When to plant zucchini and summer squash in Walla Walla, WA

Plant zucchini and summer squash in the garden in Walla Walla May 1–29, either as seeds or as young plants started indoors Apr 3–10.

Easy Plant seeds or young plants

Why these dates

Walla Walla's typical last spring frost is March 27. Frost kills zucchini and summer squash, and warm-season crops also need warm soil. Soil here stays cold for weeks after the last frost, so planting waits until about May 1.

Columbia Basin and low eastern valleys. Hot, dry summers and quick spring warm-up. Warm crops go in earlier than west of the Cascades, and irrigation matters more than rain.

Difficulty: Easy
Sun: Full sun
Spacing: 3 feet apart
Planting depth: 1 inch deep
Frost: Killed by frost
First harvest: About 55 days after planting

Step by step

Start seeds indoors Apr 3–10 in trays or small pots under a grow light or in your sunniest window. Or skip this step and buy young plants (starts) at a garden center.
Harden off the young plants: about a week before planting, set them outside for a few hours a day, a little longer each day.
Plant them in the garden May 1–29, 3 feet apart. If you plant seeds instead, sow them 1 inch deep.
Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
Harvest: Pick zucchini at 6 to 8 inches. Miss a few days and you'll have a baseball bat.

Varieties that do well here

Black Beauty
Costata Romanesco
Early Prolific Straightneck

Watch out for

Powdery mildew late in the season. Remove the worst leaves and keep watering at the base.

Two plants feed most families. Pick fruit small and often.

Common questions

When is the last frost in Walla Walla, WA?

Typically March 27. In 9 years out of 10, frost is over by April 22. These are 1991–2020 NOAA climate normals for Walla Walla Regional Airport.

Is it too late to plant zucchini and summer squash in Walla Walla?

The spring planting window runs through May 29. Later plantings may not have time to produce before the first fall frost, which usually arrives around October 31.

When should I start zucchini and summer squash from seed indoors in Walla Walla?

April 3 to April 10, which is 4 to 3 weeks before the May 1 planting date. Or buy young plants at a garden center instead.