When to Plant Lettuce in Plymouth County, IA
April in the garden — Plymouth County, Iowa
We've pulled the most time-sensitive tasks for Plymouth County, Iowa this April and put them front and centre. Tackle them in order.
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Get lettuce in the ground
Frost risk is low now in Plymouth County, Iowa. If you've been covering beds overnight, you can stop.
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Plant lettuce from seed, right in the garden
Your soil is 41°F — warm enough for these to germinate without babying.
Lettuce is a fast-growing cool-season green available in leaf, romaine, butterhead, and crisphead types. It is the foundation of salads and one of the easiest crops to grow.
Plymouth County, Iowa is in USDA Zone 4b. The average last spring frost is April 30 and the first fall frost is October 6, giving you a growing season of approximately 159 days.
At an elevation of 1,392 feet, Plymouth County receives approximately 38 inches of rainfall annually with predominantly silt loam soil. Summer highs average 83°F, so choose short-season varieties of Lettuce to ensure they mature before fall.
Plymouth 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 Plymouth County
How your county's soil matches Lettuce's growing requirements.
Soil pH
Your soil pH (6.0–7.2) overlaps with Lettuce's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Plymouth County is excellent for Lettuce — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.7%) — Lettuce will thrive.
How to Plant Lettuce
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Lettuce
Sow every 3.4 weeks. Last sowing by Aug 07 to harvest before frost.
For a dedicated fall crop, sow by Jul 28.
Plant Water Budget
Monthly Watering Guide for Lettuce
Lettuce needs approximately 0.7 inches of water per week (3" per month). Here's how your county's rainfall compares month by month.
| Month | Lettuce Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.6" | 0" | ❄️ Dormant |
| Feb | — | 1.4" | 0" | ❄️ Dormant |
| Mar | — | 2.6" | 0" | ❄️ Dormant |
| Apr | 3" | 3.9" | 0" | ✅ Rainfall sufficient |
| May | 3" | 4.8" | 0" | ✅ Rainfall sufficient |
| Jun | 3" | 4.2" | 0" | ✅ Rainfall sufficient |
| Jul | 3" | 4.4" | 0" | ✅ Rainfall sufficient |
| Aug | 3" | 4.3" | 0" | ✅ Rainfall sufficient |
| Sep | 3" | 3.4" | 0" | ✅ Rainfall sufficient |
| Oct | 3" | 2.7" | 0.3" | 💧 Light watering |
| Nov | — | 2.8" | 0" | ❄️ Dormant |
| Dec | — | 1.9" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Plymouth County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Lettuce 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.
Lettuce Planting Timeline — Plymouth County, IA
Lettuce Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 19 | Mar 19 – Apr 2 |
| Transplant Outdoors | April 30 | Apr 30 – May 14 |
| Direct Sow | April 23 | Apr 23 – May 14 |
| Harvest | June 4 | Jun 4 – Aug 13 |
| Fall Sowing | July 14 | Jul 14 – Jul 28 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | Harvest |
| July | Fall Sowing Harvest |
| August | Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
0.7"/week · Natural rainfall sufficient
📅 Days to Maturity
30–60 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 4b
📆 Growing Season
159 days in Plymouth County
Growing Tips for Lettuce in Plymouth County
Direct sow Lettuce outdoors after April 30 in Plymouth County when soil has warmed and frost danger has passed.
Your generous 159.0-day season in Plymouth County allows multiple plantings of Lettuce. Sow every 15.0 days for continuous harvest.
Common pests for Lettuce in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Sow seeds directly every 2 weeks for continuous harvest. Provide afternoon shade in warm weather to delay bolting. Harvest in the morning for crispest leaves.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Very easy to save. Let a few plants bolt each season.
Lettuce in Other Locations
Frequently Asked Questions
When should I plant Lettuce in Plymouth County, IA?
Plymouth County is in Zone 4b with an average last frost of April 30. Plan your Lettuce planting based on this frost date — see the calendar above for exact timing.
What planting zone is Plymouth County, IA?
Plymouth County, Iowa is in USDA Hardiness Zone 4b. The average last spring frost is April 30 and first fall frost is October 6.
Your Plymouth County Garden Planner — Free
A 24-page printable planner built for Plymouth County (Zone 4b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.