Frost Dates & Planting Calendar for Riverton, WY
Plan your garden around Riverton, WY's typical frost-free growing season, using NOAA climate normals and a 42-crop planting calendar built for this location.
Last Spring Frost
May 12
Safe May 26
Typical May 12
Risky May 1
First Fall Frost
September 24
Safe Sep 11
Typical Sep 24
Risky Oct 7
Growing Season
132 days
Typical last frost to typical first frost.
USDA Hardiness Zone
Zone 5a
A classic four-season climate with cold winters and a solid summer growing season.
Data: NOAA station RIVERTON, WY US, 0.8 km away.
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days until the typical last spring frost
Monthly Temperatures
Avg. high
Avg. temp
Avg. low
Planting Calendar
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Tomato | Mar 17 – Mar 31 | — | May 19 – May 26 | — | 60–85 days | Start indoors 6-8 weeks before last frost; transplant out 1-2 weeks after last frost once soil has warmed. |
| Pepper | Mar 3 – Mar 17 | — | May 19 – Jun 2 | — | 60–90 days | Slow to germinate; start indoors 8-10 weeks before last frost. Transplant only once nights stay above 55F, 1-3 weeks after last frost. |
| Eggplant | Mar 3 – Mar 17 | — | May 26 – Jun 2 | — | 65–85 days | Warm-season crop, similar timing to pepper; needs consistently warm soil (65F+) to transplant. |
| Cucumber | Apr 14 – Apr 21 | May 19 – May 26 | May 19 – May 26 | — | 50–65 days | Can be started indoors 3-4 weeks before transplanting, or direct-sown 1-2 weeks after last frost once soil is warm. |
| Zucchini | Apr 21 – Apr 28 | May 19 – Jun 2 | May 19 – May 26 | — | 45–55 days | Fast-growing squash; direct sow 1-3 weeks after last frost, or start indoors 2-3 weeks early for a head start. |
| Winter Squash | Apr 14 – Apr 21 | May 19 – Jun 2 | May 19 – May 26 | — | 80–110 days | Long season; direct sow after soil warms, or start indoors 3-4 weeks before last frost in short-season climates. |
| Pumpkin | — | May 19 – Jun 2 | — | — | 90–120 days | Direct sow 1-3 weeks after last frost; back-time from your first fall frost so the 90-120 day maturity window lands before it. |
| Watermelon | Apr 14 – Apr 21 | — | May 26 – Jun 2 | — | 70–90 days | Needs warm soil (65F+); start indoors 3-4 weeks before last frost, transplant 2-3 weeks after last frost. |
| Cantaloupe | Apr 14 – Apr 21 | — | May 26 – Jun 2 | — | 70–90 days | Same warm-soil requirements as watermelon; avoid disturbing roots when transplanting. |
| Corn | — | May 12 – May 26 | — | — | 60–100 days | Direct sow at last frost to 2 weeks after, once soil reaches 60F; does not transplant well. Succession sow every 2 weeks. |
| Green Bean | — | May 12 – May 26 | — | — | 50–65 days | Direct sow at last frost to 2 weeks after, once soil has warmed; frost-tender, do not rush. |
| Pea | — | Mar 31 – Apr 14 | — | — | 55–70 days | Cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Lettuce | — | Apr 14 – Apr 28 | — | Jul 30 – Aug 13 | 45–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. Also transplantable from indoor starts. |
| Spinach | — | Mar 31 – Apr 14 | — | Jul 30 – Aug 13 | 40–50 days | Very cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Kale | — | Apr 14 – Apr 28 | — | Jul 16 – Jul 30 | 50–65 days | Cold-hardy; direct sow 2-4 weeks before last frost or start indoors for earlier transplants. |
| Arugula | — | Apr 14 – Apr 28 | — | Aug 13 – Aug 20 | 30–40 days | Fast-growing, cold-tolerant green; direct sow 2-4 weeks before last frost, succession sow every 2-3 weeks. |
| Swiss Chard | — | Apr 21 – May 5 | — | — | 50–60 days | Fairly cold-hardy; direct sow 1-3 weeks before last frost. Tolerates light frost in fall too. |
| Broccoli | Mar 24 – Apr 7 | — | Apr 21 – Apr 28 | Jul 23 – Jul 30 | 55–80 days | Start indoors 5-7 weeks before last frost; transplant out 2-3 weeks before last frost (hardens off to light frost). |
| Cauliflower | Mar 24 – Apr 7 | — | Apr 28 – May 5 | Jul 16 – Jul 23 | 55–85 days | Fussier than broccoli about temperature swings; start indoors 5-7 weeks before last frost, transplant 1-2 weeks before last frost. |
| Cabbage | Mar 24 – Apr 7 | — | Apr 14 – Apr 28 | Jul 16 – Jul 30 | 60–100 days | Cold-hardy; start indoors 5-7 weeks before last frost, transplant 2-4 weeks before last frost. |
| Brussels Sprouts | Mar 24 – Apr 7 | — | Apr 21 – May 5 | — | 90–110 days | Long-season crop best timed to mature after a light fall frost for sweetest flavor; start indoors 5-7 weeks before last frost. |
| Carrot | — | Apr 14 – Apr 28 | — | Jul 2 – Jul 16 | 60–80 days | Direct sow only (does not transplant); sow 2-4 weeks before last frost, as soon as soil can be worked. |
| Beet | — | Apr 14 – Apr 28 | — | Jul 16 – Jul 30 | 50–65 days | Direct sow 2-4 weeks before last frost; tolerates light frost. |
| Radish | — | Apr 7 – Apr 21 | — | Aug 13 – Aug 27 | 22–30 days | Very fast and cold-hardy; direct sow 3-5 weeks before last frost, as soon as soil can be worked. |
| Turnip | — | Apr 14 – Apr 28 | — | Jul 16 – Jul 30 | 40–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. |
| Onion | Mar 3 – Mar 17 | — | Apr 14 – Apr 28 | — | 90–120 days | Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings. |
| Garlic | — | — | — | Aug 27 – Sep 10 | 240–270 days | Fall-planted crop only; not planted in spring in most climates. |
| Potato | — | Apr 14 – Apr 28 | — | — | 70–120 days | Plant seed potatoes 2-4 weeks before last frost, as soon as soil can be worked and is above 45F; light frost on emerging foliage is usually tolerated. |
| Sweet Potato | — | — | May 26 – Jun 9 | — | 90–120 days | Set out slips 2-4 weeks after last frost once soil is thoroughly warm (65F+); very frost/cold sensitive. |
| Asparagus | — | — | Apr 14 – Apr 28 | — | 730–1095 days | Perennial; plant crowns 2-4 weeks before last frost as soon as soil can be worked. Takes 2-3 years to full production. |
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Basil | Mar 31 – Apr 7 | — | May 19 – May 26 | — | 50–70 days | Very frost/cold sensitive; start indoors 5-6 weeks before last frost, transplant only after all danger of frost (1-2 weeks after) and nights stay warm. |
| Cilantro | — | Apr 21 – May 5 | — | Jul 30 – Aug 13 | 45–70 days | Cool-season, bolts in heat; direct sow 1-3 weeks before last frost, succession sow through spring. |
| Parsley | Mar 17 – Mar 31 | — | Apr 28 – May 5 | — | 70–90 days | Slow to germinate; start indoors 6-8 weeks before last frost, transplant 1-2 weeks before last frost (biennial, cold-tolerant). |
| Dill | — | Apr 21 – May 5 | — | — | 40–60 days | Taprooted, does not transplant well; direct sow 1-3 weeks before last frost, succession sow through summer. |
| Oregano | Mar 17 – Mar 31 | — | May 12 – May 19 | — | 80–90 days | Perennial herb; start indoors 6-8 weeks before last frost, transplant around/just after last frost date. |
| Thyme | Mar 17 – Mar 31 | — | May 12 – May 19 | — | 85–95 days | Perennial herb, slow from seed; start indoors 6-8 weeks before last frost, transplant around/after last frost. |
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Sunflower | — | May 19 – Jun 2 | — | — | 70–100 days | Direct sow 1-3 weeks after last frost once soil has warmed; taprooted, resents transplanting. |
| Zinnia | Apr 14 – Apr 21 | May 19 – Jun 2 | May 19 – May 26 | — | 60–70 days | Frost-tender; direct sow 1-3 weeks after last frost, or start indoors 3-4 weeks early for earlier blooms. |
| Marigold | Mar 31 – Apr 14 | — | May 19 – May 26 | — | 45–60 days | Frost-tender; start indoors 4-6 weeks before last frost, transplant after all frost danger has passed. |
| Cosmos | Apr 14 – Apr 21 | May 19 – Jun 2 | May 19 – May 26 | — | 60–90 days | Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early. |
| Nasturtium | — | May 19 – Jun 2 | — | — | 50–65 days | Frost-tender, resents root disturbance; direct sow 1-3 weeks after last frost once soil has warmed. |
| Dahlia | — | — | May 19 – Jun 2 | — | 90–120 days | Plant tubers 1-3 weeks after last frost once soil is warm (60F+); very frost-sensitive. |
Date ranges are estimates based on university extension guidelines and this city's NOAA frost normals — not a guarantee. Scroll to see all columns on narrow screens.
Frequently Asked Questions
When is the last frost in Riverton, WY?
Based on 1991–2020 NOAA climate normals for the RIVERTON, WY US station, the last spring frost in Riverton typically falls around May 12. A cautious gardener might wait until May 26 (only a 10% chance of a later frost), while May 1 marks an earlier, higher-risk planting date.
When is the first frost in Riverton, WY in fall?
The first fall frost in Riverton typically arrives around September 24. To stay safe, assume frost could start as early as September 11; in milder years it can hold off until October 7.
How long is the growing season in Riverton, WY?
Riverton's average frost-free growing season is about 132 days, running from the typical last spring frost (May 12) to the typical first fall frost (September 24).
What USDA hardiness zone is Riverton, WY in?
Riverton, WY is in USDA plant hardiness zone 5a, per the USDA's 2023 Plant Hardiness Zone Map. A classic four-season climate with cold winters and a solid summer growing season.