When to Plant Sunflower in Kalawao County, HI
What to do in May
Your Kalawao County, Hawaii garden is entering a new phase. Here's what's on the schedule for May and why each task matters now.
Sunflowers are tall, cheerful annuals grown for their edible seeds and as pollinator magnets. They come in sizes from 2-foot dwarfs to 12-foot 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 Sunflower during the growing season. Clay soil retains moisture well for Sunflower, 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 Sunflower's growing requirements.
Soil pH
Your soil pH (5.7–6.7) overlaps with Sunflower's range (6.0–7.5), though not a perfect match.
Soil Texture
Your silty clay soil in Kalawao County is workable for Sunflower. Add compost annually to improve structure.
Organic Matter
Organic matter is moderate (3.9%). Annual compost additions will help Sunflower.
How to Plant Sunflower
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Sunflower
Sunflower needs approximately 0.5 inches of water per week (2.2" per month). Here's how your county's rainfall compares month by month.
| Month | Sunflower Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | 2.2" | 4.1" | 0" | ✅ Rainfall sufficient |
| Feb | 2.2" | 3.1" | 0" | ✅ Rainfall sufficient |
| Mar | 2.2" | 3.4" | 0" | ✅ Rainfall sufficient |
| Apr | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 1.6" | 0.6" | 💧 Light watering |
| Jun | 2.2" | 0.9" | 1.3" | 🚿 Regular watering |
| Jul | 2.2" | 0.7" | 1.5" | 🚿 Regular watering |
| Aug | 2.2" | 0.9" | 1.3" | 🚿 Regular watering |
| Sep | 2.2" | 1.4" | 0.8" | 💧 Light watering |
| Oct | 2.2" | 2.8" | 0" | ✅ Rainfall sufficient |
| Nov | 2.2" | 2.9" | 0" | ✅ Rainfall sufficient |
| Dec | 2.2" | 4" | 0" | ✅ Rainfall sufficient |
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.
Sunflower 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.
Sunflower Planting Timeline — Kalawao County, HI
Sunflower 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 1 | Jan 1 – Jan 22 |
| Harvest | March 19 | Mar 19 – May 7 |
Plant 1" deep · 18" apart · Rows 30" 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
0.5"/week · Only during dry spells
📅 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 Sunflower in Kalawao County
With Kalawao County's clay soil (37% clay), work in 3-4 inches of compost before planting Sunflower. Avoid tilling when soil is wet to prevent compaction.
Common pests for Sunflower in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Direct sow after last frost. Stake tall varieties in windy areas. Harvest seed heads when the back turns brown and seeds are plump. Dry heads upside down.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Sunflower in Other Locations
Frequently Asked Questions
When should I plant Sunflower in Kalawao County, HI?
Kalawao County is in Zone 11a with an average last frost of January 1. Plan your Sunflower 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.
Your Kalawao County Garden Planner — Free
A 24-page printable planner built for Kalawao County (Zone 11a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.