When to Plant Rosemary in Onslow County, NC
Rosemary is an aromatic evergreen shrub with needle-like leaves and a piney, citrus flavor. It is a Mediterranean herb that thrives in warm, dry conditions.
Onslow County, North Carolina is in USDA Zone 8a. The average last spring frost is March 21 and the first fall frost is November 18, giving you a growing season of approximately 242 days.
At an elevation of 541 feet, Onslow County receives approximately 46.8 inches of rainfall annually with predominantly clay loam soil. Summer highs average 90°F, providing good warmth for Rosemary during the growing season. Clay soil retains moisture well for Rosemary, but amend with compost to improve drainage and prevent root rot.
Onslow County Soil Profile
Soil Type
Clay Loam
Soil pH
5.5-6.2
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 Onslow County
How your county's soil matches Rosemary's growing requirements.
Soil pH
Your soil pH (5.5–6.2) is more acidic than Rosemary prefers (6.0–7.5). Add garden lime to raise pH.
Soil Texture
The clay loam soil in Onslow County is excellent for Rosemary — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.3%). Annual compost additions will help Rosemary.
How to Plant Rosemary
Succession Planting Rosemary
Sow every 9.1 weeks. Last sowing by May 22 to harvest before frost.
Plant Water Budget
Monthly Watering Guide for Rosemary
Rosemary needs approximately 0.3 inches of water per week (1.3" per month). Here's how your county's rainfall compares month by month.
| Month | Rosemary Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 4" | 0" | ❄️ Dormant |
| Feb | — | 3.9" | 0" | ❄️ Dormant |
| Mar | 1.3" | 4.2" | 0" | ✅ Rainfall sufficient |
| Apr | 1.3" | 3.1" | 0" | ✅ Rainfall sufficient |
| May | 1.3" | 4" | 0" | ✅ Rainfall sufficient |
| Jun | 1.3" | 4.2" | 0" | ✅ Rainfall sufficient |
| Jul | 1.3" | 4.3" | 0" | ✅ Rainfall sufficient |
| Aug | 1.3" | 4.1" | 0" | ✅ Rainfall sufficient |
| Sep | 1.3" | 3.8" | 0" | ✅ Rainfall sufficient |
| Oct | 1.3" | 3.1" | 0" | ✅ Rainfall sufficient |
| Nov | 1.3" | 4" | 0" | ✅ Rainfall sufficient |
| Dec | — | 4" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Mar–Nov in Onslow County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Rosemary 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.
Rosemary Planting Timeline — Onslow County, NC
Rosemary Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Transplant Outdoors | March 28 | Mar 28 – Apr 11 |
| Harvest | June 20 | Jun 20 – Nov 7 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Transplant Outdoors |
| April | Transplant Outdoors |
| May | — |
| June | Harvest |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | Harvest |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.3"/week · Natural rainfall sufficient
📅 Days to Maturity
80–180 days
🧪 Soil pH
Needs 6–7.5 · Your soil: too_acidic
🗺️ USDA Zone
Zone 8a
📆 Growing Season
242 days in Onslow County
Growing Tips for Rosemary in Onslow County
Direct sow Rosemary outdoors after March 21 in Onslow County when soil has warmed and frost danger has passed.
With Onslow County's clay soil (30% clay), work in 3-4 inches of compost before planting Rosemary. Avoid tilling when soil is wet to prevent compaction.
General growing tips
Grow in well-drained soil and avoid overwatering. In cold climates, grow in containers and bring indoors for winter. Propagate from stem cuttings for faster results than seed.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Rosemary in Other Locations
Frequently Asked Questions
When should I plant Rosemary in Onslow County, NC?
Onslow County is in Zone 8a with an average last frost of March 21. Plan your Rosemary planting based on this frost date — see the calendar above for exact timing.
What planting zone is Onslow County, NC?
Onslow County, North Carolina is in USDA Hardiness Zone 8a. The average last spring frost is March 21 and first fall frost is November 18.
Plan Your Garden with Confidence
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