When to Plant Radicchio in Whitman County, WA
Radicchio is an Italian chicory with stunning red and white leaves and a pleasantly bitter flavor. It forms tight heads and is used in salads, grilled, or braised.
Whitman County, Washington is in USDA Zone 6a. The average last spring frost is May 10 and the first fall frost is September 29, giving you a growing season of approximately 142 days.
At an elevation of 1,541 feet, Whitman County receives approximately 14.5 inches of rainfall annually with predominantly silt loam soil. Summer highs average 88°F, providing good warmth for Radicchio during the growing season. With low rainfall, drip irrigation is essential for growing Radicchio successfully. Mulch heavily to conserve soil moisture.
Whitman County Soil Profile
Soil Type
Silt Loam
Soil pH
5.5-6.7
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 Whitman County
How your county's soil matches Radicchio's growing requirements.
Soil pH
Your soil pH (5.5–6.7) overlaps with Radicchio's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Whitman County is excellent for Radicchio — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (5.0%) — Radicchio will thrive.
How to Plant Radicchio
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Radicchio
Sow every 6.9 weeks. Last sowing by Jul 11 to harvest before frost.
For a dedicated fall crop, sow by Jul 21.
Plant Water Budget
Monthly Watering Guide for Radicchio
Radicchio needs approximately 0.7 inches of water per week (3" per month). Here's how your county's rainfall compares month by month.
| Month | Radicchio Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 2.2" | 0" | ❄️ Dormant |
| Feb | — | 1.5" | 0" | ❄️ Dormant |
| Mar | — | 1.3" | 0" | ❄️ Dormant |
| Apr | — | 1.2" | 0" | ❄️ Dormant |
| May | 3" | 0.8" | 2.2" | 🚿 Regular watering |
| Jun | 3" | 0.6" | 2.4" | 🚿 Regular watering |
| Jul | 3" | 0.3" | 2.7" | 🚿 Regular watering |
| Aug | 3" | 0.2" | 2.8" | 🚿 Regular watering |
| Sep | 3" | 0.6" | 2.4" | 🚿 Regular watering |
| Oct | — | 1.3" | 0" | ❄️ Dormant |
| Nov | — | 2.2" | 0" | ❄️ Dormant |
| Dec | — | 2.5" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Whitman County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Radicchio 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.
Radicchio Planting Timeline — Whitman County, WA
Radicchio Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 5 | Apr 5 – Apr 19 |
| Transplant Outdoors | May 10 | May 10 – May 24 |
| Direct Sow | April 26 | Apr 26 – May 17 |
| Harvest | July 12 | Jul 12 – Aug 16 |
| Fall Sowing | July 21 | Jul 21 – Aug 4 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Fall Sowing Harvest |
| August | Fall Sowing Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.7"/week · Only during dry spells
📅 Days to Maturity
60–80 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 6a
📆 Growing Season
142 days in Whitman County
Growing Tips for Radicchio in Whitman County
Direct sow Radicchio outdoors after May 10 in Whitman County when soil has warmed and frost danger has passed.
Common pests for Radicchio in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
General growing tips
Start in late summer for fall harvest. The red color develops with cool nights and light frost. Harvest when heads are firm and compact.
Companion Planting
Good Companions
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Check more plant combinations with our Companion Planting Checker →
Radicchio in Other Locations
Frequently Asked Questions
When should I plant Radicchio in Whitman County, WA?
Whitman County is in Zone 6a with an average last frost of May 10. Plan your Radicchio planting based on this frost date — see the calendar above for exact timing.
What planting zone is Whitman County, WA?
Whitman County, Washington is in USDA Hardiness Zone 6a. The average last spring frost is May 10 and first fall frost is September 29.
Plan Your Garden with Confidence
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