Frost Dates for Prosser, WA 99350
Last spring frost April 22 · First fall frost October 12 · 173 frost-free days · USDA Zone 7b
ZIP 99350 has about 14,800 people.
Moderate season: 173 frost-free days. Spring frost risk spans April 5–May 9 (34 days). Fall frost risk spans September 29–October 25 (26 days).
Frost probability for 99350
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | May 9 | April 22 | April 5 |
| Fall (first frost) | September 29 | October 12 | October 25 |
Dates come from NOAA 1971–2000 freeze probabilities at SUNNYSIDE (30.5 km away); the 50% date is the median year.
Which crops fit a 173-day season in Prosser
In Prosser (173 frost-free days, a moderate season), 30 of 56 planner crops fit outright, 25 get two plantings, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | Mar 18 | May 6–May 13 | 131 | fits: 80 days to maturity, 131 available after May 6. | Jun 12 |
| Pepper | Mar 11 | May 6–May 13 | 131 | fits: 75 days to maturity, 131 available after May 6. | Jun 17 |
| Lettuce | Feb 25 | Mar 25–Apr 1 | 208 | two-plantings: Plant Mar 25 and again by Aug 21; both mature before Oct 19. | Aug 21 |
| Carrots | — | Apr 1–Apr 8 | 215 | fits: 70 days to maturity, 215 available after Apr 1. | Aug 10 |
| Cucumber | Apr 1 | May 6–May 13 | 145 | two-plantings: Plant May 6 and again by Jul 16; both mature before Sep 28. | Jul 16 |
| Beans | — | Apr 29–May 13 | 159 | two-plantings: Plant Apr 29 and again by Jul 23; both mature before Oct 5. | Jul 23 |
| Peas | — | Feb 25–May 6 | 236 | fits: 65 days to maturity, 236 available after Feb 25. | Aug 1 |
| Zucchini | Apr 8 | May 6–May 13 | 145 | two-plantings: Plant May 6 and again by Jul 21; both mature before Sep 28. | Jul 21 |
| Onion | Jan 28 | Mar 25–Apr 8 | 208 | fits: 100 days to maturity, 208 available after Mar 25. | — |
| Spinach | — | Feb 25–Apr 15 | 250 | two-plantings: Plant Feb 25 and again by Sep 9; both mature before Nov 2. | Sep 9 |
| Kale | Feb 11 | Mar 25–Apr 8 | 222 | two-plantings: Plant Mar 25 and again by Aug 25; both mature before Nov 2. | Aug 25 |
| Broccoli | Feb 25 | Mar 25–Apr 8 | 208 | fits: 80 days to maturity, 208 available after Mar 25. | Jul 17 |
| Cabbage | Feb 25 | Mar 25–Apr 8 | 222 | fits: 70 days to maturity, 222 available after Mar 25. | Aug 10 |
| Radish | — | Feb 25–May 20 | 236 | two-plantings: Plant Feb 25 and again by Sep 10; both mature before Oct 19. | Sep 10 |
| Beets | — | Feb 25–May 20 | 236 | two-plantings: Plant Feb 25 and again by Aug 11; both mature before Oct 19. | Aug 11 |
| Potatoes | — | Apr 8–Apr 15 | 194 | fits: 90 days to maturity, 194 available after Apr 8. | — |
| Garlic | — | Oct 12 | 278 | overwinter: Plant Oct 12 to Nov 2; harvest the following summer. | Nov 2 |
| Strawberry | — | Mar 18–May 13 | 229 | perennial: A perennial: plant Mar 18; it fruits from the following year and keeps producing for several years. | — |
| Corn | Mar 25 | Apr 29–May 6 | 145 | fits: 75 days to maturity, 145 available after Apr 29. | Jun 24 |
| Pumpkin | Apr 8 | May 6–May 6 | 138 | fits: 100 days to maturity, 138 available after May 6. | May 30 |
| Cauliflower | Mar 11 | Apr 15–Apr 29 | 187 | fits: 75 days to maturity, 187 available after Apr 15. | Jul 22 |
| Swiss Chard | Feb 25 | Apr 8–Apr 8 | 194 | two-plantings: Plant Apr 8 and again by Aug 11; both mature before Oct 19. | Aug 11 |
| Arugula | — | Feb 25–May 20 | 250 | two-plantings: Plant Feb 25 and again by Sep 9; both mature before Nov 2. | Sep 9 |
| Brussel Sprouts | Feb 25 | Mar 25–Apr 8 | 222 | fits: 100 days to maturity, 222 available after Mar 25. | Jul 11 |
| Butternut Squash | Apr 8 | May 6–May 13 | 138 | fits: 100 days to maturity, 138 available after May 6. | May 30 |
| Eggplant | Mar 4 | May 6–May 13 | 131 | fits: 70 days to maturity, 131 available after May 6. | Jun 22 |
| Okra | Mar 25 | Apr 29–May 6 | 152 | two-plantings: Plant Apr 29 and again by Jul 21; both mature before Sep 28. | Jul 21 |
| Basil | Mar 18 | May 13–May 13 | 138 | two-plantings: Plant May 13 and again by Jul 16; both mature before Sep 28. | Jul 16 |
| Cilantro | — | Mar 25–Apr 15 | 208 | two-plantings: Plant Mar 25 and again by Aug 16; both mature before Oct 19. | Aug 16 |
| Parsley | Feb 11 | Apr 29–May 6 | 173 | fits: 70 days to maturity, 173 available after Apr 29. | Jul 27 |
| Celery | Feb 11 | Apr 29–May 13 | 173 | fits: 120 days to maturity, 173 available after Apr 29. | Jun 7 |
| Scallions | Feb 11 | Mar 25–Apr 8 | 222 | two-plantings: Plant Mar 25 and again by Aug 20; both mature before Nov 2. | Aug 20 |
| Turnip | — | Mar 25–Apr 8 | 222 | two-plantings: Plant Mar 25 and again by Aug 30; both mature before Nov 2. | Aug 30 |
| Kohlrabi | — | Mar 11–Mar 25 | 236 | two-plantings: Plant Mar 11 and again by Aug 25; both mature before Nov 2. | Aug 25 |
| Bok Choy | Mar 25 | Apr 15–Apr 22 | 187 | two-plantings: Plant Apr 15 and again by Aug 21; both mature before Oct 19. | Aug 21 |
| Collards | Feb 11 | Mar 25–Apr 8 | 222 | two-plantings: Plant Mar 25 and again by Aug 20; both mature before Nov 2. | Aug 20 |
| Cantaloupe | Apr 8 | May 6–May 13 | 131 | fits: 85 days to maturity, 131 available after May 6. | Jun 7 |
| Chives | Jan 28 | Apr 29–May 6 | 187 | fits: 90 days to maturity, 187 available after Apr 29. | — |
| Dill | — | Feb 25–May 20 | 236 | two-plantings: Plant Feb 25 and again by Aug 11; both mature before Oct 19. | Aug 11 |
| Oregano | Feb 11 | Apr 29–May 6 | 187 | fits: 80 days to maturity, 187 available after Apr 29. | — |
| Rosemary | Jan 28 | Apr 29–May 6 | 173 | fits: 80 days to maturity, 173 available after Apr 29. | — |
| Sage | Feb 25 | Apr 29–May 6 | 187 | fits: 75 days to maturity, 187 available after Apr 29. | — |
| Thyme | Feb 11 | Apr 29–May 6 | 187 | fits: 90 days to maturity, 187 available after Apr 29. | — |
| Calendula | Mar 11 | Apr 8–Apr 22 | 194 | two-plantings: Plant Apr 8 and again by Aug 16; both mature before Oct 19. | Aug 16 |
| Cosmos | Mar 25 | Apr 22–May 6 | 159 | two-plantings: Plant Apr 22 and again by Jul 16; both mature before Sep 28. | Jul 16 |
| Lavender | Jan 28 | Apr 22–May 6 | 194 | fits: 90 days to maturity, 194 available after Apr 22. | — |
| Marigolds | Mar 11 | Apr 22–Apr 29 | 159 | two-plantings: Plant Apr 22 and again by Jul 26; both mature before Sep 28. | Jul 26 |
| Melons | Apr 8 | May 6–May 13 | 131 | fits: 85 days to maturity, 131 available after May 6. | Jun 7 |
| Mint | — | Apr 22–May 6 | 194 | fits: 90 days to maturity, 194 available after Apr 22. | — |
| Nasturtiums | Mar 25 | Apr 22–Apr 29 | 159 | two-plantings: Plant Apr 22 and again by Jul 21; both mature before Sep 28. | Jul 21 |
| Pole Beans | — | Apr 29–May 13 | 152 | fits: 65 days to maturity, 152 available after Apr 29. | Jul 11 |
| Spaghetti Squash | Apr 8 | May 6–May 13 | 138 | fits: 90 days to maturity, 138 available after May 6. | Jun 9 |
| Sunflowers | — | Apr 22–May 6 | 159 | fits: 70 days to maturity, 159 available after Apr 22. | Jul 6 |
| Tomatillos | Feb 25 | Apr 29–May 6 | 138 | fits: 75 days to maturity, 138 available after Apr 29. | Jun 17 |
| Watermelon | Apr 8 | Apr 29–May 6 | 138 | fits: 80 days to maturity, 138 available after Apr 29. | Jun 12 |
| Yellow Squash | Apr 8 | May 6–May 13 | 145 | two-plantings: Plant May 6 and again by Jul 21; both mature before Sep 28. | Jul 21 |
| Zinnias | Mar 25 | Apr 22–May 6 | 159 | two-plantings: Plant Apr 22 and again by Jul 16; both mature before Sep 28. | Jul 16 |
Month by month in Prosser
| Month | What to do |
|---|---|
| January | Start indoors: Chives (Jan 28), Lavender (Jan 28), Onion (Jan 28), Rosemary (Jan 28). |
| February | Start indoors: Celery (Feb 11), Collards (Feb 11), Kale (Feb 11), Oregano (Feb 11), Parsley (Feb 11), Scallions (Feb 11), +8 more. Direct sow from: Arugula (Feb 25), Beets (Feb 25), Dill (Feb 25), Peas (Feb 25), Radish (Feb 25), Spinach (Feb 25). |
| March | Start indoors: Eggplant (Mar 4), Calendula (Mar 11), Cauliflower (Mar 11), Marigolds (Mar 11), Pepper (Mar 11), Basil (Mar 18), +7 more. Direct sow from: Kohlrabi (Mar 11), Cilantro (Mar 25), Turnip (Mar 25). Transplant from: Broccoli (Mar 25), Brussel Sprouts (Mar 25), Cabbage (Mar 25), Collards (Mar 25), Kale (Mar 25), Lettuce (Mar 25), +2 more. Plant: Strawberry (Mar 18). |
| April | Start indoors: Cucumber (Apr 1), Butternut Squash (Apr 8), Cantaloupe (Apr 8), Melons (Apr 8), Pumpkin (Apr 8), Spaghetti Squash (Apr 8), +3 more. Direct sow from: Carrots (Apr 1), Potatoes (Apr 8), Sunflowers (Apr 22), Beans (Apr 29), Pole Beans (Apr 29). Transplant from: Calendula (Apr 8), Swiss Chard (Apr 8), Bok Choy (Apr 15), Cauliflower (Apr 15), Cosmos (Apr 22), Lavender (Apr 22), +15 more. Last frost around April 22. |
| May | Transplant from: Butternut Squash (May 6), Cantaloupe (May 6), Cucumber (May 6), Eggplant (May 6), Melons (May 6), Pepper (May 6), +6 more. Last sowing dates: Butternut Squash (May 30), Pumpkin (May 30). |
| June | Last sowing dates: Cantaloupe (Jun 7), Celery (Jun 7), Melons (Jun 7), Spaghetti Squash (Jun 9), Tomato (Jun 12), Watermelon (Jun 12), +4 more. |
| July | Last sowing dates: Sunflowers (Jul 6), Brussel Sprouts (Jul 11), Pole Beans (Jul 11), Basil (Jul 16), Cosmos (Jul 16), Cucumber (Jul 16), +10 more. |
| August | Last sowing dates: Peas (Aug 1), Cabbage (Aug 10), Carrots (Aug 10), Beets (Aug 11), Dill (Aug 11), Swiss Chard (Aug 11), +9 more. |
| September | Last sowing dates: Arugula (Sep 9), Spinach (Sep 9), Radish (Sep 10). |
| October | Direct sow from: Garlic (Oct 12). First frost around October 12. |
| November | Last sowing dates: Garlic (Nov 2). |
| December | Clean up spent plants. Add compost to beds. Rest, review, and plan next year's garden. |
Frequently Asked Questions
What is the last frost date for Prosser, WA (ZIP 99350)?
The median last spring frost date for Prosser, WA (ZIP code 99350) is around April 22. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area. One year in ten frost ends before April 5; one in ten it runs past May 9.
What is the first fall frost date in Prosser, WA?
The median first fall frost date for Prosser, WA is around October 12. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses. The first frost arrives around September 29 in the earliest one-in-ten years, so cover tomatoes and peppers from then.
How long is the growing season in Prosser, WA?
The frost-free growing season in Prosser is about 173 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side. In Prosser (173 frost-free days, a moderate season), 30 of 56 planner crops fit outright, 25 get two plantings, 1 crop is perennial.
What USDA hardiness zone is Prosser, WA?
Prosser, WA is in USDA hardiness zone 7b (2023 USDA Plant Hardiness Zone Map). Zones come from the average coldest winter temperature, so they tell you which perennials survive the winter; the frost dates on this page tell you when to plant.
When should I start tomatoes indoors in Prosser, WA?
Start tomatoes indoors Mar 18 and plant out May 6 in Prosser. The planner uses the local median last frost and this crop's indoor-start and transplant offsets.
How many plantings of lettuce fit in Prosser?
Two: plant Mar 25 and again by Aug 21; both mature before Oct 19.
When do I plant garlic in Prosser?
Oct 12 to Nov 2; it overwinters and is ready the following summer.
Which nearby ZIP has a longer season?
West Richland (ZIP 99353) has 197 frost-free days, 24 more than Prosser (ZIP 99350). See West Richland ZIP 99353 frost dates
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