A bulb is any plant that stores its entire life cycle in an underground storage structure, which is the common bulb shape, according to the University of Illinois. Bulbs are generally perennial plants that have a long period of growth. Bulbs then go into a period of dormancy to conserve energy.
True bulbs bulbs have five major parts: The basal plate at the bottom of the bulb where the roots grow; the fleshy scales that store the nutrients; the shoot; the tunic, which covers the scales; and the lateral buds, which develop from the main shoot. True bulbs are divided into two subdivisions called the tunicate bulbs and the imbricate bulbs. Tunicate bulbs have a paper-like tunic. The imbricate bulb does not have a tunic to protect the scales, but is still considered a true bulb.
Tubers are bulbs that do not have the basal plate at the bottom of the bulb where roots grow and does not have a tunic covering the scales. The tuber surface has buds scattered about its surface that develop shoots and roots. The tuberous root contains the nutrients for the plant.
Bulb hardiness, says the Purdue University Extension, determines at what time of the year the bulb should be planted. Bulbs are considered hardy when they can survive winters planted in the ground. Hardy bulbs should be planted in the fall. Tender bulbs require removal from the soil during the dormant period and are placed into storage to prevent damage. Tender bulbs are planted in the spring.
Bulbs require good site preparation to grow properly. Good soil drainage is required, so tilling the soil is recommended to break up compacted soil. During this time, organic matter such as compost or yard waste should be added to the soil to improve structure. According to the University of Illinois, organic matter should be worked into the top 12 to 18 inches of soil.
Spring and summer bulbs require an application of phosphorous to encourage root development from the bulb. Phosphorous, because of its stability in soil, will not move. It must be buried slightly under the area where the bulb is buried so it is used by the bulb roots. A complete, water-soluble fertilizer, such as 5 tbsp. of 10-10-10 fertilizer and 2 cups of bonemeal per 10 square feet will suffice.