A true bulb consists of a modified underground stem surrounded by modified leaves that contain stored food for the plant. True bulbs have scales held together by stem tissue. Hardy true bulbs usually bloom in the spring. They go into a start of rest in the summer. After a period of low temperature, they begin growing again in the fall and early winter. Tulips, daffodils, and lilies are common examples of true bulbs.
A corm is a compressed stem. It is round, solid, and somewhat flat. It contains stored food with a bud on the top. Crocus and gladiolus are examples of corms.
Tubers are swollen underground stems flattened at one end. Although tubers vary in size and appearance, all are thick, solid bulbous organs. All tubers have "eyes" or buds on the surface where new growth begins. Tubers have rough, leathery skin. Examples of tubers are begonias and dahlias.
Rhizomes are thick, swollen, underground stems. They usually grow horizontally, just below or at the soil surface. They often spread easily. Iris and lily-of-the-valley are examples of rhizomaceous plants.
Excellent drainage is critical for almost all bulbs. Bulbs will rot if the soil remains wet, especially during the dormant period. Avoid low areas or sites where water does not drain quickly. Raised beds and soil amendments should be considered to improve poor drainage areas.
Choose a site in full to partial sun with protection from hottest midday sun for most bulbs. Afternoon protection is especially important for summer-blooming bulbs. Give flowers with red pigmentation afternoon protection to keep the color of their blooms from fading.
Spring-flowering bulbs will grow well under or near large deciduous trees. This is because trees are not leafed-out when bulbs are blooming. Bulbs planted in full sun will bloom earlier than shaded plants. Planting in full sun may produce earlier blooming and may also increase the chance of frost damage to the flowers. Slightly increasing the planting depth will negate this tendency toward blooming too early.
Only buy from reputable nurseries and mail-order companies that guarantee their stock and provide named varieties. These companies do not collect from dwindling populations of wild plants. Reputable nurseries propagate their bulbs rather than gathering them from the wild. Gathering from the wild has threatened many native species, such as snowdrops and jack-in-the-pulpits with extinction. Nursery-propagated bulbs are fairly uniform in shape and size.
Choose bulbs that are heavy and feel solid. Choose the largest bulbs available. They will have the most stored energy for flowers and foliage. Avoid nicked or soft bulbs. The bulbs skin should be free of injury.
Buy early! Most bulbs grow better if not kept out of the ground too long. Lily bulbs should not be left dry or uncovered.
Plant bulbs in groups. Their splash of color is lost when they are spaced out in single rows. Work the soil well to prepare new beds for spring-flowering bulbs. The soil quality under the bulbs is especially important. Loosen the soil below the bulb planting depth. If the soil is heavy clay, mix in 1/4 to 1/3 organic matter. Add fertilizer based on soil testing.
Not all bulb-type plants are winter hardy. Those that are not must be planted in spring after the frost-free date. They then are dug in the fall and stored during winter for replanting next spring. Common members of this group include gladioli, dahlias, cannas, caladiums, and tuberous begonias.
Plant hardy spring-flowering bulbs from late August until the soil freezes. Daffodils should be planted no later than September or early October because they need a longer period for root development before the soil freezes and growth stops.