When to Plant Watercress in Rock Island County, IL
May in the garden — Rock Island County, Illinois
Here's what deserves your attention in Rock Island County, Illinois this month. Everything below is tailored to Zone 5b and timed around your local frost dates.
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Start watercress under lights
You're about 24 weeks out from your last frost — the perfect window to get these germinating indoors.
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Bring in the watercress
Morning harvests are best — cooler temperatures mean crisper produce and longer fridge life.
Get ahead of June
- First harvests: watercress
Watercress is a semi-aquatic plant with a peppery, tangy flavor rich in vitamins and minerals. It grows naturally along streams and can be cultivated in containers with standing water.
Rock Island County, Illinois is in USDA Zone 5b. The average last spring frost is April 15 and the first fall frost is October 19, giving you a growing season of approximately 187 days.
At an elevation of 1,172 feet, Rock Island County receives approximately 35.8 inches of rainfall annually with predominantly silt loam soil. Summer highs average 83°F, so choose short-season varieties of Watercress to ensure they mature before fall.
Rock Island County Soil Profile
Soil Type
Silt Loam
Soil pH
6.3-6.9
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 Rock Island County
How your county's soil matches Watercress's growing requirements.
Soil pH
Your soil pH (6.3–6.9) overlaps with Watercress's range (6.5–7.5), though not a perfect match.
Soil Texture
The silt loam soil in Rock Island County is excellent for Watercress — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.7%) — Watercress will thrive.
How to Plant Watercress
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Watercress
Sow every 4.6 weeks. Last sowing by Aug 20 to harvest before frost.
For a dedicated fall crop, sow by Aug 10.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Watercress
Watercress needs approximately 1.5 inches of water per week (6.5" per month). Here's how your county's rainfall compares month by month.
| Month | Watercress Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.7" | 0" | ❄️ Dormant |
| Feb | — | 1.4" | 0" | ❄️ Dormant |
| Mar | — | 2.2" | 0" | ❄️ Dormant |
| Apr | 6.5" | 3.6" | 2.9" | 💧 Light watering |
| May | 6.5" | 4.2" | 2.3" | 💧 Light watering |
| Jun | 6.5" | 4.7" | 1.8" | 💧 Light watering |
| Jul | 6.5" | 3.5" | 3" | 💧 Light watering |
| Aug | 6.5" | 4.2" | 2.3" | 💧 Light watering |
| Sep | 6.5" | 2.7" | 3.8" | 🚿 Regular watering |
| Oct | 6.5" | 2.8" | 3.7" | 🚿 Regular watering |
| Nov | — | 2.6" | 0" | ❄️ Dormant |
| Dec | — | 2.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Rock Island County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Watercress 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.
Watercress Planting Timeline — Rock Island County, IL
Watercress Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 11 | Mar 11 – Mar 25 |
| Transplant Outdoors | April 15 | Apr 15 – Apr 29 |
| Direct Sow | April 1 | Apr 1 – Apr 22 |
| Harvest | May 27 | May 27 – Jul 1 |
| Fall Sowing | August 10 | Aug 10 – Aug 24 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | Fall Sowing |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1.5"/week · 2-3 times/week
📅 Days to Maturity
40–60 days
🧪 Soil pH
Needs 6.5–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 5b
📆 Growing Season
187 days in Rock Island County
Growing Tips for Watercress in Rock Island County
Direct sow Watercress outdoors after April 15 in Rock Island County when soil has warmed and frost danger has passed.
Your generous 187.0-day season in Rock Island County allows multiple plantings of Watercress. Sow every 20.0 days for continuous harvest.
Common pests for Watercress in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
General growing tips
Grow in containers with trays of water kept fresh. Provide partial shade and cool conditions. Harvest stems by cutting above water level. Replace water frequently to prevent stagnation.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Watercress in Other Locations
Frequently Asked Questions
When should I plant Watercress in Rock Island County, IL?
Rock Island County is in Zone 5b with an average last frost of April 15. Plan your Watercress planting based on this frost date — see the calendar above for exact timing.
What planting zone is Rock Island County, IL?
Rock Island County, Illinois is in USDA Hardiness Zone 5b. The average last spring frost is April 15 and first fall frost is October 19.
Your Rock Island County Garden Planner — Free
A 24-page printable planner built for Rock Island 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.