Janesville, Wisconsin planting calendar and frost dates
Janesville is in USDA hardiness zone 5b. The last spring frost typically comes around April 26 and the first fall frost around October 15, giving about 170 frost-free days a year.
- Hardiness zone
- Zone 5b
- Typical last frost
- April 26
- Typical first frost
- October 15
- Frost-free season
- 170 days
Frost dates in Janesville
Last spring frost
- April 13Risky: frost later than this in 9 years out of 10
- April 26Typical: a later frost in half of years
- May 11Safe: a later frost only 1 year in 10
First fall frost
- October 1Risky: frost earlier than this 1 year in 10
- October 15Typical: an earlier frost in half of years
- October 27Late: frost before this in 9 years out of 10
The growing season between the typical last and first frosts is about 170 days. Frost here means a low of 32°F at the weather station. A hard freeze (28°F), which damages most hardy crops too, typically ends around April 15 and returns around October 26.
NOAA U.S. Climate Normals 1991-2020 for Afton - Janesville Wwtp, 6 miles W of the city center and 142 feet lower. Low-lying and rural spots often frost later in spring and earlier in fall than airports and city centers.
What to plant each month in Janesville
January
Start indoors: onions
February
Start indoors: broccoli, cabbages, cauliflower, collard greens, kale, leeks, onions, oregano, parsley, petunias, ranunculus, rosemary, snapdragons
March
Start indoors: basil, black-eyed susans, broccoli, cabbages, cauliflower, celery, chives, cilantro, collard greens, eggplants, ginger, leeks, lettuce, marigolds, nasturtiums, oregano, parsley, peppers, petunias, ranunculus, rosemary, sage, snapdragons, spinach, swiss chard, tomatoes
Plant or sow outdoors: beets, black-eyed susans, blackberries, blueberries, broccoli, cauliflower, chives, cilantro, collard greens, figs, garlic, gladioli, grapes, grass seed, hollyhocks, kale, leeks, onions, peas, poppies, radishes, ranunculus, raspberries, rhubarb, roses, spinach, strawberries, swiss chard, turnips, wildflowers
April
Start indoors: basil, cantaloupes, cosmos, cucumbers, okra, pumpkins, ranunculus, tomatoes, watermelons, winter squash, zucchini
Plant or sow outdoors: asparagus, beets, black-eyed susans, blackberries, broccoli, cabbages, carrots, cauliflower, chives, cilantro, collard greens, dahlias, dill, figs, garden mums, gladioli, grapes, green onions, lavenders, leeks, lettuce, lilies, marigolds, mints, nasturtiums, onions, oregano, parsley, petunias, potatoes, radishes, ranunculus, rosemary, roses, sage, snapdragons, spinach, sunflowers, sweet corn, swiss chard, thyme, turnips
May
Start indoors: cosmos, cucumbers, okra, pumpkins, winter squash, zinnias, zucchini
Plant or sow outdoors: asparagus, basil, cantaloupes, chives, cilantro, cucumbers, dahlias, dill, eggplants, garden mums, ginger, gladioli, grapes, green beans, green onions, kentucky bluegrass, lavenders, lettuce, lilies, marigolds, mints, nasturtiums, oregano, parsley, peppers, perennial ryegrass, petunias, pumpkins, ranunculus, rosemary, sage, spinach, st. augustinegrass, sunflowers, sweet corn, sweet peas, swiss chard, tall fescue, thyme, tomatoes, watermelons, winter squash, zucchini
June
Plant or sow outdoors: asparagus, bermudagrass, cantaloupes, celery, centipedegrass, cosmos, cucumbers, eggplants, green beans, green onions, okra, peanuts, peppers, pumpkins, st. augustinegrass, sweet potatoes, tomatoes, watermelons, winter squash, zinnias, zoysiagrass, zucchini
July
Plant or sow outdoors: bermudagrass, centipedegrass, green onions, st. augustinegrass, zinnias, zoysiagrass
Plant for fall: bearded irises, broccoli, brussels sprouts, carrots, collard greens, lettuce, peas, snapdragons, swiss chard
August
Plant for fall: azaleas, bearded irises, beets, broccoli, cabbages, carrots, cauliflower, clematis, collard greens, coneflowers, daylilies, hostas, hydrangeas, kale, lettuce, peas, radishes, roses, saffron, snapdragons, spinach, swiss chard, turnips
September
Plant for fall: azaleas, bearded irises, cabbages, cauliflower, clematis, coneflowers, crocuses, daffodils, daylilies, grass seed, hostas, hyacinths, hydrangeas, kale, lilies, ornamental alliums, peonies, radishes, roses, saffron, spinach, tulips
October
Plant for fall: crocuses, daffodils, garlic, hyacinths, lilies, ornamental alliums, peonies, tulips
Frost dates and zones by ZIP code in Janesville
Janesville's 4 main ZIP codes take their frost dates from 2 different NOAA stations: the typical last frost ranges from April 26 in 53545 to April 28 in 53563. Every one of them is in zone 5b.
Planting dates for popular crops in Janesville
| Plant | Start indoors | Plant or sow outdoors | Fall planting |
|---|---|---|---|
| Tomatoes | Mar 24 to Apr 7 | May 19 to Jun 2 | — |
| Strawberries | — | Mar 15 to 29 | — |
| Lettuce | Mar 1 to 15 | Apr 19 to May 3 | Jul 16 to Aug 20 |
| Cilantro | Mar 15 to 29 | Apr 26 to May 3 | — |
| Basil | Mar 31 to Apr 14 | May 19 to 26 | — |
| Potatoes | — | Apr 23 to 30 | — |
| Garlic | — | Mar 15 to 29 | Oct 15 to 29 |
| Onions | Jan 4 to Feb 15 | Mar 29 to Apr 12 | — |
| Cucumbers | Apr 21 to May 5 | May 19 to Jun 2 | — |
| Pumpkins | Apr 21 to May 5 | May 19 to Jun 2 | — |
| Peppers | Mar 3 to 31 | May 19 to Jun 2 | — |
| Carrots | — | Apr 5 to 26 | Jul 23 to Aug 13 |
| Sweet Potatoes | — | Jun 2 to 9 | — |
| Watermelons | Apr 14 to 28 | May 19 to Jun 2 | — |
| Sweet Corn | — | Apr 26 to May 10 | — |
| Green Beans | — | May 19 to Jun 2 | — |
| Zucchini | Apr 21 to May 5 | May 19 to Jun 2 | — |
| Broccoli | Feb 8 to Mar 1 | Mar 29 to Apr 12 | Jul 30 to Aug 27 |
| Peas | — | Mar 15 to 29 | Jul 23 to Aug 6 |
| Spinach | Mar 15 to 22 | Apr 19 to May 3 | Aug 6 to Sep 10 |
| Sunflowers | — | Apr 26 to May 17 | — |
| Zinnias | May 22 to 29 | Jun 19 to Jul 3 | — |
| Tulips | — | — | Sep 3 to Oct 29 |
| Daffodils | — | — | Sep 3 to Oct 15 |
| Grass Seed | — | Mar 15 to 29 | Sep 3 to 17 |
Nearby cities
- Rockford, IL zone 5b, last frost Apr 24
- Madison, WI zone 5b, last frost May 1
- Waukesha, WI zone 5b, last frost May 1
- West Allis, WI zone 5b, last frost Apr 19
- Elgin, IL zone 5b, last frost Apr 26
- Kenosha, WI zone 5b, last frost Apr 28
Planting in WisconsinAbout zone 5bPrintable calendar for Janesville
Questions
When is the last frost in Janesville?
Around April 26 in a typical year, based on NOAA's 1991-2020 records for Afton - Janesville Wwtp. There is still a 1 in 10 chance of frost after May 11.
What planting zone is Janesville in?
USDA hardiness zone 5b (2023 map). The zone tells you which perennials survive the winter; planting dates depend on frost dates instead.
When should I plant tomatoes in Janesville?
Start seeds indoors March 24 to April 7 and set plants out May 19 to June 2.
When is the first frost in Janesville?
Around October 15 in a typical year, and before October 1 about 1 year in 10.