The short answer is that bulbs, corms, rhizomes and tubers are different types of flower bulbs. Some are hardy and others are tender, but all act as an energy storage container for the plant that grows from them.
Hardy or Tender
Bulbs planted in the fall are referred to as “hardy” because they can withstand the winter cold. Hardy plant bulbs need the winter cold in order to produce their beautiful blooms each spring. Plant hardy flowers like iris, daffodils and crocus in the fall and enjoy their bloom in the spring.
Many varieties of bulbs are planted in the spring because they are “tender,” meaning they cannot handle cold winter temperatures and must be dug up in the fall. Dahlia is a tender bulb. Provided below are descriptions and examples of true bulbs, corms, rhizomes and tubers.
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True Bulbs. True bulbs may have a papery skin much like an onion, or they may have pull-apart portions much like an artichoke or garlic clove. Bulbs are almost round or slightly teardrop shaped. Dig up bulbs about every 4 years, separate them and replant. Not only will you increase the area of your garden, by distributing the bulbs, you give them more room to grow and gather nutrients. True bulbs and their planting depth include hyacinth (7 inches), lily (7 inches), daffodil (8 inches) and tulip (6 inches).
Corms. A corm is slightly smaller than a true bulb and will have a flat or concave bottom. Corms and their planting depth include crocus (2 inches) and gladiolus (4 inches).
Rhizomes. Rhizomes are stems that grow and spread horizontally, sometimes close to the surface. Examples of rhizomes and their planting depth include canna (6 inches), lily-of-the-valley (1 inch), iris (no more than 1 inch) and calla (6 inches).
Tubers and Tuberous Roots. Tubers have a tough skin and have eyes, much like a potato. Flowering tubers and their planting depth include anemone (1 inch), tuberous begonia (1 inch) and dahlia (6 inches).