Intermediate Kohlrabi Growing: Varieties, Succession & Season Extension

Intermediate Kohlrabi Growing: Varieties, Succession & Season Extension

Ready to take your kohlrabi growing beyond the basics? This intermediate guide explores the full spectrum of kohlrabi varieties, teaches succession planting for continuous harvest, and reveals techniques for managing pests and extending your growing season. Whether you're growing for your family or the farmers market, these techniques will enhance your kohlrabi production.

Deep Dive into Kohlrabi Varieties

Understanding Kohlrabi Classification

All kohlrabi belongs to the same species as cabbage, broccoli, and kale (Brassica oleracea), but has been selected for its swollen stem. Varieties differ primarily in:

• Skin color (green/white vs. purple)
• Size potential
• Days to maturity
• Tendency to become woody
• Cold tolerance

Comprehensive Variety Guide

Standard Early Varieties (50-60 days):

Mid-Season Varieties (60-75 days):

Giant Varieties (80-100+ days):

Variety Selection by Purpose

For Fresh Eating (Raw):

• Best: Kolibri, Quickstar, Winner
• Characteristics: Very tender, sweet, minimal fiber

For Cooking:

• Best: Grand Duke, Kossak, Gigante
• Characteristics: Holds texture, good flavor development

For Storage:

• Best: Kossak, Gigante, White Danube
• Characteristics: Dense flesh, stores well

For Market Sales:

• Best: Kolibri (purple appeal), Grand Duke (uniformity)
• Characteristics: Eye-catching appearance, consistent size

Succession Planting Mastery

Planning Your Harvest Calendar

Basic Succession Principle: Plant new seeds or transplants every 2-3 weeks for continuous harvest.

Spring Succession Schedule (Zones 5-7):

Fall Focus Strategy: Many gardeners find fall kohlrabi superior to spring:

• Cooler temperatures = sweeter flavor
• Fewer pest problems
• Better storage quality
• Light frost improves sweetness

Calculating Planting Quantities

For Family of 4:

• Weekly consumption: 4-6 bulbs
• Days to maturity: ~55 (average)
• Plant loss estimate: 10-15%
• Recommendation: Plant 8-10 plants every 2-3 weeks

For Farmers Market:

• Track sales to determine demand
• Plant 25-50% more than expected
• Consider both standard and purple varieties for visual appeal

Soil and Nutrient Optimization

Ideal Soil Conditions

Soil Test Targets:

Fertilization Program

Pre-Plant:

• Incorporate 2-4 inches of compost
• Apply balanced fertilizer (4-4-4 or 10-10-10) at 2-3 lbs/100 sq ft
• Ensure adequate boron levels

Growing Season:

Special Considerations

Avoiding Hollow Stem:

• Maintain consistent moisture
• Ensure adequate boron (foliar spray 0.5 tsp borax/gallon if deficient)
• Don't over-fertilize with nitrogen

Preventing Woodiness:

• Harvest at proper size
• Maintain cool temperatures if possible
• Choose slow-to-woody varieties (Gigante, Kossak, Winner)

Integrated Pest Management

Common Pest Identification

Cabbage Worms (Imported Cabbage White):

Control:

• Row covers (most effective prevention)
• Bt (Bacillus thuringiensis) sprays
• Hand-picking
• Encourage parasitic wasps

Cabbage Aphids:

Control:

• Strong water spray to dislodge
• Insecticidal soap
• Ladybugs and lacewings (biological control)
• Avoid excess nitrogen

Flea Beetles:

Control:

• Row covers
• Trap crops (radish or Chinese cabbage)
• Kaolin clay spray
• Yellow sticky traps

Disease Prevention

Clubroot (Plasmodiophora brassicae): The most serious soil-borne disease of brassicas.

Black Rot (Xanthomonas campestris):

Biological Controls

Beneficial Insects:

Season Extension Techniques

Row Covers

Timing and Application:

Installation:

1. Install immediately after planting
2. Secure edges with soil, sandbags, or pins
3. Allow slack for plant growth
4. Remove for harvesting, then replace

Cold Frames for Fall/Winter

Design Specifications:

• South-facing orientation
• 18-24" back height, 12" front height
• Clear polycarbonate or glass lid
• Ventilation when temperatures exceed 45°F

Management:

• Plant fall kohlrabi in August-September
• Move to cold frame as weather cools
• Ventilate on warm days
• Harvest as needed through winter

Low Tunnels

Construction:

1. Install wire hoops (9-gauge, 5-6' wide arc)
2. Space hoops every 4-5 feet
3. Cover with greenhouse plastic or row cover
4. Secure edges

Benefits:

• Extends fall harvest 4-6 weeks
• Enables earlier spring planting
• Protects from frost to 15°F with double layer

Harvest Optimization

Harvest Timing by Variety Type

Signs of Over-Maturity

• Cracking at stem base
• Fibrous texture when cut
• Hollow areas in flesh
• Leaves yellowing and falling

Post-Harvest Handling

Immediate Steps:

1. Harvest in cool part of day
2. Cut leaves off immediately (they draw moisture from bulb)
3. Leave 1" of stem attached
4. Brush off soil (don't wash for storage)

Storage Conditions:

• Temperature: 32-40°F (0-4°C)
• Humidity: 90-95%
• Duration: 2-3 months (optimal conditions)

Troubleshooting Intermediate Issues

Problem: Variable bulb sizes at harvest

• Cause: Uneven germination, inconsistent spacing
• Solution: Transplant uniform seedlings, precise spacing

Problem: Purple color fading on purple varieties

• Cause: High temperatures, too much sun
• Solution: Normal in heat; harvest earlier or provide light shade

Problem: Cracked bulbs

• Cause: Irregular watering, especially heavy rain after drought
• Solution: Consistent irrigation, mulching

Problem: Off-flavors (bitter, pungent)

• Cause: Heat stress, water stress, over-maturity
• Solution: Grow in cool weather, maintain moisture, harvest promptly

Next Steps: Advancing Your Skills

Ready for more advanced techniques? Consider:

1. Saving seeds from open-pollinated varieties
2. Trialing new varieties for your microclimate
3. Implementing commercial-scale production
4. Exploring hydroponic kohlrabi

With these intermediate techniques, you'll achieve consistent, high-quality kohlrabi harvests throughout the growing season.