When to Plant Vinca (Annual) in Jefferson County, WA
Your June game plan for Jefferson County, Washington
Welcome to June in Zone 8b. These are the moves that will have the biggest impact on your growing season.
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Indoor seed-starting week for vinca (annual)
You're about 19 weeks out from your last frost — the perfect window to get these germinating indoors.
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Collect vinca (annual) at their peak
Check every 1–2 days. Many of these get tough or go to seed if you wait too long.
A few tasks this June that'll pay off in July
- First harvests: vinca (annual)
Annual vinca (Catharanthus roseus), also called Madagascar periwinkle, is one of the most heat- and drought-tolerant bedding plants available. Glossy foliage stays attractive all season while cheerful pinwheel blooms continue without deadheading. A top performer in hot, humid Southern summers where impatiens and begonias struggle. Self-cleaning; requires little maintenance once established.
Jefferson County, Washington is in USDA Zone 8b. The average last spring frost is April 14 and the first fall frost is October 29, giving you a growing season of approximately 198 days.
At an elevation of 205 feet, Jefferson County receives approximately 40.7 inches of rainfall annually with predominantly silt loam soil. Summer highs average 88°F, providing good warmth for Vinca (Annual) during the growing season.
Jefferson County Soil Profile
Soil Type
Silt Loam
Soil pH
5.7-6.8
Drainage
Well Drained
Vinca (Annual) 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 Jefferson County
How your county's soil matches Vinca (Annual)'s growing requirements.
Soil pH
Your soil pH (5.7–6.8) overlaps with Vinca (Annual)'s range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Jefferson County is excellent for Vinca (Annual) — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Vinca (Annual).
Organic Matter
Organic matter is excellent (5.7%) — Vinca (Annual) will thrive.
How to Plant Vinca (Annual)
Succession Planting Vinca (Annual)
Sow every 8 weeks. Last sowing by Jul 31 to harvest before frost.
Vinca (Annual) Water Budget
Monthly Watering Guide for Vinca (Annual)
Vinca (Annual) 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 | Vinca (Annual) Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 6.4" | 0" | ❄️ Dormant |
| Feb | — | 4.7" | 0" | ❄️ Dormant |
| Mar | — | 3.9" | 0" | ❄️ Dormant |
| Apr | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 2.1" | 0.1" | 💧 Light watering |
| Jun | 2.2" | 1.5" | 0.7" | 💧 Light watering |
| Jul | 2.2" | 0.5" | 1.7" | 🚿 Regular watering |
| Aug | 2.2" | 0.6" | 1.6" | 🚿 Regular watering |
| Sep | 2.2" | 1.6" | 0.6" | 💧 Light watering |
| Oct | 2.2" | 3.5" | 0" | ✅ Rainfall sufficient |
| Nov | — | 6.3" | 0" | ❄️ Dormant |
| Dec | — | 7.1" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Jefferson County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Vinca (Annual) 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.
Vinca (Annual) Planting Timeline — Jefferson County, WA
Vinca (Annual) Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 3 | Feb 3 – Feb 17 |
| Transplant Outdoors | March 31 | Mar 31 – Apr 14 |
| Bloom | June 9 | Jun 9 – Nov 10 |
Plant 0.1" deep · 10" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Transplant Outdoors |
| April | Transplant Outdoors |
| May | — |
| June | Bloom |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | Bloom |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Natural rainfall sufficient
📅 Days to Maturity
70–90 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 8b
📆 Growing Season
198 days in Jefferson County
Growing Tips for Vinca (Annual) in Jefferson County
Direct sow Vinca (Annual) outdoors after April 14 in Jefferson County when soil has warmed and frost danger has passed.
General growing tips
Start seeds indoors 10–12 weeks before last frost — germination requires warm soil (75–80°F) and darkness. Do not cover seeds deeply; they need just a light dusting. Direct sowing is rarely practiced due to slow seedling establishment. Transplant after soil warms and frost danger has passed. Excellent drought tolerance once established; avoid overwatering. Performs best in well-drained beds or containers in full sun.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Vinca (Annual) in Other Locations
Frequently Asked Questions
When should I plant Vinca (Annual) in Jefferson County, WA?
Jefferson County is in Zone 8b with an average last frost of April 14. Plan your Vinca (Annual) planting based on this frost date — see the calendar above for exact timing.
What planting zone is Jefferson County, WA?
Jefferson County, Washington is in USDA Hardiness Zone 8b. The average last spring frost is April 14 and first fall frost is October 29.
Your Jefferson County Garden Planner — Free
A 22-page printable planner built for Jefferson County (Zone 8b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.