Zone 3 in numbers
Zone 3 covers places whose coldest winter night averages -40 to -30°F. Across the ZIP codes in this zone, NOAA's 1991 to 2020 normals give:
- Zone 3a: average last spring frost May 28, first fall frost Sep 11, and a median of 108 frost-free days.
- Zone 3b: average last spring frost May 17, first fall frost Sep 23, and 128 frost-free days.
That makes 3b about 11 days earlier in spring and 12 days later in fall, three weeks more season in all. Zone 3a is also a small sample, 19 ZIP codes against 221 in 3b, so if you are in 3a, a ZIP code lookup in the seed starting calculator is worth more than the median.
When to start seeds indoors in zone 3
The tables count back from the average last frost:
Start indoors = last frost date − weeks indoors
At 6 to 8 weeks indoors:
- Tomatoes and peppers are sown Apr 2 to Apr 16 in 3a and Mar 22 to Apr 5 in 3b. They go out 2 weeks after the last frost, on Jun 11 in 3a and May 31 in 3b.
- Leeks, at 10 to 12 weeks, are the first seeds of the year: Mar 5 to Mar 19 in 3a and Feb 22 to Mar 8 in 3b.
- Onions and kale follow in March and early April.
Hardy crops go outside well before the frost date. In 3a, peas are sown outdoors Apr 30 to May 14, and onion transplants go out Apr 30 to May 14.
Where the season runs out
Zone 3 is the zone where the calculator starts to flag crops that may not ripen. It checks each crop's days to maturity against the days left between planting out and the first fall frost.
- At average dates in 3a, tomatoes and peppers set out on Jun 11 have 92 days before Sep 11. Peppers need 70 to 85 days from transplanting, so they fit, with little to spare.
- At the safer dates (Jun 2 and Sep 3), the gap shrinks to 79 days. Peppers and eggplant become tight, and the 125-day potatoes no longer fit.
- At the safest dates (Jun 13 and Aug 26), only 60 days remain after transplanting. Tomatoes, peppers, eggplant, melons and watermelons all come up short.
In 3b the picture is easier: 115 days after transplanting at average dates, and 88 even at the safest dates.
The practical answer is to choose early varieties, start peppers at the early end of their window, and use the safer column only for the transplant date. Seeds sown indoors carry no frost risk.
Fall crops in zone 3
Fall sowing counts back from a first frost that comes early. At average dates in 3a:
- Brussels sprouts, at 17 weeks before frost, are sown by May 15. In practice that is a spring sowing.
- Kale and collards are sown by Jun 12.
- Peas for fall go in Jul 10 to Jul 17.
Zone 3b adds about 12 days to each.
Next zone over
If your ZIP code sits near the edge, compare zone 4. The planner below starts on 3a; switch it to 3b, or enter your ZIP code for your nearest station.