When to Plant Sweet Potatoes in Alexander County, IL
Sweet potatoes are a warm-season root crop that produces nutritious, sweet tubers in orange, white, and purple varieties. They need a long, hot growing season.
Alexander County, Illinois is in USDA Zone 7a. The average last spring frost is April 10 and the first fall frost is October 21, giving you a growing season of approximately 194 days.
At an elevation of 1,260 feet, Alexander County receives approximately 38.6 inches of rainfall annually with predominantly silt loam soil. Summer highs average 88°F, providing good warmth for Sweet Potatoes during the growing season.
Alexander County Soil Profile
Soil Type
Silt Loam
Soil pH
5.9-7
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 Alexander County
How your county's soil matches Sweet Potatoes's growing requirements.
Soil pH
Your soil pH (5.9–7.0) overlaps with Sweet Potatoes's range (5.5–6.5), though not a perfect match.
Soil Texture
The silt loam soil in Alexander County is excellent for Sweet Potatoes — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (4.0%). Annual compost additions will help Sweet Potatoes.
How to Plant Sweet Potatoes
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Sweet Potatoes
Sweet Potatoes needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Sweet Potatoes Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.6" | 0" | ❄️ Dormant |
| Feb | — | 1.6" | 0" | ❄️ Dormant |
| Mar | — | 3" | 0" | ❄️ Dormant |
| Apr | 4.3" | 4.3" | 0" | ✅ Rainfall sufficient |
| May | 4.3" | 4.1" | 0.2" | 💧 Light watering |
| Jun | 4.3" | 5.1" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 3.8" | 0.5" | 💧 Light watering |
| Aug | 4.3" | 4.8" | 0" | ✅ Rainfall sufficient |
| Sep | 4.3" | 3" | 1.3" | 💧 Light watering |
| Oct | 4.3" | 3" | 1.3" | 💧 Light watering |
| Nov | — | 2.4" | 0" | ❄️ Dormant |
| Dec | — | 2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Alexander County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Sweet Potatoes 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.
Sweet Potatoes Planting Timeline — Alexander County, IL
Sweet Potatoes Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 20 | Feb 20 – Mar 6 |
| Transplant Outdoors | April 24 | Apr 24 – May 8 |
| Direct Sow | April 17 | Apr 17 – May 8 |
| Harvest | July 24 | Jul 24 – Sep 11 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Only during dry spells
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 5.5–6.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 7a
📆 Growing Season
194 days in Alexander County
Growing Tips for Sweet Potatoes in Alexander County
Direct sow Sweet Potatoes outdoors after April 10 in Alexander County when soil has warmed and frost danger has passed.
General growing tips
Plant slips (rooted sprouts) after soil is thoroughly warm. Build raised mounds for better root development. Cure harvested roots at 80-85F for 10 days to develop sweetness.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Sweet Potatoes in Other Locations
Frequently Asked Questions
When should I plant Sweet Potatoes in Alexander County, IL?
Alexander County is in Zone 7a with an average last frost of April 10. Plan your Sweet Potatoes planting based on this frost date — see the calendar above for exact timing.
What planting zone is Alexander County, IL?
Alexander County, Illinois is in USDA Hardiness Zone 7a. The average last spring frost is April 10 and first fall frost is October 21.
Plan Your Garden with Confidence
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