Fertilizer for Leeks: NPK Guide and Application Rates
Leeks are a refined member of the onion family prized for their mild, sweet flavor and thick, blanched white shaft. Growing thick leeks requires consistent nitrogen feeding and progressive hilling of soil around the shaft to blanch and extend the white portion.
Quick Reference
What NPK Ratio is Best for Leeks?
The recommended NPK ratio for leeks is 10-10-10. A balanced 10-10-10 feeds all three macronutrients equally, which works well when soil tests show no single deficiency.
Leeks NPK needs shift at each growth stage. Balanced starter for transplants set in trenches during the Seedling phase, then not applicable; harvest before flowering once flowering begins.
NPK by Growth Stage for Leeks
| Growth Stage | NPK Ratio | Notes |
|---|---|---|
| Seedling | 10N 10P 10K N 10% Nitrogen: leaf and stem growth P 10% Phosphorus: roots and flowers K 10% Potassium: health and disease resistance Learn more about NPK | Balanced starter for transplants set in trenches |
| Vegetative | 15N 5P 10K N 15% Nitrogen: leaf and stem growth P 5% Phosphorus: roots and flowers K 10% Potassium: health and disease resistance Learn more about NPK | Nitrogen-forward for thick white shaft growth |
| Flowering | 10N 10P 10K N 10% Nitrogen: leaf and stem growth P 10% Phosphorus: roots and flowers K 10% Potassium: health and disease resistance Learn more about NPK | Not applicable; harvest before flowering |
| Fruiting | 5N 10P 10K N 5% Nitrogen: leaf and stem growth P 10% Phosphorus: roots and flowers K 10% Potassium: health and disease resistance Learn more about NPK | Reduce nitrogen as harvest approaches |
When Should You Fertilize Leeks?
In zone 3, start fertilizing leeks in May. In zone 10, begin as early as January. Apply every 3 weeks through the growing season.
Which Zones Can Grow Leeks?
Leeks grows in USDA zones 3 through 10, spanning a 8-zone range.
Fertilization Start by Zone
| Zone | Start Month |
|---|---|
| Zone 3 | May |
| Zone 4 | May |
| Zone 5 | April |
| Zone 6 | March |
| Zone 7 | March |
| Zone 8 | February |
| Zone 9 | February |
| Zone 10 | January |
What Are the Best Fertilizer Products for Leeks?
Look for products with an NPK close to 10-10-10. Espoma Garden-tone is the most popular choice among home gardeners for leeks.
- Espoma Garden-tone
- Neptune's Harvest Fish Fertilizer
- Down to Earth Blood Meal
Prices vary by retailer and region. Check current pricing before purchasing.
Container and Raised Bed Adjustments for Leeks
Container leeks need deep pots (12+ inches) and biweekly liquid nitrogen feeding; hill with soil as they grow
Common Fertilizing Mistakes with Leeks
- Not hilling soil around the shaft results in short, green, strong-flavored leeks
- Insufficient nitrogen produces pencil-thin shafts instead of thick, tender leeks
- Transplanting seedlings too deeply without hardening off causes rot at the base
Tips for Fertilizing Leeks
- Plant leeks in a 6-inch trench and gradually fill with soil as they grow to blanch the shaft
- Side-dress with nitrogen every 3 weeks for maximum shaft thickness
- Leeks are very cold-hardy and can be harvested well into winter in many zones
Organic Fertilizer Alternatives for Leeks
Sources
Source:Utah State University Extension - Growing LeeksLast updated: