When to Plant Basil in Grundy County, IA
Your May gardening checklist
If you only do a handful of things in the garden this May, make it these. They're sequenced around your zone's frost timing.
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Transplant basil outside
Plant tomatoes deep — bury the stem up to the first true leaves to grow extra roots. Everything else goes in at the same depth it grew in the tray.
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Scatter basil into prepared beds
Your soil is 58°F — warm enough for these to germinate without babying.
June prep starts now
- Starting indoors: basil
Basil is a fragrant warm-season herb essential to Italian and Thai cuisines. It comes in many varieties including sweet, Thai, purple, and lemon types.
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 Basil to ensure they mature before fall.
Grundy County Soil Profile
Soil Type
Silt Loam
Soil pH
6-7.2
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 Grundy County
How your county's soil matches Basil's growing requirements.
Soil pH
Your soil pH (6.0–7.2) overlaps with Basil's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Grundy County is excellent for Basil — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.9%). Annual compost additions will help Basil.
How to Plant Basil
Succession Planting Basil
Sow every 5.7 weeks. Last sowing by Jul 26 to harvest before frost.
Plant Water Budget
Monthly Watering Guide for Basil
Basil needs approximately 0.6 inches of water per week (2.6" per month). Here's how your county's rainfall compares month by month.
| Month | Basil Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 2.1" | 0" | ❄️ Dormant |
| Apr | 2.6" | 3.2" | 0" | ✅ Rainfall sufficient |
| May | 2.6" | 3.3" | 0" | ✅ Rainfall sufficient |
| Jun | 2.6" | 4.1" | 0" | ✅ Rainfall sufficient |
| Jul | 2.6" | 3.1" | 0" | ✅ Rainfall sufficient |
| Aug | 2.6" | 3.6" | 0" | ✅ Rainfall sufficient |
| Sep | 2.6" | 2.5" | 0.1" | 💧 Light watering |
| Oct | 2.6" | 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.
Basil 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.
Basil Planting Timeline — Grundy County, IA
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 10 | Mar 10 – Mar 24 |
| Transplant Outdoors | May 12 | May 12 – May 26 |
| Direct Sow | May 5 | May 5 – May 26 |
| Harvest | July 7 | Jul 7 – Sep 8 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.6"/week · Natural rainfall sufficient
📅 Days to Maturity
50–75 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 5a
📆 Growing Season
164 days in Grundy County
Growing Tips for Basil in Grundy County
Direct sow Basil outdoors after April 28 in Grundy County when soil has warmed and frost danger has passed.
General growing tips
Start seeds indoors or direct sow after last frost. Pinch flower buds to extend leaf production. Harvest leaves from the top down, cutting just above a leaf pair.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Isolate 150 ft between varieties. Different basil species can cross.
Basil in Other Locations
Frequently Asked Questions
When should I plant Basil in Grundy County, IA?
Grundy County is in Zone 5a with an average last frost of April 28. Plan your Basil 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.
Your Grundy County Garden Planner — Free
A 24-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.