Corms typically have an outer papery protective layer. Even so, it’s best to keep them cool in storage (40 to 55 degrees). If shoots appear on corms prior to planting, handle them gingerly. If you break the shoot, you risk losing that year’s flowers. Once a corm is planted, as the plant grows it actually devours all the stored food in the corm, which shrivels and dies. As the plant continues to grow, it forms a new corm on top of the old one.
A gladiolus grows from a type of bulb known as a corm. A corm is a solid mass of stem tissue—not layers of tissue like a true bulb. They’re usually round and sort of flat. Both buds and roots grow from the base of the corm, which is the part that stores food for the plant. Examples of corms: gladiolus, crocus, freesia, acidanthera (African gladiolus), crocosmia.
Gardeners in hardiness zones 9 and warmer can plant freesias in the fall. In other zones, freesias should go into the ground in spring; they’ll need to be dug and stored at the end of the growing season so they don’t perish in the cold. If you don't want to dig them back up, simply start over next year with fresh bulbs (technically, they’re corms). Freesias are usually inexpensive. Plant the corms 2” deep in soil that drains easily, and give them a spot that gets sun to light shade.
You could almost mistake beautiful ranunculi for roses. If you live in USDA zones 8-10, plant the bulbs 2" deep in the fall. In cooler climates, ranunculus won’t survive the winter, so wait until spring to tuck them into the garden or containers, and expect the blooms to open in late summer. (You'll need to buy new bulbs next spring.) Plant the bulbs with the claw-shaped side facing down.
To enjoy gladiolus flowers for a longer growing season, practice staggered planting. Tuck individual corms into soil every 5 to 10 days. Be sure to leave space in your planting beds to accommodate subsequent plantings. The result will be non-stop glads all season long.
True bulbs, corms, rhizomes and tubers all have one thing in common: They each need a dormant or rest period following their time of active growth and bloom. Some bulbs need a summer dormancy (tulip); others rest in winter (canna). You can grow any type of bulb in your garden as long as you provide the right dormant period. That’s why northern zone gardeners dig tender bulbs, such as calla lily or canna—to give them a winter dormancy. Understanding how true bulbs, corms, rhizomes and tubers grow helps you to give these bulb beauties the TLC they need to thrive and blossom, year after year.
When tulips, daffodils and lilies burst into bloom, you’re probably not thinking much about the part of the plant that’s underground: the bulb. Flower bulbs are actually a type of food storage organ, a way that plants stash their homemade nosh to help fuel future growth and flowers. Many plants get lumped under the heading bulbs, including tubers, corms and rhizomes. Knowing a little about different types of bulbs can help you understand how these plants grow—and how you should handle them at planting time.