When to Plant Sweet Corn in San Mateo County, CA
Top priorities for San Mateo County, California gardeners in May
Each item below is timed to San Mateo County, California's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Start harvesting sweet corn
Morning harvests are best — cooler temperatures mean crisper produce and longer fridge life.
Sweet corn is bred for high sugar content in its kernels, which convert to starch rapidly after harvest. Modern supersweet varieties hold their sweetness longer.
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 Sweet Corn to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Sweet Corn 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.
Soil Compatibility in San Mateo County
How your county's soil matches Sweet Corn's growing requirements.
Soil pH
Your soil pH (6.8–7.2) overlaps with Sweet Corn's range (6.0–7.0), though not a perfect match.
Soil Texture
The loam soil in San Mateo County is excellent for Sweet Corn — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Sweet Corn.
Organic Matter
Organic matter is moderate (2.6%). Annual compost additions will help Sweet Corn.
How to Plant Sweet Corn
Succession Planting Sweet Corn
Sow every 6.9 weeks. Last sowing by Sep 13 to harvest before frost.
Plant Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Sweet Corn
Sweet Corn needs approximately 1.5 inches of water per week (6.5" per month). Here's how your county's rainfall compares month by month.
| Month | Sweet Corn Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | 6.5" | 3.9" | 2.6" | 💧 Light watering |
| Feb | 6.5" | 3.4" | 3.1" | 💧 Light watering |
| Mar | 6.5" | 2.7" | 3.8" | 🚿 Regular watering |
| Apr | 6.5" | 1.2" | 5.3" | 🚿 Regular watering |
| May | 6.5" | 0.4" | 6.1" | 🚿 Regular watering |
| Jun | 6.5" | 0.1" | 6.4" | 🚿 Regular watering |
| Jul | 6.5" | 0" | 6.5" | 🚿 Regular watering |
| Aug | 6.5" | 0" | 6.5" | 🚿 Regular watering |
| Sep | 6.5" | 0.2" | 6.3" | 🚿 Regular watering |
| Oct | 6.5" | 0.7" | 5.8" | 🚿 Regular watering |
| Nov | 6.5" | 1.4" | 5.1" | 🚿 Regular watering |
| Dec | 6.5" | 2.9" | 3.6" | 🚿 Regular watering |
Water needs are for active growing months only (Jan–Dec in San Mateo County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Sweet Corn Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Sweet Corn Planting Timeline — San Mateo County, CA
Sweet Corn Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Direct Sow | January 25 | Jan 25 – Feb 15 |
| Harvest | March 29 | Mar 29 – May 10 |
Plant 1" deep · 12" apart · Rows 36" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Direct Sow |
| February | Direct Sow |
| March | Harvest |
| April | Harvest |
| May | Harvest |
| June | — |
| July | — |
| August | — |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1.5"/week · 2-3 times/week
📅 Days to Maturity
60–90 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 10a
📆 Growing Season
328 days in San Mateo County
Growing Tips for Sweet Corn in San Mateo County
Direct sow Sweet Corn outdoors after January 18 in San Mateo County when soil has warmed and frost danger has passed.
Common pests for Sweet Corn in this region include corn earworm and corn borers. Use row covers early in the season and inspect plants weekly.
San Mateo County receives only 17" of rain annually. Sweet Corn needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Plant in blocks of at least 4 rows for wind pollination. Direct sow after soil is warm. Isolate supersweet varieties from other corn types to prevent cross-pollination.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Sweet Corn in Other Locations
Frequently Asked Questions
When should I plant Sweet Corn in San Mateo County, CA?
San Mateo County is in Zone 10a with an average last frost of January 18. Plan your Sweet Corn 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.
Your San Mateo County Garden Planner — Free
A 24-page printable planner built for San Mateo County (Zone 10a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.