Fertilizing Kohlrabi: Tips for Bigger, Sweeter Bulbs

Kohlrabi is a cool-season, heavy-feeding brassica that thrives with proper fertilization. With over 30 years of gardening experience, I’ve learned that feeding your plants correctly—from planting through growth—directly impacts bulb size, flavor, and overall plant health. In this guide, I’ll share step-by-step fertilizing strategies to help you achieve robust, tender, and sweet kohlrabi bulbs.

Table of Contents

Step 1: Preparing the Soil

Incorporate compost or aged manure before planting.
Work 2–3 inches of organic matter into the top 6–8 inches of soil.
Ensure soil is loose and well-draining to allow roots and bulbs to develop.

💡 Experience Tip: I’ve found that enriching the soil before planting reduces the need for heavy supplemental feeding later.

Step 2: Choosing Fertilizers

Nitrogen-rich fertilizers (like blood meal or fish emulsion) support leafy growth, which feeds the bulb.
Balanced fertilizers (N-P-K 10-10-10) can be used for steady growth.
Avoid over-fertilizing with nitrogen alone, which can create large leaves but small bulbs.

💡 Experience Tip: I often use a combination of compost and a light organic fertilizer to encourage both leaf and bulb development.

Step 3: Fertilizing During Growth

Side-dress when bulbs begin to form (about 3–4 weeks after planting).
Apply fertilizer evenly around the base, keeping it a few inches away from the crown.
Repeat side-dressing every 3–4 weeks for continuous growth.

💡 Experience Tip: Consistent, moderate feeding yields sweeter, tender bulbs compared to heavy, infrequent fertilization.

Step 4: Micronutrients and Soil Health

Kohlrabi benefits from calcium, magnesium, and boron for strong cell walls and smooth bulbs.
Incorporate lime or dolomitic lime if soil is acidic (pH <6.0).
Mulching and regular watering help nutrients reach roots efficiently.

Step 5: Fertilization for Container Kohlrabi

Use a high-quality potting mix with compost.
Supplement with liquid organic fertilizer every 2–3 weeks since nutrients leach faster in containers.
Ensure consistent moisture for optimal nutrient uptake.

My Experience

Proper fertilization is the key to growing bigger, sweeter kohlrabi bulbs. By preparing the soil, using a balanced feeding schedule, and monitoring micronutrients, gardeners can maximize yield and flavor. Consistent, hands-on care—backed by decades of experience—ensures your kohlrabi thrives from seedling to harvest.

Kohlrabi Fertilization Schedule

Stage	Fertilizer Type	Timing / Frequency	Application Tips	Experience Tip
Pre-Planting	Compost or aged manure	Work into soil 2–3 inches deep before planting	Mix into top 6–8 inches of soil	Pre-enriching soil reduces need for heavy feeding later
Early Growth	Nitrogen-rich (blood meal, fish emulsion)	2–3 weeks after seedlings emerge	Apply evenly around base, a few inches from crown	Supports leafy growth for bulb development
Bulb Formation	Balanced fertilizer (N-P-K 10-10-10)	When bulbs begin to form (3–4 weeks after planting)	Side-dress around base; water in	Moderate, consistent feeding yields tender, flavorful bulbs
Ongoing Growth	Organic liquid fertilizer	Every 3–4 weeks until harvest	Apply evenly to soil or as foliar feed	Keeps nutrients steady for continuous growth
Container Plants	High-quality potting mix + liquid fertilizer	Every 2–3 weeks	Nutrients leach faster in containers; maintain consistent moisture	Ensures bulbs develop fully in limited soil volume
Micronutrients	Lime, dolomitic lime, or trace mineral mix	As needed based on soil test	Incorporate into soil or sprinkle lightly around plants	Boosts calcium, magnesium, and boron for smooth, strong bulbs

💡 Gardener’s Tip from Experience:
Consistent, moderate feeding and regular monitoring of soil nutrients are key to growing bigger, sweeter kohlrabi bulbs in both gardens and containers.

Kohlrabi Growing Hub

Start here: The Ultimate Guide to Growing Kohlrabi: From Seed to Harvest

🌱 Planning & Varieties

Best Kohlrabi Varieties to Grow in Your Garden – Compare early, late, and specialty varieties for flavor, color, and growth speed.
When to Plant Kohlrabi: Seasonal Planting Guide – Spring, summer, and fall planting windows for cool, crisp bulbs.
Kohlrabi Companion Planting: Best and Worst Neighbors – Plants that boost growth or deter pests naturally.
Growing Kohlrabi in Containers and Small Spaces – Pot size, soil mix, and care for urban gardens.

🌿 Seed Starting & Transplanting

From seed to sturdy seedlings.

Kohlrabi Seed Starting Tips – Germination tips, soil temperature, and timing for successful strong plants.
How to Transplant Kohlrabi Seedlings Successfully – Hardening off, spacing, and planting depth for seedlings.
Kohlrabi Spacing and Layout for Maximum Yield – Row vs. raised bed spacing, companion planting considerations.

🌾 Care & Maintenance

Tips for strong growth and pest-free plants.