When to Plant Yam in Hawaii County, HI
Your May gardening checklist
May rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Hawaii County, Hawaii.
True yams are tropical tubers distinct from sweet potatoes, producing large starchy roots that can weigh several pounds. They are a staple food in tropical regions worldwide.
Hawaii County, Hawaii is in USDA Zone 12b. 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 525 feet, Hawaii County receives approximately 96.2 inches of rainfall annually with predominantly silty clay soil. Summer highs average 87°F, providing good warmth for Yam during the growing season. Clay soil retains moisture well for Yam, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Yam root diseases.
Hawaii County Soil Profile
Soil Type
Silty Clay
Soil pH
5.6-6.6
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 Hawaii County
How your county's soil matches Yam's growing requirements.
Soil pH
Your soil pH (5.6–6.6) overlaps with Yam's range (5.5–6.5), though not a perfect match.
Soil Texture
Your silty clay soil in Hawaii County is workable for Yam. Add compost annually to improve structure.
Organic Matter
Organic matter is excellent (4.1%) — Yam will thrive.
How to Plant Yam
Plant Water Budget
Monthly Watering Guide for Yam
Yam needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Yam Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | 4.3" | 13.1" | 0" | ✅ Rainfall sufficient |
| Feb | 4.3" | 11.1" | 0" | ✅ Rainfall sufficient |
| Mar | 4.3" | 11.1" | 0" | ✅ Rainfall sufficient |
| Apr | 4.3" | 8.4" | 0" | ✅ Rainfall sufficient |
| May | 4.3" | 5.6" | 0" | ✅ Rainfall sufficient |
| Jun | 4.3" | 2.5" | 1.8" | 💧 Light watering |
| Jul | 4.3" | 2.3" | 2" | 💧 Light watering |
| Aug | 4.3" | 2.7" | 1.6" | 💧 Light watering |
| Sep | 4.3" | 4.7" | 0" | ✅ Rainfall sufficient |
| Oct | 4.3" | 10.3" | 0" | ✅ Rainfall sufficient |
| Nov | 4.3" | 12.3" | 0" | ✅ Rainfall sufficient |
| Dec | 4.3" | 12" | 0" | ✅ Rainfall sufficient |
Water needs are for active growing months only (Jan–Dec in Hawaii County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Yam 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.
Yam Planting Timeline — Hawaii County, HI
Yam 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 | July 9 | Jul 9 – Dec 24 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | — |
| March | — |
| April | — |
| May | — |
| June | — |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | Start Indoors Harvest |
| December | Start Indoors Harvest |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Natural rainfall sufficient
📅 Days to Maturity
180–330 days
🧪 Soil pH
Needs 5.5–6.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 12b
📆 Growing Season
364 days in Hawaii County
Growing Tips for Yam in Hawaii County
With Hawaii County's clay soil (39% clay), work in 3-4 inches of compost before planting Yam. Avoid tilling when soil is wet to prevent compaction.
General growing tips
Plant tuber pieces in mounds of loose, rich soil. Provide sturdy trellising for climbing vines. Yams require a long, warm growing season of 8-11 months. Harvest when vines die back.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Yam in Other Locations
Frequently Asked Questions
When should I plant Yam in Hawaii County, HI?
Hawaii County is in Zone 12b with an average last frost of January 1. Plan your Yam planting based on this frost date — see the calendar above for exact timing.
What planting zone is Hawaii County, HI?
Hawaii County, Hawaii is in USDA Hardiness Zone 12b. The average last spring frost is January 1 and first fall frost is December 31.
Your Hawaii County Garden Planner — Free
A 24-page printable planner built for Hawaii County (Zone 12b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.