How it works
3 min readMonthly Planting Guide — Northern Hemisphere (Zones 5–8)
The planting calendar maps each month to the crops best suited for that seasonal phase, based on USDA Hardiness Zone data and each crop's frost tolerance and days-to-maturity.
Core formulas:
Indoor Start Date = Last Spring Frost − Indoor Lead Time (weeks)
Earliest Outdoor Sow = Last Spring Frost − Frost Tolerance Buffer
Latest Fall Sow = First Fall Frost − Days to Maturity − 14 days---
Reference Table — What to Plant Each Month (Zones 5–8)
| Month | Season Phase | Start Indoors | Direct Sow / Transplant Outdoors | Soil Temp |
|---|---|---|---|---|
| January | Deep winter | Onions, leeks, celery (8–10 wks ahead) | — | N/A |
| February | Late winter | Peppers, eggplant (10–12 wks); broccoli | Cold frames: spinach, mâche | 35–40 °F |
| March | Early spring | Tomatoes, basil (6–8 wks) | Peas, radishes, lettuce, kale | 40–50 °F |
| April | Spring | Cucumbers, squash, melons (3–4 wks) | Beets, carrots, Swiss chard, spinach | 50–60 °F |
| May | Late spring | — | Tomatoes, peppers, beans, corn, squash | 60–70 °F |
| June | Early summer | Fall broccoli, cabbage (for Aug transplant) | Sweet potatoes, basil, more beans | 65–75 °F |
| July | Summer | Kale, collards (for fall) | Beans (succession), cucumbers | 70–80 °F |
| August | Late summer | — | Fall broccoli, kale, turnips, beets, carrots | 65–75 °F |
| September | Early fall | — | Spinach, garlic (cloves), lettuce, radishes | 50–60 °F |
| October | Fall | — | Garlic (main planting), cover crops (rye, clover) | 40–55 °F |
| November | Late fall | — | Overwintering onion sets (Zones 7+) | 35–45 °F |
| December | Winter | — | Paperwhites, cold-stratify seeds | N/A |
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Frost Tolerance at a Glance
| Tolerance Level | Crops | Min Soil Temp |
|---|---|---|
| Hardy (survive 25–28 °F) | Kale, collards, garlic, leeks, parsnips | 35 °F |
| Semi-hardy (survive 29–32 °F) | Broccoli, cabbage, lettuce, peas, spinach, beets | 40 °F |
| Tender (damaged below 32 °F) | Tomatoes, peppers, cucumbers, beans, corn, squash | 60 °F |
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Worked Examples
April, Chicago (Zone 6a, last frost May 1)
September, Atlanta (Zone 7b, first fall frost ~November 20)
June, Pacific Northwest (Zone 8b, Seattle)
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Common Mistakes
1. Planting warm-season crops too early. Tomatoes below 55 °F suffer chilling injury — check soil temp, not just air temp.
2. Ignoring Days to Maturity for fall planting. A 100-day butternut squash planted August 15 in Zone 6 (first frost October 1) gets only 47 days — it won't mature.
3. Confusing "last frost date" with a guarantee. USDA/NOAA dates are the 50th percentile. Conservative gardeners use the 10% probability date, 2–4 weeks later.
4. Skipping hardening off. Indoor seedlings need 7–14 days of gradual outdoor exposure before transplanting.
5. Sowing all lettuce at once. Stagger sowing every 14 days from March through May for continuous harvest.
Frequently asked questions
What can I plant in April in the Northern Hemisphere?
April is ideal for direct-sowing cool-season crops outdoors: peas, lettuce, spinach, radishes, beets, Swiss chard, and carrots (USDA Zones 5–8, soil at 40–50 °F). Simultaneously, keep warm-season transplants (tomatoes, peppers) growing indoors under lights — they go outdoors after last frost in May.
When should I start tomatoes indoors?
Start tomatoes indoors 6–8 weeks before your last spring frost date. For most of USDA Zones 5–7, that means mid-February to mid-March. Transplant outdoors 2 weeks after last frost, once soil reaches 60 °F. Starting earlier leads to leggy, root-bound seedlings.
What is the last frost date and how do I find mine?
The last spring frost date is the historical date after which freezing temperatures (≤32 °F) are unlikely, based on 30-year NOAA climate normals. USDA Zone 5 averages May 15; Zone 6 averages May 1; Zone 7 averages April 15; Zone 8 averages March 15. Find your exact date at the USDA Plant Hardiness Zone Map (planthardiness.ars.usda.gov) or NOAA's frost probability tool.
Can I plant tomatoes in May everywhere in the Northern Hemisphere?
No. May transplanting suits USDA Zones 5–7. In Zone 4 (Minnesota, northern Canada), last frost can extend to late May — push transplant dates to early June. In Zones 9–10 (Southern California, South Florida), tomatoes go in February–March and again August–September to avoid summer heat above 95 °F, which prevents fruit set.
What is the difference between 'start indoors' and 'direct sow'?
'Start indoors' means germinating seeds in trays inside (6–12 weeks before outdoor planting) — used for slow-growing crops like tomatoes (6–8 wks), peppers (10–12 wks), and celery (10–12 wks). 'Direct sow' means placing seeds straight into garden soil — used for crops that dislike transplanting (carrots, beets, corn, beans) or that grow fast enough not to need a head start (radishes ripen in 25–30 days).
How do I plan a fall garden — when do I start in late summer?
Count backwards from your first fall frost date using each crop's Days to Maturity (DTM): Latest Sow Date = First Fall Frost − DTM − 14 days (extra time for slower fall growth). Example: first frost October 15, broccoli DTM 80 days → plant by July 27. Fast crops like spinach (40–50 days) can go in as late as mid-September in Zone 6.
Which crops can survive a light frost?
Hardy crops (survive 25–28 °F): kale, collards, Brussels sprouts, parsnips, garlic, leeks. Semi-hardy crops (survive 29–32 °F): broccoli, cabbage, carrots, lettuce, peas, spinach, beets. Tender crops (damaged below 32 °F): tomatoes, peppers, cucumbers, beans, basil, corn, squash. This determines which crops you plant earliest in spring and latest in fall.
How does USDA Plant Hardiness Zone affect my planting calendar?
USDA Plant Hardiness Zones (updated 2023, based on 1991–2020 climate normals) divide North America into 13 zones by average annual minimum winter temperature. Zone 5 has ~150 frost-free days; Zone 9 has 270+. Your zone determines last/first frost dates, which anchor all planting calculations. Find your zone at planthardiness.ars.usda.gov.
What should I plant in October in the Northern Hemisphere?
October is primarily for garlic (the main planting window — cloves go in 4–6 weeks before ground freezes, for summer harvest). It is also the time to plant cover crops (winter rye, crimson clover) to protect and enrich soil over winter. In Zones 7+, overwintering onion sets can go in. Most vegetable sowing ends in October; the focus shifts to soil care.