When to Plant Basil in Kauai County, HI
Basil is a fragrant warm-season herb essential to Italian and Thai cuisines. It comes in many varieties including sweet, Thai, purple, and lemon types.
Kauai 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 577 feet, Kauai County receives approximately 89.5 inches of rainfall annually with predominantly silty clay soil. Summer highs average 90°F, providing good warmth for Basil during the growing season. Clay soil retains moisture well for Basil, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Basil root diseases.
Kauai County Soil Profile
Soil Type
Silty Clay
Soil pH
5.5-6.7
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 Kauai County
How your county's soil matches Basil's growing requirements.
Soil pH
Your soil pH (5.5–6.7) overlaps with Basil's range (6.0–7.0), though not a perfect match.
Soil Texture
Your silty clay soil in Kauai County is workable for Basil. Add compost annually to improve structure.
Organic Matter
Organic matter is excellent (4.5%) — Basil will thrive.
How to Plant Basil
Plant Water Budget
Monthly Watering Guide for Basil
Basil needs approximately 0.6 inches of water per week (2.6" per month). Here's how your county's rainfall compares month by month.
| Month | Basil Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | 2.6" | 12.1" | 0" | ✅ Rainfall sufficient |
| Feb | 2.6" | 8.6" | 0" | ✅ Rainfall sufficient |
| Mar | 2.6" | 10.5" | 0" | ✅ Rainfall sufficient |
| Apr | 2.6" | 8.4" | 0" | ✅ Rainfall sufficient |
| May | 2.6" | 5.3" | 0" | ✅ Rainfall sufficient |
| Jun | 2.6" | 2.5" | 0.1" | 💧 Light watering |
| Jul | 2.6" | 2.2" | 0.4" | 💧 Light watering |
| Aug | 2.6" | 3.1" | 0" | ✅ Rainfall sufficient |
| Sep | 2.6" | 4.3" | 0" | ✅ Rainfall sufficient |
| Oct | 2.6" | 9.8" | 0" | ✅ Rainfall sufficient |
| Nov | 2.6" | 9.3" | 0" | ✅ Rainfall sufficient |
| Dec | 2.6" | 13.3" | 0" | ✅ Rainfall sufficient |
Water needs are for active growing months only (Jan–Dec in Kauai County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Basil 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.
Basil Planting Timeline — Kauai County, HI
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | November 20 | Nov 20 – Dec 4 |
| Transplant Outdoors | January 8 | Jan 8 – Jan 22 |
| Direct Sow | January 8 | Jan 8 – Jan 29 |
| Harvest | March 5 | Mar 5 – May 7 |
Plant 0.5" deep · 8" apart · Rows 12" 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 | Start Indoors |
| December | Start Indoors |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.6"/week · Natural rainfall sufficient
📅 Days to Maturity
50–75 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 11a
📆 Growing Season
364 days in Kauai County
Growing Tips for Basil in Kauai County
With Kauai County's clay soil (31% clay), work in 3-4 inches of compost before planting Basil. Avoid tilling when soil is wet to prevent compaction.
General growing tips
Start seeds indoors or direct sow after last frost. Pinch flower buds to extend leaf production. Harvest leaves from the top down, cutting just above a leaf pair.
Recommended Basil Varieties for Kauai County
Downy mildew-resistant basil for your humid climate
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Isolate 150 ft between varieties. Different basil species can cross.
Basil in Other Locations
Frequently Asked Questions
When should I plant Basil in Kauai County, HI?
Kauai County is in Zone 11a with an average last frost of January 1. Plan your Basil planting based on this frost date — see the calendar above for exact timing.
What planting zone is Kauai County, HI?
Kauai 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 Kauai County gardeners in Zone 11a organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.