Spring Bulbs: To Fertilize or Not to Fertilize

by Gail Anderson, IGC Horticulturalist    

For years, experts recommended putting fertilizer in each hole as you planted spring flowering bulbs in the fall. Now some bulb gurus say you don’t need fertilizer when planting bulbs.

The traditional recommendation was to use bone meal, super phosphate (now available only as rock phosphate), or Bulb Booster fertilizer (9% nitrogen, 6% phosphorous, 6% potassium) in the bottom of the planting hole. Now experts point out that the bulb already contains the food it needs to produce first season’s flowers and foliage. And animals love to dig up bulbs planted with bone meal. At Long Hill, the Trustees of Reservations garden property in Beverly, we have planted hundreds of bulbs without fertilizer in the holes.

It’s more important, some experts say, to top dress the bulbs after they have bloomed the first year while their leaves are still green. After bulbs have bloomed and after you have deadheaded them, Deb Lambert at Corliss recommends sprinkling rock phosphate on the soil around the bulb foliage. Then scratch it into the soil with a three-pronged hand cultivator. This promotes root and bulb development. The spring top dressing is even more important, she says, than planting the bulbs with amendments. However, she does recommend amendments both at planting and in the spring.

So, it appears, fertilizing at planting time becomes a personal decision.

Tips for Spring Flowering Bulbs

•  Purchase bulbs now for best selection.

Keep them cool (but not below 32 degrees) and dry until you plant them.

• Select only large, firm bulbs.

Squeeze them to be sure. Beware of blemishes, soft spots, or wrinkled outer skin. If the bulb is about to split (common with daffodils) be sure each section seems large enough to support a flower stem.

• You can plant bulbs as late as December 1,

providing the ground has not frozen. Bulbs need a minimum of 11 weeks of chilling in order to perform properly.

• Plant bulbs 2-3 times their depth.

If a bulb measures 3 inches top to bottom, the planting hole should be at least 6 inches deep.

• Plant in average to rich soil with good drainage.

If needed, add organic matter to enrich the soil. Add sharp sand to increase  drainage.

·      Plant bulbs in full to almost-full sun.

Bulbs planted in the shade do not rejuvenate well. Bloom diminishes after the first year.

• Don’t forget minor bulbs—

snowdrop, crocus, winter aconite, chionodoxa, puschkinia, iris reticulata, etc. They bloom very early and are effective near the edges of garden beds and walks.

• If you have deer or rodents, avoid tulips.

Plant critter-resistant bulbs including narcissus (daffodils), allium, crocus, chionodoxa, puschkinia, scilla, hyacinth. Be aware however, that no plant is completely critter resistant.

• If you want repeat bloom in succeeding years, avoid tulips.

Daffodils (narcissus) are fairly reliable repeat bloomers. Tulips are not good repeaters. The best repeat tulips are the Darwin type.

• Plan for a succession of blooms.

Plant early, mid, and late flowering bulbs in the same area. Some garden designers plant large bulbs, then fill the hole halfway and plant minor bulbs over the top.

• Plan to hide the dying bulb foliage.

Consider planting bulbs amongst perennials, so the emerging perennial foliage will mask the dying bulb foliage. Never cut bulb foliage until it is completely brown.

• Consider a naturalistic random pattern with unequal spacing.

This is effective unless you have a very formal setting, At Long Hill we scatter bulbs by hand and plant where they land.

• Or plant several bulbs in one hole.

This saves time and provides a more concentrated show of flowers. However, the overall design will be more “spotty.”

• Plant bulbs fairly close together.

Deb Lambert recommends spacing equal to the diameter of the bulb, i.e., 6-inch spaces between 6-inch-diameter bulbs and 3-inch spaces between 3-inch bulbs. Do not plant bulbs so they touch each other or there will not be enough root room.

• If there are few existing bulbs in your garden, plant one area.

This is especially true if you have budget or time constraints, You will have a better show of blooms in a small space than if you plant a few bulbs throughout the garden. In succeeding years, plant other small areas.