Fertilizing Celeriac: Compost, Organic Feeds, and Midseason Boosts

Celeriac is a slow-growing, nutrient-hungry crop, and over decades of gardening in Sonoma Valley, I’ve learned that soil fertility directly impacts root size and flavor. Too little nutrition produces small, fibrous bulbs, while too much nitrogen encourages leafy growth at the expense of the root. Striking the right balance with compost, organic fertilizers, and midseason boosts is essential for a bountiful harvest.

Table of Contents

Starting With Compost

Before planting, I enrich the soil with several inches of well-aged compost. This not only provides steady, slow-release nutrients but also improves soil structure, making it easier for the root to expand. In my experience, beds with a solid compost base produce larger, smoother, and more aromatic celeriac than those with synthetic fertilizers alone.

Organic Feeds at Planting

Along with compost, I often work in a balanced organic fertilizer—something like 5-5-5 or 4-6-4—to give young seedlings a gentle nutrient boost. I avoid high-nitrogen feeds, which push foliage growth and can reduce root development. This combination of compost and moderate organic feeding sets the foundation for steady, uniform growth throughout the season.

Midseason Fertilization

Celeriac grows slowly but steadily, so I provide a midseason nutrient boost about 4–6 weeks after transplanting. I side-dress with compost or sprinkle a light layer of organic granular fertilizer around the base, gently working it into the soil. In my experience, this encourages the swollen stem base to expand evenly without creating excessive leaf growth.

Additional Tips From Experience

Keep fertilizer away from the crown to avoid rot.
Water thoroughly after feeding to help nutrients penetrate the root zone.
Monitor plant growth—if leaves are pale or stunted, a small foliar feed of seaweed extract can help.

Bottom Line

Consistent, balanced fertility is crucial for producing large, flavorful celeriac. Compost, moderate organic feeds, and careful midseason boosts create ideal conditions for smooth, aromatic roots.