Fertilizer for Rhubarb: NPK Guide and Application Rates
Rhubarb is a cold-hardy perennial that thrives in northern climates and can produce for 10-15 years. It is a moderate feeder that responds well to annual spring fertilization and a generous fall mulch of aged compost. Thick, productive stalks depend on a well-fed, established crown.
Quick Reference
What NPK Ratio is Best for Rhubarb?
The recommended NPK ratio for rhubarb is 10-10-10. A balanced 10-10-10 feeds all three macronutrients equally, which works well when soil tests show no single deficiency.
Rhubarb NPK needs shift at each growth stage. Balanced feed for new crown divisions at planting during the Seedling phase, then remove flower stalks immediately; continue regular feeding once flowering begins.
NPK by Growth Stage for Rhubarb
| 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 feed for new crown divisions at planting |
| Vegetative | 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 | Annual spring feeding as new growth emerges |
| 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 | Remove flower stalks immediately; continue regular feeding |
| 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 | Fall compost mulch to build soil for next season |
When Should You Fertilize Rhubarb?
In zone 3, start fertilizing rhubarb in May. In zone 8, begin as early as March. Apply every 8 weeks through the growing season.
Which Zones Can Grow Rhubarb?
Rhubarb grows in USDA zones 3 through 8, spanning a 6-zone range.
Fertilization Start by Zone
| Zone | Start Month |
|---|---|
| Zone 3 | May |
| Zone 4 | April |
| Zone 5 | April |
| Zone 6 | March |
| Zone 7 | March |
| Zone 8 | March |
What Are the Best Fertilizer Products for Rhubarb?
Look for products with an NPK close to 10-10-10. Espoma Garden-tone is the most popular choice among home gardeners for rhubarb.
- Espoma Garden-tone
- Miracle-Gro All Purpose
- Dr. Earth Vegetable Garden Fertilizer
Prices vary by retailer and region. Check current pricing before purchasing.
Container and Raised Bed Adjustments for Rhubarb
Rhubarb can grow in large containers (15+ gallons) with spring and fall balanced fertilizer applications
Common Fertilizing Mistakes with Rhubarb
- Harvesting too heavily in the first two years weakens the crown and reduces future yields
- Allowing seed stalks to develop diverts energy from producing edible stalks
- Growing rhubarb in warm climates (zone 9+) without sufficient winter chill stunts the plant
Tips for Fertilizing Rhubarb
- Apply composted manure or balanced fertilizer in early spring as buds break dormancy
- Remove flower stalks immediately; flowering diverts energy from stalk production
- Do not harvest stalks the first year; light harvest the second year to build crown strength
Organic Fertilizer Alternatives for Rhubarb
Sources
Source:Clemson University ExtensionLast updated: