Fertilize bulbs by applying a balanced 10-10-10 granular fertilizer to the soil surface at planting time and again in early spring when shoots emerge, but never fertilize spring-flowering bulbs after they start blooming.
Slip up on the timing and you risk bulb rot or weak flowers. The good news is that the process is simple when you follow two feeding windows. Here’s exactly when and how to apply fertilizer for new and established bulb beds.
Timing: When To Fertilize Spring And Summer Bulbs
Stick to two windows.
First application: at planting time (September through October for most spring bulbs like tulips, daffodils, and crocuses). Second application: early spring, the moment you see new green shoots pushing through the soil. For summer and fall-flowering bulbs, you can fertilize monthly from shoot emergence up to full flower. For perennial bulbs grown year after year, two feedings per season are enough.
What Fertilizer To Use And How Much
Look for a balanced fertilizer with an equal ratio of nitrogen, phosphorus, and potassium — 10-10-10 or 5-5-5 works well. Phosphorus is critical for root development and bloom formation, but it moves very slowly through soil. That’s why phosphorus needs to be in the soil before the bulb roots start growing.
Skip the bone meal.
Application rates differ for new plantings versus established beds:
| Situation | Fertilizer Amount | How To Apply |
|---|---|---|
| New planting (in rows) | Mix into soil before planting; keep out of the planting hole | |
| New planting (individual bulbs) | Work into soil around the bulb, not inside the hole | |
| Established bed (top-dress) | 4 lbs per 60 square feet | Apply to soil surface, lightly rake in, water thoroughly |
| Maximum per application | 2 lbs per 100 square feet | |
| Bulb fertilizer for established beds, pre-packaged blends | Follow label rate | Sprinkle on soil surface above the bulbs |
Thinking about upgrading your approach? Check out our roundup of the best bulb fertilizers we’ve tested this season to find a product that matches your soil and schedule.
How To Apply Without Damaging Bulbs Or Roots
For established beds in spring, apply the same way — scatter granules evenly over the soil surface around emerging shoots, water in well, and you’re done.
Soil, Depth, And The “Don’t” List
Most spring-blooming bulbs prefer a soil pH between 6.0 and 7.0. Plant bulbs deeper in northern climates and in light, sandy soils; shallower in heavy clay. Loose, well-drained soil rich in organic matter is ideal for root growth.
FAQs
Can I fertilize bulbs after they bloom?
Is bone meal still a good fertilizer for bulbs?
How deep should I plant bulbs?
Planting depth depends on your climate and soil type. In the North and in light, sandy soils, plant bulbs deeper. In heavy clay soils, plant shallower. A general rule is to plant bulbs at a depth equal to three times the bulb’s height.
References & Sources
- University of Illinois Extension. “Planting Bulbs.” General bulb planting and fertilization guidelines.
- Chicago Botanic Garden. “When to Fertilize Bulbs.” Timing recommendations for spring and summer bulbs.
- The New York Botanical Garden. “Bulbs: Fertilizing.” Fertilizer application rates and best practices.