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Caldwell, Idaho planting calendar and frost dates

Caldwell is in USDA hardiness zone 7a. The last spring frost typically comes around April 29 and the first fall frost around October 13, giving about 164 frost-free days a year.

Hardiness zone
Zone 7a
Typical last frost
April 29
Typical first frost
October 13
Frost-free season
164 days

Frost dates in Caldwell

Last spring frost

  • April 15Risky: frost later than this in 9 years out of 10
  • April 29Typical: a later frost in half of years
  • May 18Safe: a later frost only 1 year in 10

First fall frost

  • September 29Risky: frost earlier than this 1 year in 10
  • October 13Typical: an earlier frost in half of years
  • October 28Late: frost before this in 9 years out of 10

The growing season between the typical last and first frosts is about 164 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 11 and returns around October 25.

NOAA U.S. Climate Normals 1991-2020 for Nampa Sugar Factory, 5.6 miles SE of the city center. 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 Caldwell

  1. January

    Start indoors: onions

  2. February

    Start indoors: broccoli, cabbages, cauliflower, collard greens, kale, leeks, onions, oregano, parsley, petunias, ranunculus, rosemary, snapdragons

  3. 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: black-eyed susans, blueberries, garlic, grapes, grass seed, hollyhocks, kale, onions, peas, poppies, raspberries, rhubarb, strawberries, turnips, wildflowers

  4. April

    Start indoors: basil, cantaloupes, cilantro, cosmos, cucumbers, marigolds, nasturtiums, okra, pumpkins, ranunculus, tomatoes, watermelons, winter squash, zucchini

    Plant or sow outdoors: asparagus, beets, black-eyed susans, blackberries, blueberries, broccoli, cabbages, carrots, cauliflower, chives, cilantro, collard greens, dahlias, dill, figs, garden mums, garlic, gladioli, grapes, grass seed, green onions, hollyhocks, kale, lavenders, leeks, lettuce, lilies, marigolds, mints, nasturtiums, onions, oregano, parsley, peas, petunias, poppies, potatoes, radishes, ranunculus, raspberries, rhubarb, rosemary, roses, sage, snapdragons, spinach, strawberries, sunflowers, sweet corn, swiss chard, thyme, turnips, wildflowers

  5. 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, sunflowers, sweet corn, sweet peas, swiss chard, tall fescue, thyme, tomatoes, watermelons, winter squash, zucchini

  6. June

    Start indoors: zinnias

    Plant or sow outdoors: 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

  7. July

    Plant or sow outdoors: bermudagrass, centipedegrass, st. augustinegrass, zinnias, zoysiagrass

    Plant for fall: bearded irises, broccoli, brussels sprouts, carrots, collard greens, lettuce, peas, snapdragons, swiss chard

  8. 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

  9. 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

  10. October

    Plant for fall: crocuses, daffodils, garlic, hyacinths, lilies, ornamental alliums, peonies, tulips

Frost dates and zones by ZIP code in Caldwell

Caldwell's 3 main ZIP codes take their frost dates from 3 different NOAA stations: the typical last frost ranges from April 23 in 83607 to April 29 in 83605. Every one of them is in zone 7a.

ZIP codeZoneWeather stationTypical last frostTypical first frost
836057aNampa Sugar Factory, 5.6 mi SEApr 29Oct 13
836077aDeer Flat Dam, 9.3 mi SApr 23Oct 18
836877aBoise Air Terminal, 3.7 mi SSWApr 24Oct 21

Planting dates for popular crops in Caldwell

PlantStart indoorsPlant or sow outdoorsFall planting
TomatoesMar 24 to Apr 7May 19 to Jun 2—
Strawberries—Mar 18 to Apr 1—
LettuceMar 4 to 18Apr 22 to May 6Jul 14 to Aug 18
CilantroMar 18 to Apr 1Apr 29 to May 6—
BasilMar 31 to Apr 14May 19 to 26—
Potatoes—Apr 16 to 23—
Garlic—Mar 18 to Apr 1Oct 13 to 27
OnionsJan 7 to Feb 18Apr 1 to 15—
CucumbersApr 21 to May 5May 19 to Jun 2—
PumpkinsApr 21 to May 5May 19 to Jun 2—
PeppersMar 3 to 31May 19 to Jun 2—
Carrots—Apr 8 to 29Jul 21 to Aug 11
Sweet Potatoes—Jun 9 to 16—
WatermelonsApr 14 to 28May 19 to Jun 2—
Sweet Corn—Apr 29 to May 13—
Green Beans—May 19 to Jun 2—
ZucchiniApr 21 to May 5May 19 to Jun 2—
BroccoliFeb 11 to Mar 4Apr 1 to 15Jul 28 to Aug 25
Peas—Mar 18 to Apr 1Jul 21 to Aug 4
SpinachMar 18 to 25Apr 22 to May 6Aug 4 to Sep 8
Sunflowers—Apr 29 to May 20—
ZinniasMay 30 to Jun 6Jun 27 to Jul 11—
Tulips——Sep 1 to Oct 27
Daffodils——Sep 1 to Oct 13
Grass Seed—Mar 18 to Apr 1Sep 1 to 15

Nearby cities

Planting in IdahoAbout zone 7aPrintable calendar for Caldwell

Questions

When is the last frost in Caldwell?

Around April 29 in a typical year, based on NOAA's 1991-2020 records for Nampa Sugar Factory. There is still a 1 in 10 chance of frost after May 18.

What planting zone is Caldwell in?

USDA hardiness zone 7a (2023 map). The zone tells you which perennials survive the winter; planting dates depend on frost dates instead.

When should I plant tomatoes in Caldwell?

Start seeds indoors March 24 to April 7 and set plants out May 19 to June 2.

When is the first frost in Caldwell?

Around October 13 in a typical year, and before September 29 about 1 year in 10.