When to plant Marigolds in Johnson County, IA
For Marigolds in Johnson County, the safe spring window opens around May 1 and closes around May 22. Last expected frost is April 24, first fall frost October 11, giving a 170-day growing season.
When to Plant Marigolds in Johnson County, IA
Your July game plan for Johnson County, Iowa
July rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Johnson County, Iowa.
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Start harvesting marigolds
Taste as you pick. The first ripe produce is the best feedback loop you'll get all season.
Coming up in August — start thinking about
- First harvests: marigolds
Marigolds (Tagetes patula) are warm-season annuals beloved for their cheerful orange, yellow, and red blooms — and for their well-documented ability to repel pest nematodes in vegetable beds. Easy from seed, drought-tolerant once established, and bloom from early summer until the first hard frost.
Johnson County, Iowa is in USDA Zone 5b. The average last spring frost is April 24 and the first fall frost is October 11, giving you a growing season of approximately 170 days.
At an elevation of 1,204 feet, Johnson County receives approximately 40.7 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Marigolds during the growing season.
Johnson County Soil Profile
Soil Type
Silt Loam
Soil pH
6.2-7.3
Drainage
Well Drained
Marigolds 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 Johnson County
How your county's soil matches Marigolds's growing requirements.
Soil pH
Your soil pH (6.2–7.3) is within Marigolds's preferred range (6.0–7.5).
Soil Texture
The silt loam soil in Johnson County is excellent for Marigolds — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.9%). Annual compost additions will help Marigolds.
How to Plant Marigolds
Succession Planting Marigolds
Sow every 5.7 weeks. Last sowing by Aug 02 to harvest before frost.
Marigolds Water Budget
Monthly Watering Guide for Marigolds
Marigolds 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 | Marigolds Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.8" | 0" | ❄️ Dormant |
| Feb | — | 2" | 0" | ❄️ Dormant |
| Mar | — | 2.8" | 0" | ❄️ Dormant |
| Apr | 2.2" | 3.7" | 0" | ✅ Rainfall sufficient |
| May | 2.2" | 4.8" | 0" | ✅ Rainfall sufficient |
| Jun | 2.2" | 5.4" | 0" | ✅ Rainfall sufficient |
| Jul | 2.2" | 4.5" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 3.6" | 0" | ✅ Rainfall sufficient |
| Sep | 2.2" | 3.6" | 0" | ✅ Rainfall sufficient |
| Oct | 2.2" | 3.4" | 0" | ✅ Rainfall sufficient |
| Nov | — | 2.9" | 0" | ❄️ Dormant |
| Dec | — | 2.3" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Johnson County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Marigolds 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.
Marigolds Planting Timeline — Johnson County, IA
Marigolds Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 13 | Mar 13 – Mar 27 |
| Transplant Outdoors | May 1 | May 1 – May 15 |
| Direct Sow | May 1 | May 1 – May 22 |
| Bloom | June 26 | Jun 26 – Sep 25 |
Plant 0.3" deep · 10" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors Direct Sow |
| June | Bloom |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Natural rainfall sufficient
📅 Days to Maturity
50–70 days
🧪 Soil pH
Needs 6–7.5 · Your soil: ideal
🗺️ USDA Zone
Zone 5b
📆 Growing Season
170 days in Johnson County
Growing Tips for Marigolds in Johnson County
Direct sow Marigolds outdoors after April 24 in Johnson County when soil has warmed and frost danger has passed.
Common pests for Marigolds 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 or start indoors 4-6 weeks earlier. Deadhead spent blooms to keep new flowers coming. French marigolds (T. patula) are the most reliable nematode repellents — plant a band around vegetable beds. Tolerate poor soil but bloom best with monthly compost.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Very easy to save. Seeds are the long, thin, dark pieces inside the dried flower head.
Marigolds in Other Locations
Frequently Asked Questions
When should I plant Marigolds in Johnson County, IA?
Johnson County is in Zone 5b with an average last frost of April 24. Plan your Marigolds planting based on this frost date — see the calendar above for exact timing.
What planting zone is Johnson County, IA?
Johnson County, Iowa is in USDA Hardiness Zone 5b. The average last spring frost is April 24 and first fall frost is October 11.
When should I plant Marigolds in Johnson County, IA?
In Johnson County, IA, plant Marigolds after the last frost (around April 24) and before the first frost (around October 11). Best results when soil holds above 50°F.
What growing zone is Johnson County, IA for Marigolds?
Johnson County sits in USDA Zone 5b. Marigolds grows reliably in zones 2a through 11b, so it's a good fit here.
Can Marigolds grow in Johnson County's climate?
Yes — Marigolds grows well in Johnson County's temperate climate. Johnson County averages a 170-day frost-free season, with last frost around April 24 and first frost around October 11.
Your Johnson County Garden Planner — Free
A 22-page printable planner built for Johnson County (Zone 5b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.