When you purchase bulbs from a nursery, everything a healthy mature bulb needs to produce a flowering plant is in the dormant bulb following its harvest by a reputable bulb grower. However, fertilizer may be necessary for the future success of bulbs that are meant to perennialize (return for several years), depending on your soil fertility.


Soil pH
It's a good idea before planting bulbs, or any other plants, to test your soil pH. You can do this simply with a soil pH testing probe. Doing so will help you to know which if any nutrients or minerals need applied to grow certain types of bulbs that might have specific pH requirements. Or you can use this information to select only bulbs that like the conditions of your soil as it is.

Fertilizer
Although fertilizer suggestions for bulbs vary between authorities, current recommendations are to mix a slow release bulb fertilizer into the top few inches of soil once a year. The NFBIC recommends fertilizing in the fall when the bulbs are putting out new roots which will readily absorb nutrients. A fall top dressing of well rotted manure or compost annually is also beneficial. If fertilizer must be applied over bulbs in the spring, try to make the application as shoots emerge (after the soil has thawed). It is not as desirable to fertilize spring flowering bulbs too close to flowering time or too long after bulbs are finished flowering. As spring flowering bulbs go dormant for summer their roots die back and cease nutrient uptake until the soil cools in the fall and starts the cycle over. Whichever product you choose, follow the recommended application rates on the package. 

Organic gardeners may choose to apply cottonseed or blood meal for nitrogen, greensand for potash (potassium) and bone meal for phosphorous. Bone meal is not a complete bulb food and modern processing methods leave it low in nutrients, so it is not recommended for use solely as bulb fertilizer.

Application
The application of fertilizer to bulb plantings is best done as a top dressing. To avoid burning a bulb or its roots, never mix fertilizer or fresh manure into the planting hole with the bulb. The high concentration of salts in some forms of nitrogen can desiccate plant tissue if it makes direct contact. The newly emerging roots on a bulb are very sensitive to these salts; death of the roots will result in bulb failure.