Frost Dates for Mason City, IA 50401
Last spring frost April 30 · First fall frost October 1 · 154 frost-free days · USDA Zone 5a
ZIP 50401 has about 28,700 people.
Moderate season: 154 frost-free days. Spring frost risk spans April 16–May 13 (27 days). Fall frost risk spans September 20–October 15 (25 days).
Frost probability for 50401
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | May 13 | April 30 | April 16 |
| Fall (first frost) | September 20 | October 1 | October 15 |
Dates come from NOAA 1971–2000 freeze probabilities at MASON CITY MUNI AP (10.2 km away); the 50% date is the median year.
Which crops fit a 154-day season in Mason City
In Mason City (154 frost-free days, a moderate season), 32 of 56 planner crops fit outright, 23 get two plantings, 1 crop is perennial.
| Crop | Start indoors | Plant out / sow | Days you have | Verdict | Last sow date |
|---|---|---|---|---|---|
| Tomato | Mar 26 | May 14–May 21 | 112 | fits: 80 days to maturity, 112 available after May 14. | Jun 1 |
| Pepper | Mar 19 | May 14–May 21 | 112 | fits: 75 days to maturity, 112 available after May 14. | Jun 6 |
| Lettuce | Mar 5 | Apr 2–Apr 9 | 189 | two-plantings: Plant Apr 2 and again by Aug 10; both mature before Oct 8. | Aug 10 |
| Carrots | — | Apr 9–Apr 16 | 196 | fits: 70 days to maturity, 196 available after Apr 9. | Jul 30 |
| Cucumber | Apr 9 | May 14–May 21 | 126 | fits: 60 days to maturity, 126 available after May 14. | Jul 5 |
| Beans | — | May 7–May 21 | 140 | two-plantings: Plant May 7 and again by Jul 12; both mature before Sep 24. | Jul 12 |
| Peas | — | Mar 5–May 14 | 217 | fits: 65 days to maturity, 217 available after Mar 5. | Jul 21 |
| Zucchini | Apr 16 | May 14–May 21 | 126 | two-plantings: Plant May 14 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Onion | Feb 5 | Apr 2–Apr 16 | 189 | fits: 100 days to maturity, 189 available after Apr 2. | — |
| Spinach | — | Mar 5–Apr 23 | 231 | two-plantings: Plant Mar 5 and again by Aug 29; both mature before Oct 22. | Aug 29 |
| Kale | Feb 19 | Apr 2–Apr 16 | 203 | two-plantings: Plant Apr 2 and again by Aug 14; both mature before Oct 22. | Aug 14 |
| Broccoli | Mar 5 | Apr 2–Apr 16 | 189 | fits: 80 days to maturity, 189 available after Apr 2. | Jul 6 |
| Cabbage | Mar 5 | Apr 2–Apr 16 | 203 | fits: 70 days to maturity, 203 available after Apr 2. | Jul 30 |
| Radish | — | Mar 5–May 28 | 217 | two-plantings: Plant Mar 5 and again by Aug 30; both mature before Oct 8. | Aug 30 |
| Beets | — | Mar 5–May 28 | 217 | two-plantings: Plant Mar 5 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Potatoes | — | Apr 16–Apr 23 | 175 | fits: 90 days to maturity, 175 available after Apr 16. | — |
| Garlic | — | Oct 1 | 259 | overwinter: Plant Oct 1 to Oct 22; harvest the following summer. | Oct 22 |
| Strawberry | — | Mar 26–May 21 | 210 | perennial: A perennial: plant Mar 26; it fruits from the following year and keeps producing for several years. | — |
| Corn | Apr 2 | May 7–May 14 | 126 | fits: 75 days to maturity, 126 available after May 7. | Jun 13 |
| Pumpkin | Apr 16 | May 14–May 14 | 119 | fits: 100 days to maturity, 119 available after May 14. | May 19 |
| Cauliflower | Mar 19 | Apr 23–May 7 | 168 | fits: 75 days to maturity, 168 available after Apr 23. | Jul 11 |
| Swiss Chard | Mar 5 | Apr 16–Apr 16 | 175 | two-plantings: Plant Apr 16 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Arugula | — | Mar 5–May 28 | 231 | two-plantings: Plant Mar 5 and again by Aug 29; both mature before Oct 22. | Aug 29 |
| Brussel Sprouts | Mar 5 | Apr 2–Apr 16 | 203 | fits: 100 days to maturity, 203 available after Apr 2. | Jun 30 |
| Butternut Squash | Apr 16 | May 14–May 21 | 119 | fits: 100 days to maturity, 119 available after May 14. | May 19 |
| Eggplant | Mar 12 | May 14–May 21 | 112 | fits: 70 days to maturity, 112 available after May 14. | Jun 11 |
| Okra | Apr 2 | May 7–May 14 | 133 | two-plantings: Plant May 7 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Basil | Mar 26 | May 21–May 21 | 119 | fits: 60 days to maturity, 119 available after May 21. | Jul 5 |
| Cilantro | — | Apr 2–Apr 23 | 189 | two-plantings: Plant Apr 2 and again by Aug 5; both mature before Oct 8. | Aug 5 |
| Parsley | Feb 19 | May 7–May 14 | 154 | fits: 70 days to maturity, 154 available after May 7. | Jul 16 |
| Celery | Feb 19 | May 7–May 21 | 154 | fits: 120 days to maturity, 154 available after May 7. | May 27 |
| Scallions | Feb 19 | Apr 2–Apr 16 | 203 | two-plantings: Plant Apr 2 and again by Aug 9; both mature before Oct 22. | Aug 9 |
| Turnip | — | Apr 2–Apr 16 | 203 | two-plantings: Plant Apr 2 and again by Aug 19; both mature before Oct 22. | Aug 19 |
| Kohlrabi | — | Mar 19–Apr 2 | 217 | two-plantings: Plant Mar 19 and again by Aug 14; both mature before Oct 22. | Aug 14 |
| Bok Choy | Apr 2 | Apr 23–Apr 30 | 168 | two-plantings: Plant Apr 23 and again by Aug 10; both mature before Oct 8. | Aug 10 |
| Collards | Feb 19 | Apr 2–Apr 16 | 203 | two-plantings: Plant Apr 2 and again by Aug 9; both mature before Oct 22. | Aug 9 |
| Cantaloupe | Apr 16 | May 14–May 21 | 112 | fits: 85 days to maturity, 112 available after May 14. | May 27 |
| Chives | Feb 5 | May 7–May 14 | 168 | fits: 90 days to maturity, 168 available after May 7. | — |
| Dill | — | Mar 5–May 28 | 217 | two-plantings: Plant Mar 5 and again by Jul 31; both mature before Oct 8. | Jul 31 |
| Oregano | Feb 19 | May 7–May 14 | 168 | fits: 80 days to maturity, 168 available after May 7. | — |
| Rosemary | Feb 5 | May 7–May 14 | 154 | fits: 80 days to maturity, 154 available after May 7. | — |
| Sage | Mar 5 | May 7–May 14 | 168 | fits: 75 days to maturity, 168 available after May 7. | — |
| Thyme | Feb 19 | May 7–May 14 | 168 | fits: 90 days to maturity, 168 available after May 7. | — |
| Calendula | Mar 19 | Apr 16–Apr 30 | 175 | two-plantings: Plant Apr 16 and again by Aug 5; both mature before Oct 8. | Aug 5 |
| Cosmos | Apr 2 | Apr 30–May 14 | 140 | two-plantings: Plant Apr 30 and again by Jul 5; both mature before Sep 17. | Jul 5 |
| Lavender | Feb 5 | Apr 30–May 14 | 175 | fits: 90 days to maturity, 175 available after Apr 30. | — |
| Marigolds | Mar 19 | Apr 30–May 7 | 140 | two-plantings: Plant Apr 30 and again by Jul 15; both mature before Sep 17. | Jul 15 |
| Melons | Apr 16 | May 14–May 21 | 112 | fits: 85 days to maturity, 112 available after May 14. | May 27 |
| Mint | — | Apr 30–May 14 | 175 | fits: 90 days to maturity, 175 available after Apr 30. | — |
| Nasturtiums | Apr 2 | Apr 30–May 7 | 140 | two-plantings: Plant Apr 30 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Pole Beans | — | May 7–May 21 | 133 | fits: 65 days to maturity, 133 available after May 7. | Jun 30 |
| Spaghetti Squash | Apr 16 | May 14–May 21 | 119 | fits: 90 days to maturity, 119 available after May 14. | May 29 |
| Sunflowers | — | Apr 30–May 14 | 140 | fits: 70 days to maturity, 140 available after Apr 30. | Jun 25 |
| Tomatillos | Mar 5 | May 7–May 14 | 119 | fits: 75 days to maturity, 119 available after May 7. | Jun 6 |
| Watermelon | Apr 16 | May 7–May 14 | 119 | fits: 80 days to maturity, 119 available after May 7. | Jun 1 |
| Yellow Squash | Apr 16 | May 14–May 21 | 126 | two-plantings: Plant May 14 and again by Jul 10; both mature before Sep 17. | Jul 10 |
| Zinnias | Apr 2 | Apr 30–May 14 | 140 | two-plantings: Plant Apr 30 and again by Jul 5; both mature before Sep 17. | Jul 5 |
Month by month in Mason City
| Month | What to do |
|---|---|
| January | Plan your garden layout and order seeds. Research varieties suited to your frost dates. |
| February | Start indoors: Chives (Feb 5), Lavender (Feb 5), Onion (Feb 5), Rosemary (Feb 5), Celery (Feb 19), Collards (Feb 19), +5 more. |
| March | Start indoors: Broccoli (Mar 5), Brussel Sprouts (Mar 5), Cabbage (Mar 5), Lettuce (Mar 5), Sage (Mar 5), Swiss Chard (Mar 5), +8 more. Direct sow from: Arugula (Mar 5), Beets (Mar 5), Dill (Mar 5), Peas (Mar 5), Radish (Mar 5), Spinach (Mar 5), +1 more. Plant: Strawberry (Mar 26). |
| April | Start indoors: Bok Choy (Apr 2), Corn (Apr 2), Cosmos (Apr 2), Nasturtiums (Apr 2), Okra (Apr 2), Zinnias (Apr 2), +9 more. Direct sow from: Cilantro (Apr 2), Turnip (Apr 2), Carrots (Apr 9), Potatoes (Apr 16), Sunflowers (Apr 30). Transplant from: Broccoli (Apr 2), Brussel Sprouts (Apr 2), Cabbage (Apr 2), Collards (Apr 2), Kale (Apr 2), Lettuce (Apr 2), +12 more. Last frost around April 30. |
| May | Direct sow from: Beans (May 7), Pole Beans (May 7). Transplant from: Celery (May 7), Chives (May 7), Corn (May 7), Okra (May 7), Oregano (May 7), Parsley (May 7), +17 more. Last sowing dates: Butternut Squash (May 19), Pumpkin (May 19), Cantaloupe (May 27), Celery (May 27), Melons (May 27), Spaghetti Squash (May 29). |
| June | Last sowing dates: Tomato (Jun 1), Watermelon (Jun 1), Pepper (Jun 6), Tomatillos (Jun 6), Eggplant (Jun 11), Corn (Jun 13), +3 more. |
| July | Last sowing dates: Basil (Jul 5), Cosmos (Jul 5), Cucumber (Jul 5), Zinnias (Jul 5), Broccoli (Jul 6), Nasturtiums (Jul 10), +13 more. |
| August | Last sowing dates: Calendula (Aug 5), Cilantro (Aug 5), Collards (Aug 9), Scallions (Aug 9), Bok Choy (Aug 10), Lettuce (Aug 10), +6 more. |
| September | First fall frost approaching (around October 1). Transplant fall brassicas. Sow spinach, arugula, and radishes. |
| October | Direct sow from: Garlic (Oct 1). First frost around October 1. Last sowing dates: Garlic (Oct 22). |
| November | Harvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year. |
| 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 Mason City, IA (ZIP 50401)?
The median last spring frost date for Mason City, IA (ZIP code 50401) is around April 30. 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 16; one in ten it runs past May 13.
What is the first fall frost date in Mason City, IA?
The median first fall frost date for Mason City, IA is around October 1. 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 20 in the earliest one-in-ten years, so cover tomatoes and peppers from then.
How long is the growing season in Mason City, IA?
The frost-free growing season in Mason City is about 154 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 Mason City (154 frost-free days, a moderate season), 32 of 56 planner crops fit outright, 23 get two plantings, 1 crop is perennial.
What USDA hardiness zone is Mason City, IA?
Mason City, IA is in USDA hardiness zone 5a (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 Mason City, IA?
Start tomatoes indoors Mar 26 and plant out May 14 in Mason City. The planner uses the local median last frost and this crop's indoor-start and transplant offsets.
How many plantings of lettuce fit in Mason City?
Two: plant Apr 2 and again by Aug 10; both mature before Oct 8.
When do I plant garlic in Mason City?
Oct 1 to Oct 22; it overwinters and is ready the following summer.
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