Dig up flower bulbs, allowing several inches around each plant to avoid accidentally cutting into the bulb. Gently hose off the bulbs and dry them for several days in a single layer on newspaper. Discard any bulbs that are rotten, diseased or showing insect damage, and place remaining bulbs in cardboard boxes or plastic bags into which ventilation slits are cut. Label the containers, loosely packing them with vermiculite or dry sand. Regularly check stored bulbs, eliminating any rotten ones.
Spring-flowering bulbs, such as tulips, daffodils, crocuses and hyacinths, are considered winter-hardy and are not dug at the end of the growing season. They require cold to ensure that they bloom the following spring. Semi-hardy bulbs, such as paper whites, anemones and ranunculus, need not be dug in areas where winters are mild but must be dug and stored in climates where winter temperatures dip near zero. Calla lilies, dahlias and tuberous begonias are considered tender bulbs that cannot survive frost conditions and are usually dug and stored to preserve them.
When storing bulbs, pack them into containers as they are planted, with roots on the bottom and stems pointing up, allowing some space between bulbs to prevent rot. Cover loosely with wood shavings, peat moss or other light-weight packing medium. Most semi-hardy and tender bulbs benefit from storage in a cool, dry place that remains above 32 degrees Fahrenheit until after the last winter frost.
It's often best to leave tender bulbs undisturbed when planted in a pot or other container, moving the container inside or to a suitably warm spot in the garage until springtime.