When to Plant Watermelon in San Bernardino County, CA
May to-do list for San Bernardino County, California
We've pulled the most time-sensitive tasks for San Bernardino County, California this May and put them front and centre. Tackle them in order.
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Basket week: watermelon
Taste as you pick. The first ripe produce is the best feedback loop you'll get all season.
Before June arrives, get these ready
- First harvests: watermelon
Watermelon is a sprawling vine crop that produces sweet, juicy fruits in hot weather. Varieties range from personal-sized icebox types to 50-pound giants.
San Bernardino County, California is in USDA Zone 10a. The average last spring frost is February 24 and the first fall frost is November 25, giving you a growing season of approximately 274 days.
At an elevation of 1,012 feet, San Bernardino County receives approximately 16.9 inches of rainfall annually with predominantly loam soil. Summer highs average 97°F, so Watermelon may need afternoon shade and extra watering during peak heat. With low rainfall, drip irrigation is essential for growing Watermelon successfully. Mulch heavily to conserve soil moisture.
San Bernardino County Soil Profile
Soil Type
Loam
Soil pH
5.9-7.2
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 Bernardino County
How your county's soil matches Watermelon's growing requirements.
Soil pH
Your soil pH (5.9–7.2) overlaps with Watermelon's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in San Bernardino County is excellent for Watermelon — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.4%). Annual compost additions will help Watermelon.
How to Plant Watermelon
Succession Planting Watermelon
Sow every 8 weeks. Last sowing by Aug 17 to harvest before frost.
Plant Water Budget
Water stress score is 10/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Watermelon
Watermelon 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 | Watermelon Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 3.2" | 0" | ❄️ Dormant |
| Feb | 6.5" | 3.8" | 2.7" | 💧 Light watering |
| Mar | 6.5" | 2.2" | 4.3" | 🚿 Regular watering |
| Apr | 6.5" | 1.5" | 5" | 🚿 Regular watering |
| May | 6.5" | 0.5" | 6" | 🚿 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" | 1.7" | 4.8" | 🚿 Regular watering |
| Dec | — | 3" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in San Bernardino County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Watermelon 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.
Watermelon Planting Timeline — San Bernardino County, CA
Watermelon Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | January 27 | Jan 27 – Feb 10 |
| Transplant Outdoors | March 3 | Mar 3 – Mar 17 |
| Direct Sow | February 24 | Feb 24 – Mar 17 |
| Harvest | May 12 | May 12 – Jun 30 |
Plant 1" deep · 30" apart · Rows 42" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Start Indoors |
| February | Start Indoors Direct Sow |
| March | Transplant Outdoors Direct Sow |
| April | — |
| May | Harvest |
| June | Harvest |
| 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
70–100 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 10a
📆 Growing Season
274 days in San Bernardino County
Growing Tips for Watermelon in San Bernardino County
Direct sow Watermelon outdoors after February 24 in San Bernardino County when soil has warmed and frost danger has passed.
With summer highs reaching 97°F in San Bernardino County, provide afternoon shade for Watermelon and water deeply in the morning.
Common pests for Watermelon in this region include squash vine borer and cucumber beetles. Use row covers early in the season and inspect plants weekly.
San Bernardino County receives only 17" of rain annually. Watermelon needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Start seeds indoors 3-4 weeks early or direct sow after soil is warm. Plant on mounds with plenty of space. Check ripeness by looking for a yellow ground spot and dull thump when tapped.
Recommended Watermelon Varieties for San Bernardino County
Full-size melons that thrive with your long season
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Watermelon in Other Locations
Frequently Asked Questions
When should I plant Watermelon in San Bernardino County, CA?
San Bernardino County is in Zone 10a with an average last frost of February 24. Plan your Watermelon planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Bernardino County, CA?
San Bernardino County, California is in USDA Hardiness Zone 10a. The average last spring frost is February 24 and first fall frost is November 25.
Your San Bernardino County Garden Planner — Free
A 24-page printable planner built for San Bernardino 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.