In zone 3, plant tomato transplants outside from May 30 to June 6, one to two weeks after your last spring frost. Start seeds indoors from April 4 to April 18, and expect your first ripe tomatoes from about August 8.
Tomato dates for your ZIP code
Planting times based on university extension guidance (UNH, Cornell, Purdue, Minnesota, Nebraska and UMass Extension). Frost dates from NOAA 1991–2020 U.S. Climate Normals, nearest weather station. Zones derived from the 2023 USDA Plant Hardiness Zone Map data (PRISM Climate Group, Oregon State University). This is not the official USDA Plant Hardiness Zone Map.
Tomato timing in zone 3
| Task | When |
|---|---|
| Start indoors | April 4 – April 18 |
| Transplant outside | May 30 – June 6 |
| First harvest | August 8 – September 4 |
| Harden off seedlings | Over a few days to a week before transplanting |
| Stake or cage | At planting time |
| Pick green fruit | Before your first hard frost, around September 19 |
Most of zone 3 sees its last spring frost between May 21 and May 29, with a typical date of May 23. Tomatoes are killed by frost, so if your last frost comes late, plant toward the end of the window. The tool above uses the weather station closest to your ZIP code.
Why tomatoes wait for warm weather
Tomatoes are warm-season plants. A frost kills them, and cold soil and cold nights stall their growth even without frost. They do best once the soil is at least 65 °F and the air at least 60 °F, which is why transplants go out one to two weeks after the last spring frost rather than on the frost date itself.
Best tomato varieties for zone 3
Zone 3 summers are short, so days to maturity matter more than anything else. Pick varieties with the lowest number on the seed packet: early cherry types ripen about 50 days after transplanting and early full-size types about 60, while late varieties need 85 days or more.
- Bred for short, cool seasons: Early Sub-Arctic, Sub-Arctic Plenty, Immun Prior Beta and Farthest North.
- University of Idaho short-season varieties: Shoshone, Latah, Bonner, Sandpoint and Kootenai.
- Cherry tomatoes of almost any kind ripen sooner than large slicers.
How to plant tomatoes
- Start seeds indoors about six to eight weeks before your transplant date, in soil kept at 60–70 °F.
- Harden off the seedlings by setting them outside for a few hours a day, increasing the time over several days.
- Plant deep. Set plants at the depth of their first leaves. Leggy seedlings can be laid at an angle, with only the top 5–6 inches above the soil.
- Space them out: 1–3 feet apart, or 12–18 inches for staked indeterminate plants.
- Add support right away. Use 6-foot stakes for indeterminate tomatoes and cages 4–5 feet tall for determinate ones.
- Feed lightly at planting with a starter fertilizer, and again with nitrogen once the first fruit sets.
Zone 3 tomato tips
- Warm the soil first. Tomatoes do best once the soil is at least 65 °F and the air at least 60 °F. Black plastic mulch warms the soil, holds moisture and keeps weeds down; water through it.
- Use the warmest spot you have. The south side of a building gives tomatoes extra heat in cool areas.
- Shelter new transplants. A shingle or a cut-open milk carton on the windward side protects them for the first few days.
- Expect cool-night problems. Nights below 55 °F can cause blossom drop or misshapen fruit. They usually stop once nights warm up.
- Don’t overfeed. Too much nitrogen makes big vines and delays ripening, which you can’t afford in a short season.
Harvesting tomatoes
Pick tomatoes when they are fully colored, or when they are 60–90% colored and let them finish ripening indoors. Keep ripening and ripe tomatoes at 50–55 °F and out of the refrigerator, which ruins their flavor. When a frost is forecast, pick mature green fruit (the inside is filled with gel) and ripen it at 65–70 °F.
Tomato planting dates in nearby zones
- Zone 4May 23 – May 30
See dates for every zone on the tomatoes planting guide, or build a full schedule with the planting calendar.
Frequently asked questions
Is it too late to plant tomatoes in zone 3 in July?
It is getting late. If you plant in July, choose a cherry or early variety with 60 days or less to maturity, so the fruit can ripen before your first fall frost around September 19.
Can I grow tomatoes from seed sown outdoors in zone 3?
It isn’t worth it. Direct-seeded tomatoes take about 25 days longer to ripen than transplants, and zone 3 summers are too short for that.
When should I start tomato seeds indoors?
About six to eight weeks before you plan to transplant. The dates above count back from your zone’s transplant window.
Can I plant tomatoes before the last frost?
Not without protection. Frost kills tomato plants, and cold soil slows them down even when it doesn’t freeze. Wait one to two weeks after your last frost date.
What is the difference between determinate and indeterminate tomatoes?
Determinate plants grow about 3–4 feet tall and ripen most of their fruit over a couple of weeks. Indeterminate plants can reach 7–8 feet and keep producing until frost.
Why are my tomato flowers falling off?
Usually because of temperature. Nights below 55 °F and very hot weather both cause tomatoes to drop flowers without setting fruit.
Sources. Planting dates use the median frost dates of each USDA zone, calculated from NOAA climate data for every ZIP code in the zone.