When to Plant Watermelon in Kalawao County, HI
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.
Kalawao County, Hawaii is in USDA Zone 11a. The average last spring frost is January 1 and the first fall frost is December 31, giving you a growing season of approximately 364 days.
At an elevation of 402 feet, Kalawao County receives approximately 28.4 inches of rainfall annually with predominantly silty clay soil. Summer highs average 85°F, providing good warmth for Watermelon during the growing season. Clay soil retains moisture well for Watermelon, but amend with compost to improve drainage and prevent root rot.
Kalawao County Soil Profile
Soil Type
Silty Clay
Soil pH
5.7-6.7
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 Kalawao County
How your county's soil matches Watermelon's growing requirements.
Soil pH
Your soil pH (5.7–6.7) overlaps with Watermelon's range (6.0–7.5), though not a perfect match.
Soil Texture
Your silty clay soil in Kalawao County is workable for Watermelon. Add compost annually to improve structure.
Organic Matter
Organic matter is moderate (3.9%). Annual compost additions will help Watermelon.
How to Plant Watermelon
How Much Watermelon to Grow
For a family of 4, plant approximately 4 watermelon plants in about 35 sq ft. In Kalawao County's 364-day season, you'll have plenty of time for a full harvest. Plan your garden layout →
Plant Water Budget
Water stress score is 6/10 — 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 | 6.5" | 4.1" | 2.4" | 💧 Light watering |
| Feb | 6.5" | 3.1" | 3.4" | 🚿 Regular watering |
| Mar | 6.5" | 3.4" | 3.1" | 💧 Light watering |
| Apr | 6.5" | 2.6" | 3.9" | 🚿 Regular watering |
| May | 6.5" | 1.6" | 4.9" | 🚿 Regular watering |
| Jun | 6.5" | 0.9" | 5.6" | 🚿 Regular watering |
| Jul | 6.5" | 0.7" | 5.8" | 🚿 Regular watering |
| Aug | 6.5" | 0.9" | 5.6" | 🚿 Regular watering |
| Sep | 6.5" | 1.4" | 5.1" | 🚿 Regular watering |
| Oct | 6.5" | 2.8" | 3.7" | 🚿 Regular watering |
| Nov | 6.5" | 2.9" | 3.6" | 🚿 Regular watering |
| Dec | 6.5" | 4" | 2.5" | 💧 Light watering |
Water needs are for active growing months only (Jan–Dec in Kalawao 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 — Kalawao County, HI
Watermelon Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | December 4 | Dec 4 – Dec 18 |
| Transplant Outdoors | January 8 | Jan 8 – Jan 22 |
| Direct Sow | January 1 | Jan 1 – Jan 22 |
| Harvest | March 19 | Mar 19 – May 7 |
Plant 1" deep · 30" apart · Rows 42" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | — |
| March | Harvest |
| April | Harvest |
| May | Harvest |
| June | — |
| July | — |
| August | — |
| September | — |
| October | — |
| November | — |
| December | Start Indoors |
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 11a
📆 Growing Season
364 days in Kalawao County
Growing Tips for Watermelon in Kalawao County
With Kalawao County's clay soil (37% clay), work in 3-4 inches of compost before planting Watermelon. Avoid tilling when soil is wet to prevent compaction.
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.
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 Kalawao 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 Kalawao County, HI?
Kalawao County is in Zone 11a with an average last frost of January 1. Plan your Watermelon planting based on this frost date — see the calendar above for exact timing.
What planting zone is Kalawao County, HI?
Kalawao County, Hawaii is in USDA Hardiness Zone 11a. The average last spring frost is January 1 and first fall frost is December 31.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Kalawao County gardeners in Zone 11a organize planting dates, track what's growing, and never miss a planting window.
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