Frost Dates for Kennewick, WA 99338

Kennewick has 3 ZIP codes. The Kennewick, WA frost page lists all of them with their dates.

Last spring frost April 7 · First fall frost October 21 · 197 frost-free days · USDA Zone 7b

Frost probability for 99338

Frost10%50%90%
Spring (last frost)April 21April 7March 18
Fall (first frost)October 5October 21November 6

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (15.4 km away); the 50% date is the median year.

Month by month in Kennewick

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart peppers and eggplant indoors 8–10 weeks before your last frost (around April 7). Start tomatoes about two weeks later, 6–8 weeks before last frost.
MarchStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
AprilLast frost around April 7. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
MayFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
JuneSuccession plant lettuce and greens. Keep beds weeded and watered consistently.
JulyHarvest regularly to encourage production. Monitor for pests and disease.
AugustMidsummer: harvest beans, zucchini, cucumbers. Start brassica seeds indoors for fall.
SeptemberFirst fall frost approaching (around October 21). Transplant fall brassicas. Sow spinach, arugula, and radishes.
OctoberFirst frost around October 21. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
NovemberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 197-day season

Frequently Asked Questions

What is the last frost date for Kennewick, WA (ZIP 99338)?

The median last spring frost date for Kennewick, WA (ZIP code 99338) is around April 7. 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.

What is the first fall frost date in Kennewick, WA?

The median first fall frost date for Kennewick, WA is around October 21. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Kennewick, WA?

The frost-free growing season in Kennewick is about 197 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.

What USDA hardiness zone is Kennewick, WA?

Based on frost date patterns, Kennewick falls approximately in 7b. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Kennewick, WA?

Start tomato seeds indoors 6–8 weeks before your last frost date (around April 7). For Kennewick, that's roughly February 11 to February 25. Transplant outdoors 1–2 weeks after your last frost.

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