Frost Dates for Castro Valley, CA 94546
Last spring frost Frost-free zone · First fall frost Frost-free zone · 365 frost-free days · USDA Zone 9b
Frost probability for 94546
| Frost | 10% | 50% | 90% |
|---|---|---|---|
| Spring (last frost) | January 18 | — | — |
| Fall (first frost) | December 25 | — | — |
Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (16.8 km away); the 50% date is the median year.
Frost dates by ZIP code in Castro Valley, CA
| ZIP | Last spring frost (50%) | First fall frost (50%) | Zone |
|---|---|---|---|
| 94546 | — | — | 9b |
| 94552 | March 13 | November 24 | 9b |
Month by month in Castro Valley
| Month | What to do |
|---|---|
| January | Plant cool-season crops: lettuce, spinach, broccoli, peas, and carrots. |
| February | Direct sow brassicas and root vegetables. Start warm-season seedlings indoors. |
| March | Transplant warm-season crops outdoors. Sow beans, cucumbers, and squash. |
| April | Main warm-season planting window. Direct sow melons and sweet corn. |
| May | Succession plant lettuce. Keep beds irrigated as temperatures climb. |
| June | Monitor for heat stress. Harvest zucchini and cucumbers frequently. |
| July | Harvest regularly to encourage continued production. Watch for pests. |
| August | Start fall cool-season crops: broccoli, kale, beets, and carrots. |
| September | Plant fall lettuce, spinach, arugula, and radishes. |
| October | Harvest mature crops. Direct sow cold-tolerant greens. |
| November | Plant garlic and onion sets. Harvest cool-season crops through the month. |
| December | Plant cool-season crops for winter harvest. Plan next year's garden. |
What grows in a 365-day season
Frequently Asked Questions
What is the last frost date for Castro Valley, CA (ZIP 94546)?
Castro Valley, CA is frost-free in most years, so there's no last spring frost date to plan around.
What is the first fall frost date in Castro Valley, CA?
Castro Valley, CA is frost-free in most years, so there's no first fall frost date to plan around.
How long is the growing season in Castro Valley, CA?
The frost-free growing season in Castro Valley is year-round. 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?
Castro Valley is a frost-free zone, so you can start tomatoes and transplant at any time of year. Focus on heat management rather than frost timing.
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