How to Fertilize Bulbs in Your Garden

By The National Gardening Association, Bob Beckstrom, Karan Davis Cutler, Kathleen Fisher, Phillip Giroux, Judy Glattstein, Mike MacCaskey, Bill Marken, Charlie Nardozzi, Sally Roth, Marcia Tatroe, Lance Walheim, and Ann Whitman

Although bulbs store food very efficiently, you need to give them a good start at planting time for best results. Healthy soil allows the bulbs to make use of available food, and planting time is your only opportunity to get fertilizer down below the bulb.

Don’t use bonemeal to fertilize bulbs. Contrary to what some may think, modern-day bonemeal is not a good, complete fertilizer. Bonemeal used to be good back when bones were ground up fresh and had all sorts of little meat scraps and marrow attached. Now, bones are steamed, cleaned, and then ground up, so the nutritive value is less.

Additionally, gardeners in suburban and rural areas quickly learn that skunks and raccoons persistently dig up the bulbs, looking for the bones that they think are there. They don’t eat the bulbs, but you must make the additional effort of replanting the same bulb several times.
Use granular fertilizers when planting. Fertilizers come in either granular or liquid form. Granular fertilizers, composed of tiny particles that don’t dissolve quickly in water, remain in the soil longer than do liquid fertilizers — longer is better.

To apply fertilizer, first mix granular fertilizers, organic or inorganic, with the soil at the bottom of the planting holes. Adding a thin layer of unamended soil (normal, ordinary soil — fresh from the ground, without any additives) is a good way to avoid any possibility of direct contact between the basal plate and fertilizer particles — especially important with inorganic fertilizers.
Use liquid fertilizers after bulbs are established. In subsequent years, when doing so is necessary because flowering is decreasing (not because bulbs are overcrowded), fertilize spring-flowering, summer-dormant bulbs with a liquid fertilizer, which is absorbed by both a plant’s leaves and roots. This process provides a readily available, but short in duration, source of nutrients.

Use a fertilizer that’s higher in phosphorus and potash, lower in nitrogen, and apply it at half-strength when the bulb leaves are well out of the ground. Fertilize a second time after the bulbs have finished flowering. If you have the time, give a third feeding, still at half-strength, two weeks after the second feeding.
Fertilize summer flowering bulbs just as you would any other perennial in the summer garden.

Fertilizers are available to plants only when water is available to transport nutrients from the soil to the roots. If rainfall is lacking, water the bulbs as soon as you plant them.

Bulbs usually flower well the first season after they’ve been planted. Getting them to come back year after year (perennialization) can be more challenging. Deadhead (cut off) the flowers as they fade; you want the energy to go into the bulb, not into flower or seed production. Be reasonable, however. Deadheading makes sense for tulips, hyacinths, daffodils, lilies, and such, but you’d go nuts trying to deadhead crocuses and snowdrops!

After bulbs have flowered, they still have work to do as they prepare for the next year. Bulbs need their leaves to produce food to store as reserves in their underground structures. Chopping the leaves away right after the flowers fade halts food production. Keep the leaves growing as long as they’re green and healthy looking. Don’t remove them until they begin to yellow.

Don’t forget to feed your bulbs, especially those that grow when conditions are tougher. Bulbs that grow early in spring when the soil is cool and nutrients less available need a ready source of fertilizer. Use liquid fertilizer that you can water on the leaves as well as the ground.