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Feeding Time for Bulbs
Nutrients for Bulbs
Most gardeners fertilize spring bulbs as they plant in autumn, adding 4-10-10 formulated fertilizer beneath the bulbs, then covering the fertilizer with soil before they place a bulb into each hole.
This low-nitrogen fertilizer helps the bulbs develop their roots and gain energy over the winter to produce shoots, stalks and flowers.
After the nutrients that were provided at planting are gone, give bulbs supplemental fertilizer so they grow, stay healthy, and produce more flowers.
Fertilize bulbs left to naturalize or overwinter in the soil by watering in 10-5-5 fertilizer for spring bulbs and 10-10-10 fertilizer for summer and autumn bulbs after their shoots begin to emerge.
Fertilizer applied when you prepared the soils to plant your beds or containers will give your bulbs all the nutrients they need to get them off to a good start [see: Preparing Soil for Bulbs].
Once they fade after flowering—or are about to begin a second or subsequent season—you’ll need to fertilize them again with a seasonal feeding.
Fertilize bulb plantings in their second and subsequent seasons when flower spikes emerge.
Seasonal feedings provide bulbs regular applications of nitrogen, phosphorus, and potassium, plus micronutrients and trace minerals. All these are essential for root and foliage development, bloom development, and flowering, as well as to maintain vigor and health.
Strong, healthy bulbs shrug off most pests and plant diseases [see: Bulb Pest and Disease Solutions].
Applying Fertilizers to Bulbs
Before you apply fertilizer to your bulb plantings, always read completely and follow exactly all the package directions for each fertilizer.
Use a hand fork or a garden rake to work in granular fertilizer after it’s applied. Mix it into the top few inches of soil.
For beds with mulch, rake the mulch aside in sections, apply the fertilizer, then work it in.
Water thoroughly immediately after you apply the fertilizer. This helps dilute, dissolve and spread the nutrients that it contains. Mixing, spreading and diluting prevents foliage and root burn.
Take safety and health precautions when applying fertilizers. Wear gloves, eye protection, and protective clothing. Safely dispose of empty containers and unused fertilizer as directed. Wash protective clothing separate from other laundry.
Spring-Blooming Bulbs
Choose from one of three options for feeding spring bulbs, applying fertilizer monthly until the bulbs’ buds begin to open:
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- A 10–5–5 dry or granular fertilizer worked into the soil surface.
- An enriched organic compost worked into into the mulch over the soil.
- A foliar fertilizer sprayed onto foliage or flower buds and absorbed directly.
Summer- or Autumn-Blooming, and Evergreen Bulbs
Choose from one of three options for monthly fertilizing of other bulbs, applied during periods of active growth until the flower buds form, then stopped:
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- A balanced 10–10–10 dry or granular fertilizer worked into the soil surface.
- A liquid organic fertilizer applied as a drench.
- A foliar fertilizer sprayed onto foliage or flower buds and absorbed directly.
Other Fertilizer Considerations
Avoid predormancy feedings. It’s best instead to apply a fresh layer of protective mulch to the bed that will decompose slowly, release its nutrients into the soil and be available for the bulbs when they begin to grow new roots and foliage.
For naturalized beds with bulbs that remain in place from season to season, withhold water beginning in autumn. In spring, or when shoots or flower stalks first emerge, apply a 0–10–10 formulated liquid fertilizer and immediately water to carry it deeply into the soil.
Phosphorus and potassium quickly bind chemically to soil mineral particles. They remain at the surface, unavailable to your bulbs’ roots.
Watering helps carry these non-water-soluble nutrients down to the bulbs.
Other Soil Care
If the bed can be cultivated and the location of the bulbs is certain, cultivate carefully around the plantings to mix any applied fertilizer into the soil.
Annually in spring, give your soil a boost, especially for bulbs planted in containers. Decomposed kelp extract contains few nutrients but holds many enzymes that foster root development and activate growth points on bulbs.
About Predormancy Feedings
Except in rare cases, it’s a myth that spring bulbs need predormancy fertilizing. One exception, however, is plantings in beds of naturalized bulbs that are never lifted except when they become overcrowded.
Fertilize such beds in the autumn after the first frost with a 0-10-10 formulation to avoid nitrogen prompting unwanted growth and allow cold temperatures to keep the bulbs dormant. They’ll develop roots during the last days of winter, using the nutrients provided in autumn.
This mimics natural bulb habitats, including woodland settings with fallen leaves that decompose over winter.
For most other bulbs, it’s more important to leave the bulbs’ foliage in place after they finish their bloom.
Growing leaves manufacture nutrients the bulbs store underground and use to grow new bulbs, corms, or tubers. The payoff for leaving foliage in place comes the following season. Trim away spent seed pods and flowers after bloom, but leave the foliage to do its work.
After a month or so passes from the last blooms, all the foliage will yellow and wither. It can be safely removed and composted.
Step-by-Step Instructions
Fertilizing Bulbs at Planting and Seasonally
Bulbs lifted from their beds after they bloom require fertilizing only at planting and after active growth begins.
Use lifting, however, as an opportunity to cultivate your soil and work in amendments for the following season [see: Preparing Soils for Bulbs]. Remember to fertilize as shown when you remove them from storage and replant them the following year.
Naturalized bulbs should receive a seasonal feeding as they begin their growth cycle.
Gather the appropriate fertilizer, a shovel, a rake or hand fork, and gloves, and follow these steps:
Fertilizing New Bulb Plantings
Use 4–10–10 granular fertilizer or fertilizer formulated as bulb food but free of the ingredient bone meal. Apply as directed on the package to the bottom of planting holes, trenches, or beds that are 3–4 in. (75–100 mm) deeper than the recommended planting depth for the bulb species.
Use a hand fork or rake to thoroughly mix the fertilizer granules into the soil at the bottom of the planting hole, trench, or bed.
Fill with native soil in a layer 3–4 in. (75–100 mm) to cover the amended soil. This layer helps prevent direct contact between the bulb and the fertilizer. Set your bulbs into the soil, pointed side up and basal-plate side down. If the bulb’s shape and form is unclear, lay it on its side. Fill the hole, trench, or bed with soil and compact it firmly.
Seasonal Fertilizing of Bulbs
When soils are workable in spring, but before sprouts appear, carefully rake away mulch covering the bulbs. Wait until the bulbs’ sprouts come up before continuing.
Choose 10–5–5 formulation granular fertilizer for spring bulbs and 10–10–10 for summer bulbs. Scatter the fertilizer around the base of the plants, but avoid contact with their foliage to prevent leaf burn.
With a hand fork or rake, mix the fertilizer granules into the soil surface. Thoroughly water to dissolve the granules and carry their nutrients into the soil and down to the bulbs’ root zone.
Rake existing organic mulch back into place or apply new mulch around the plants. Mulch conserves water, insulates the soil from heat or cold, and helps control sprouting weeds. It also decomposes, releasing nutrients to feed the bulbs.