What are commonly known as flower bulbs encompass a wide array of underground storage bodies that hold plant DNA and nutrients. These include corms, tuberous roots, swollen hypocotyls, rhizomes, tubers and true bulbs such as tulips. Upon close visual and touch inspection, you can readily determine the general health of a bulb but its performance cannot always be guaranteed.
Inspect the skin and/or coating of the bulb to make sure that it is attached or if gone has not resulted in drying or disease damage to the bulb. Bulbs with missing, gouged or abraded skin have been mishandled and, though they may be alive, they are weakened and therefore not ideal for planting.
Look at and feel the surface of the bulb to make sure it is plump for its size, seems hydrated and is relatively smooth without holes, breaks or dings. A shriveled or shrunken bulb is likely not viable.
Hold the bulb in your palm to see if it feels large for its type and if it feels heavy in the hand for its size or oddly light for its size. Healthy bulbs are dense with moisture and nutrients and weigh comparatively more than an unhealthy bulb of the same variety and size. Unhealthy or dead bulbs feel light for their size or are comparatively small for their type.
Survey the bulb for any signs of disease, mold or mildew. Healthy bulbs are firm and not soft and mushy when pressed lightly. Look at and feel the root plate at the bottom of the bulb. It should be firm and free of any lesions.