When to Plant Amaranth in San Mateo County, CA
Amaranth is an ancient grain crop with edible leaves and seeds, rich in protein and micronutrients. It thrives in warm conditions and is drought-tolerant once established.
San Mateo County, California is in USDA Zone 10a. The average last spring frost is January 18 and the first fall frost is December 12, giving you a growing season of approximately 328 days.
At an elevation of 277 feet, San Mateo County receives approximately 16.9 inches of rainfall annually with predominantly loam soil. Summer highs average 81°F, so choose short-season varieties of Amaranth to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Amaranth successfully. Mulch heavily to conserve soil moisture.
San Mateo County Soil Profile
Soil Type
Loam
Soil pH
6.8-7.2
Drainage
Well Drained
Plant Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Plant Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Amaranth Planting Timeline — San Mateo County, CA
Amaranth Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | December 7 | Dec 7 – Dec 21 |
| Transplant Outdoors | January 25 | Jan 25 – Feb 8 |
| Direct Sow | January 18 | Jan 18 – Feb 8 |
| Harvest | April 26 | Apr 26 – Jun 14 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | Transplant Outdoors Direct Sow |
| March | — |
| April | Harvest |
| May | Harvest |
| June | Harvest |
| July | — |
| August | — |
| September | — |
| October | — |
| November | — |
| December | Start Indoors |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7.5
USDA Zone
Zone 10a
Growing Season
328 days
Growing Tips for San Mateo County
Direct sow after last frost when soil is warm. Thin seedlings to 18 inches apart. Harvest leaves when young and tender; harvest seeds when flower heads begin to dry.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Amaranth in Other Locations
Frequently Asked Questions
When should I plant Amaranth in San Mateo County, CA?
San Mateo County is in Zone 10a with an average last frost of January 18. Plan your Amaranth planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Mateo County, CA?
San Mateo County, California is in USDA Hardiness Zone 10a. The average last spring frost is January 18 and first fall frost is December 12.
Plan Your Garden with Confidence
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