When to Plant Kohlrabi in Jefferson County, ID
Jefferson County, Idaho gardeners: here's your May plan
May rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Jefferson County, Idaho.
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Transplant kohlrabi outside
Frost risk is low now in Jefferson County, Idaho. If you've been covering beds overnight, you can stop.
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Outdoor sowing time: kohlrabi
Your soil is 43°F — warm enough for these to germinate without babying.
To set up a strong June, finish these tasks
- Starting indoors: kohlrabi
Kohlrabi is an unusual brassica that forms a swollen stem above ground with a mild, sweet turnip-like flavor. Both the bulb and tender leaves are edible.
Jefferson County, Idaho is in USDA Zone 5a. The average last spring frost is May 22 and the first fall frost is September 21, giving you a growing season of approximately 122 days.
At an elevation of 5,094 feet, Jefferson County receives approximately 18 inches of rainfall annually with predominantly loam soil. Summer highs average 87°F, providing good warmth for Kohlrabi during the growing season. With low rainfall, drip irrigation is essential for growing Kohlrabi successfully. Mulch heavily to conserve soil moisture.
Jefferson County Soil Profile
Soil Type
Loam
Soil pH
6.3-7.8
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 Jefferson County
How your county's soil matches Kohlrabi's growing requirements.
Soil pH
Your soil pH (6.3–7.8) overlaps with Kohlrabi's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Jefferson County is excellent for Kohlrabi — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.4%). Annual compost additions will help Kohlrabi.
How to Plant Kohlrabi
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Kohlrabi
Sow every 5.1 weeks. Last sowing by Jul 18 to harvest before frost.
For a dedicated fall crop, sow by Jul 13.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Kohlrabi
Kohlrabi needs approximately 0.7 inches of water per week (3" per month). Here's how your county's rainfall compares month by month.
| Month | Kohlrabi Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.1" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 1.4" | 0" | ❄️ Dormant |
| Apr | — | 2" | 0" | ❄️ Dormant |
| May | 3" | 1.9" | 1.1" | 💧 Light watering |
| Jun | 3" | 1.4" | 1.6" | 🚿 Regular watering |
| Jul | 3" | 1.4" | 1.6" | 🚿 Regular watering |
| Aug | 3" | 2" | 1" | 💧 Light watering |
| Sep | 3" | 1.6" | 1.4" | 💧 Light watering |
| Oct | — | 1.6" | 0" | ❄️ Dormant |
| Nov | — | 1.3" | 0" | ❄️ Dormant |
| Dec | — | 1" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Jefferson County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Kohlrabi 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.
Kohlrabi Planting Timeline — Jefferson County, ID
Kohlrabi Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 17 | Apr 17 – May 1 |
| Transplant Outdoors | May 22 | May 22 – Jun 5 |
| Direct Sow | May 8 | May 8 – May 29 |
| Harvest | July 10 | Jul 10 – Aug 14 |
| Fall Sowing | July 13 | Jul 13 – Jul 27 |
Plant 0.5" deep · 4" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Start Indoors Transplant Outdoors Direct Sow |
| June | Transplant Outdoors |
| July | Fall Sowing Harvest |
| August | Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.7"/week · Only during dry spells
📅 Days to Maturity
45–65 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 5a
📆 Growing Season
122 days in Jefferson County
Growing Tips for Kohlrabi in Jefferson County
Direct sow Kohlrabi outdoors after May 22 in Jefferson County when soil has warmed and frost danger has passed.
Common pests for Kohlrabi in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
General growing tips
Direct sow in spring or fall. Harvest when bulbs are 2-3 inches in diameter for best texture and flavor. Larger bulbs may become woody and fibrous.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Kohlrabi in Other Locations
Frequently Asked Questions
When should I plant Kohlrabi in Jefferson County, ID?
Jefferson County is in Zone 5a with an average last frost of May 22. Plan your Kohlrabi planting based on this frost date — see the calendar above for exact timing.
What planting zone is Jefferson County, ID?
Jefferson County, Idaho is in USDA Hardiness Zone 5a. The average last spring frost is May 22 and first fall frost is September 21.
Your Jefferson County Garden Planner — Free
A 24-page printable planner built for Jefferson 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.