Frost Dates for Castro Valley, CA 94552

Castro Valley has 2 ZIP codes. The Castro Valley, CA frost page lists all of them with their dates.

Last spring frost March 13 · First fall frost November 24 · 256 frost-free days · USDA Zone 9b

Frost probability for 94552

Frost10%50%90%
Spring (last frost)April 7March 13January 18
Fall (first frost)November 12November 24January 14

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (20.7 km away); the 50% date is the median year.

Month by month in Castro Valley

MonthWhat to do
JanuaryStart peppers and eggplant indoors 8–10 weeks before your last frost (around March 13). Start tomatoes about two weeks later, 6–8 weeks before last frost.
FebruaryStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
MarchLast frost around March 13. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
AprilFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
MaySuccession plant lettuce and greens. Keep beds weeded and watered consistently.
JuneHarvest regularly to encourage production. Monitor for pests and disease.
JulyMidsummer: harvest beans, zucchini, cucumbers. Start brassica seeds indoors for fall.
AugustDirect sow carrots and beets for fall harvest. Start fall broccoli and kale indoors.
SeptemberDirect sow carrots and beets for fall harvest. Start fall broccoli and kale indoors.
OctoberFirst fall frost approaching (around November 24). Transplant fall brassicas. Sow spinach, arugula, and radishes.
NovemberFirst frost around November 24. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
DecemberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.

What grows in a 256-day season

Frequently Asked Questions

What is the last frost date for Castro Valley, CA (ZIP 94552)?

The median last spring frost date for Castro Valley, CA (ZIP code 94552) is around March 13. 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 Castro Valley, CA?

The median first fall frost date for Castro Valley, CA is around November 24. 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 Castro Valley, CA?

The frost-free growing season in Castro Valley is about 256 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 Castro Valley, CA?

Based on frost date patterns, Castro Valley falls approximately in 9b. 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 Castro Valley, CA?

Start tomato seeds indoors 6–8 weeks before your last frost date (around March 13). For Castro Valley, that's roughly January 17 to January 31. Transplant outdoors 1–2 weeks after your last frost.

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