When to plant Zinnia in Grundy County County,
In Zone 5a (Grundy County County), direct-sow Zinnia between May 5 and May 26 for spring, after the April 28 last-frost mark.
When to Plant Zinnia in Grundy County, IA
This month in Grundy County, Iowa
June is a pivotal month for Grundy County, Iowa gardens. Focus on these tasks first and you'll set up the rest of the season for success.
Coming up in July — start thinking about
- First harvests: zinnia
Zinnia (Zinnia elegans) is a fast-growing, heat-loving annual that produces bold, dahlia-like blooms from early summer until hard frost. One of the easiest flowers to grow from direct-sown seed, zinnias thrive in hot, dry conditions and are magnets for butterflies and beneficial insects. They make excellent companion plants alongside marigolds in the vegetable garden.
Grundy County, Iowa is in USDA Zone 5a. The average last spring frost is April 28 and the first fall frost is October 9, giving you a growing season of approximately 164 days.
At an elevation of 984 feet, Grundy County receives approximately 30.2 inches of rainfall annually with predominantly silt loam soil. Summer highs average 83°F, so choose short-season varieties of Zinnia to ensure they mature before fall.
Grundy County Soil Profile
Soil Type
Silt Loam
Soil pH
6-7.2
Drainage
Well Drained
Zinnia 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 Grundy County
How your county's soil matches Zinnia's growing requirements.
Soil pH
Your soil pH (6.0–7.2) is within Zinnia's preferred range (5.5–7.5).
Soil Texture
The silt loam soil in Grundy County is excellent for Zinnia — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.9%). Annual compost additions will help Zinnia.
How to Plant Zinnia
Succession Planting Zinnia
Sow every 6.9 weeks. Last sowing by Jul 31 to harvest before frost.
Zinnia Water Budget
Monthly Watering Guide for Zinnia
Zinnia 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 | Zinnia Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 2.1" | 0" | ❄️ Dormant |
| Apr | 2.2" | 3.2" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 3.3" | 0" | ✅ Rainfall sufficient |
| Jun | 2.2" | 4.1" | 0" | ✅ Rainfall sufficient |
| Jul | 2.2" | 3.1" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 3.6" | 0" | ✅ Rainfall sufficient |
| Sep | 2.2" | 2.5" | 0" | ✅ Rainfall sufficient |
| Oct | 2.2" | 2.6" | 0" | ✅ Rainfall sufficient |
| Nov | — | 1.9" | 0" | ❄️ Dormant |
| Dec | — | 1.5" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Grundy County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Zinnia 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.
Zinnia Planting Timeline — Grundy County, IA
Zinnia Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 31 | Mar 31 – Apr 14 |
| Transplant Outdoors | May 5 | May 5 – May 19 |
| Direct Sow | May 5 | May 5 – May 26 |
| Bloom | July 14 | Jul 14 – Oct 6 |
Plant 0.3" deep · 12" apart · Rows 18" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| 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
60–70 days
🧪 Soil pH
Needs 5.5–7.5 · Your soil: ideal
🗺️ USDA Zone
Zone 5a
📆 Growing Season
164 days in Grundy County
Growing Tips for Zinnia in Grundy County
Direct sow Zinnia outdoors after April 28 in Grundy County when soil has warmed and frost danger has passed.
Common pests for Zinnia in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Direct-sow after last frost when soil reaches 60°F; seeds germinate in 5-7 days. In zones 3-5 a brief indoor start (4 weeks) is worthwhile but transplant carefully — zinnias dislike root disturbance. Deadhead frequently to extend bloom. Excellent cut flower; harvesting regularly encourages branching. Avoid overhead watering to reduce powdery mildew.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Zinnia in Other Locations
Frequently Asked Questions
When should I plant Zinnia in Grundy County, IA?
Grundy County is in Zone 5a with an average last frost of April 28. Plan your Zinnia planting based on this frost date — see the calendar above for exact timing.
What planting zone is Grundy County, IA?
Grundy County, Iowa is in USDA Hardiness Zone 5a. The average last spring frost is April 28 and first fall frost is October 9.
When should I plant Zinnia in Grundy County County, ?
In Grundy County County, , plant Zinnia after the last frost (around April 28) and before the first frost (around October 9). Best results when soil holds above 50°F.
What growing zone is Grundy County County, for Zinnia?
Grundy County County sits in USDA Zone 5a. Zinnia grows reliably in zones 3a through 11b, so it's a good fit here.
Can Zinnia grow in Grundy County County's climate?
Yes — Zinnia grows well in Grundy County County's temperate climate. Grundy County County averages a 164-day frost-free season, with last frost around April 28 and first frost around October 9.
Your Grundy County Garden Planner — Free
A 22-page printable planner built for Grundy 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.