Spring-blooming bulbs are usually planted in the fall and left to fend for themselves throughout the winter. The bulbs generally come with planting instructions for how deep to bury them and how much sun exposure they will need, but when and whether to feed the bulbs is often missing.
Those big fat bulbs represent all the energy and food the plants have stored up for the next year’s blooms. When you plant spring-blooming bulbs in the fall, the only thing they need to do during the winter is send down some new roots. To help the bulbs do this, you should feed newly planted bulbs with a balanced fertilizer and bonemeal that is high in phosphorous. While you can use 10-10-10 and bonemeal, there are fertilizers sold as "bulb food" that contains superphosphate or bonemeal.
Phosphorous isn’t good at working its way down through layers of soil. To be effective, it needs to be added to the planting hole or worked into the surrounding soil before you plant, rather than just sprinkled on top.
Do I Need to Fertilize Every Type of Spring Blooming Bulb?
If the bulbs are going to be maintained in a planting bed for more than one year, it is important to supply additional fertilizer. Bulbs that will be dug up after they bloom do not need any additional fertilization after the foliage dies back.
As the bulbs grow in the spring, their storehouse of food and energy is all expended and the bulbs need to produce and store more. The most important thing you can do for your bulbs in the spring is to let the foliage grow as long as it can. Do not prune, cover, or braid the leaves. This is how the bulbs feed themselves. You can cut off the flower stalks if you like. If you planted bulbs that naturalize, it’s best to leave the flower stalks on and let them set seed.
When to Fertilize Established Spring-Blooming Bulbs
Established bulbs should be fed in the fall by mixing five tablespoons of 10-10-10 soluble fertilizer with two cups of bonemeal. This will cover a 10-square-foot area of planted bulbs. Sprinkle the mixture onto the soil and use a hand rake to work it into the soil. This should be done before any winter mulch is applied. An equivalent amount of "bulb food" can be substituted for the mixture. Read the product's label instructions to ensure that you are using the correct amount.
The process should be repeated in the spring for established bulbs as soon as the first shoots break through the ground. Rake back the winter mulch and work the fertilizer into the soil. The mulch can then be put back in place to help prevent weeds. Do not fertilize the bulbs once they have started flowering.