When to Plant Mizuna in Hawaii County, HI
Your April gardening checklist
Your garden in Hawaii County, Hawaii is working on a schedule, even when you're not. Here's where you should be this April.
Mizuna is a mild-flavored Japanese mustard green with feathery, deeply serrated leaves. It is fast-growing and makes an excellent addition to salads and stir-fries.
Hawaii 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 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 Mizuna during the growing season. Clay soil retains moisture well for Mizuna, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Mizuna 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 Mizuna's growing requirements.
Soil pH
Your soil pH (5.6–6.6) overlaps with Mizuna's range (6.0–7.5), though not a perfect match.
Soil Texture
Your silty clay soil in Hawaii County is workable for Mizuna. Add compost annually to improve structure.
Organic Matter
Organic matter is excellent (4.1%) — Mizuna will thrive.
How to Plant Mizuna
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Plant Water Budget
Monthly Watering Guide for Mizuna
Mizuna needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Mizuna 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.
Mizuna 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.
Mizuna Planting Timeline — Hawaii County, HI
Mizuna Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | December 4 | Dec 4 – Dec 18 |
| Transplant Outdoors | January 1 | Jan 1 – Jan 15 |
| Direct Sow | December 11 | Dec 11 – Jan 1 |
| Harvest | February 5 | Feb 5 – Mar 5 |
| Fall Sowing | November 5 | Nov 5 – Nov 19 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | Harvest |
| March | Harvest |
| April | — |
| May | — |
| June | — |
| July | — |
| August | — |
| September | — |
| October | — |
| November | Fall Sowing |
| December | Start Indoors Direct Sow |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1"/week · Natural rainfall sufficient
📅 Days to Maturity
30–45 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 11a
📆 Growing Season
364 days in Hawaii County
Growing Tips for Mizuna in Hawaii County
With Hawaii County's clay soil (39% clay), work in 3-4 inches of compost before planting Mizuna. Avoid tilling when soil is wet to prevent compaction.
Your generous 365.0-day season in Hawaii County allows multiple plantings of Mizuna. Sow every 15.0 days for continuous harvest.
Common pests for Mizuna in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
General growing tips
Direct sow in spring or fall. Harvest outer leaves as needed for a cut-and-come-again approach. Mizuna is one of the most cold-tolerant Asian greens.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Mizuna in Other Locations
Frequently Asked Questions
When should I plant Mizuna in Hawaii County, HI?
Hawaii County is in Zone 11a with an average last frost of January 1. Plan your Mizuna 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 11a. 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 11a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.