When to plant Vinca (Annual) in Audubon County, IA
Audubon County's 158-day season only supports one Vinca (Annual) planting per year. Sow between May 12 and May 26 for the best chance at full maturity before October 3.
When to Plant Vinca (Annual) in Audubon County, IA
Audubon County, Iowa gardeners: here's your July plan
July is a pivotal month for Audubon County, Iowa gardens. Focus on these tasks first and you'll set up the rest of the season for success.
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Indoor seed-starting week for vinca (annual)
Bottom-water once the first true leaves appear — it keeps stems dry and knocks back damping-off.
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Collect vinca (annual) at their peak
Don't tug. Use scissors or pruners for clean cuts — torn stems invite disease.
August prep starts now
- 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.
Audubon County, Iowa is in USDA Zone 5a. The average last spring frost is April 28 and the first fall frost is October 3, giving you a growing season of approximately 158 days.
At an elevation of 1,056 feet, Audubon County receives approximately 32.5 inches of rainfall annually with predominantly silt loam soil. Summer highs average 86°F, providing good warmth for Vinca (Annual) during the growing season.
Audubon County Soil Profile
Soil Type
Silt Loam
Soil pH
5.8-6.8
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 Audubon County
How your county's soil matches Vinca (Annual)'s growing requirements.
Soil pH
Your soil pH (5.8–6.8) overlaps with Vinca (Annual)'s range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Audubon County is excellent for Vinca (Annual) — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.8%) — Vinca (Annual) will thrive.
How to Plant Vinca (Annual)
Succession Planting Vinca (Annual)
Sow every 8 weeks. Last sowing by Jul 05 to harvest before frost.
Vinca (Annual) Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
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 | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.3" | 0" | ❄️ Dormant |
| Mar | — | 2.1" | 0" | ❄️ Dormant |
| Apr | 2.2" | 3.2" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 4.4" | 0" | ✅ Rainfall sufficient |
| Jun | 2.2" | 3.7" | 0" | ✅ Rainfall sufficient |
| Jul | 2.2" | 3.9" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 3.5" | 0" | ✅ Rainfall sufficient |
| Sep | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| Oct | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| Nov | — | 2" | 0" | ❄️ Dormant |
| Dec | — | 1.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Audubon 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 — Audubon County, IA
Vinca (Annual) Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 10 | Feb 10 – Feb 24 |
| Transplant Outdoors | May 12 | May 12 – May 26 |
| Bloom | July 21 | Jul 21 – Oct 6 |
Plant 0.1" deep · 10" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | — |
| April | — |
| May | Transplant Outdoors |
| June | — |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| 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 5a
📆 Growing Season
158 days in Audubon County
Growing Tips for Vinca (Annual) in Audubon County
Direct sow Vinca (Annual) outdoors after April 28 in Audubon 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 Audubon County, IA?
Audubon County is in Zone 5a with an average last frost of April 28. Plan your Vinca (Annual) planting based on this frost date — see the calendar above for exact timing.
What planting zone is Audubon County, IA?
Audubon County, Iowa is in USDA Hardiness Zone 5a. The average last spring frost is April 28 and first fall frost is October 3.
When should I plant Vinca (Annual) in Audubon County, IA?
In Audubon County, IA, plant Vinca (Annual) after the last frost (around April 28) and before the first frost (around October 3). Best results when soil holds above 50°F.
What growing zone is Audubon County, IA for Vinca (Annual)?
Audubon County sits in USDA Zone 5a. Vinca (Annual) grows reliably in zones 3a through 11b, so it's a good fit here.
Can Vinca (Annual) grow in Audubon County's climate?
Yes — Vinca (Annual) grows well in Audubon County's temperate climate. Audubon County averages a 158-day frost-free season, with last frost around April 28 and first frost around October 3.
Your Audubon County Garden Planner — Free
A 22-page printable planner built for Audubon County (Zone 5a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.