Bulb is a broad scope term for underground plant storage organs. These also include rhizomes which are underground stems designed to hold plant energy for future blooms. Corms are spreading stems which have swollen bases that store carbohydrates and produce buds on the surface of the stem. Tubers are organs which hold starchy plant food and have latent buds from off the swollen underground stem. True bulbs have a fleshy scale or layered exterior. Roots come from the hard interior called the basal plate. All these organs have the same purpose; to hold the blueprint for future blooms and provide a food reserve for initial growth.
Gardeners in temperate zones such as the Pacific Northwest do not need to pull up their semi-tender bulbs. Plants such as Gladiolus will still remain viable and bloom in successive summers. However, the hardiness scope of each variety of bulb varies and it is important to pay attention to the zonal requirements at purchase and planting time. It is advisable to leave the greenery on a bulb until it dies back so it can gather solar energy for storage. This means by the time you need to remove the bulbs for overwintering you may have lost sight of which ones need to be salvaged.
Use plant stakes or signs to mark the tender plants that will require removal from the soil for winter.
Hardy bulbs and their counterparts generally require a chilling period to force bloom. In southern and warmer states, they perform as annuals unless you remove the bulbs from the soil after bloom and provide the required chilling period. The length of this requirement varies from plant to plant but you can mimic cooler outdoor conditions by placing the bulbs in the refrigerator. Average chilling periods are from 11 to 17 weeks. Overall, hardy bulbs can remain in the ground during the winter in United States Department of Agriculture zone 8 and above. Semi-hardy bulbs fare better in a wider range of temperatures but they cannot handle a hard freeze which may crack the bulb and promote rot when soils start to thaw. Tender bulbs must not be exposed to freezing temperatures.
Lifting bulbs refers to the practice of removing them from soil and storing them in a cool, dry location that will not freeze but is not so warm it forces sprouting. The garage or cool basements create a perfect site for overwintering bulbs. Let the foliage remain as long as possible and then cut it back just before the danger of frost threatens. Dig up the bulb or other storage organ carefully with a garden fork. Do not cut into the tuber or bulb as this can invite disease and encourage insects. Let the organ dry out for a few days in a warm (60-70 degrees Fahrenheit) dry location and then gently brush off the soil. This is called curing and Gladiolus, Tigridia and Oxalis require up to 3 weeks of the process. Place the bulbs in a mesh or paper bag nestled in a cardboard box covered with dry peat moss. This keeps the bulbs warm enough but allows the flow of air over them to help prevent rot. It is a good idea to label the bags or even write directly on the bulb to note the variety and cultivar.