Bulbs, Rhizomes and Corms

Cooler weather has arrived and most of you gardeners have put away your hoes and rakes for the winter. You may want to get them back out, however, for there is one more task you should consider; that is, if you love the smiles and sparkles of spring-flowering bulbs. This month, consider planting some bulbs or similar structures for spring color.

A wide variety of bulbs grow well in Georgia. Some are grown as pot plants for their flowers, while others are used in shrub borders, naturalistic plantings, and in large beds en masse. Now is the time to plant most of them for that splash of spring color we all look forward to so much. Daffodils, tulips, hyacinths, and hybrid lilies are examples of true bulbs which can be planted in October.

What are bulbs? Strictly speaking, bulbs are specialized underground organs consisting of a flower bud at the top enclosed by thick, fleshy scales. Inside bulbs are the makings of whole new plants: roots, stems, and leaves.

Other underground structures, such as corms, tubers, tuberous roots, and rhizomes are referred to as bulbs, but are not true bulbs. They are actually modified stems or roots. What true bulbs and these structures have in common is their primary function, which is to store food during adverse conditions such as the cold of winter.

Corms are compressed stems surrounded by dry, scale-like leaves. Common examples are gladiolus and crocus. Corms differ from true bulbs in that they have distinct nodes (points from which new stems grow) and internodes (distances between nodes). Cormels are small corms which form at the base of an old corm. Glads should be planted in late spring for the summer garden.

Tubers are modified stems which develop on underground stems. Irish potatoes and caladiums are good examples of these. Tubers have nodes too; in fact, they are the “eyes” on a potato.

Sweet potatoes and dahlias produce thick, fleshy underground roots called tuberous roots. Tuberous roots have the same internal structure as true roots.

Rhizomes are stems which grow horizontally at or just below the surface of the soil of such plants as bearded irises, canna lilies, and lilies of the valley. Rhizomes have the same internal and external structure as true stems.

Its bulb time! Spring-flowering bulbs will soon begin to flood the market. Full color posters and catalogs will offer gardeners enticing glimpses of what their landscapes can be if planted enmasse. I have received more than one of these catalogs myself. Here are the answers to a few frequently asked questions about spring-flowering bulbs.

Q. What spring-flowering plants are often grown from bulbs planted in the fall?

A. The most commonly grown in the middle Georgia area are tulips, hyacinths, daffodils, and crocus.

Q. When should spring-flowering bulbs be planted?

A. Bulbs should be planted in the fall. In most areas of Georgia, this is anywhere between mid-September and mid-December; however, October is generally considered the ideal time to plant. Fall planting is important for this reason- the natural chilling the bulb receives provides the stimulus for proper flower bud development and proper root formation.

Q. How deep should bulbs be planted?

A. As a general rule, planting depth should be, from top of bulb to soil surface, two to three times the greatest diameter of larger bulbs, and three to four times the diameter of smaller bulbs.

Q. When do spring-flowering bulbs bloom?

A. Bulbs bloom, of course, in the spring; however, spring is not a precise time, and it actually extends over a period of weeks. Depending on species, variety, and temperature, bloom may occur from late January to May. Daffodils, for example, often begin flowering in late January here in middle Georgia.

Q. When is the best time to dig and divide spring-flowering bulbs?

A. They can be dug and divided any time after the foliage dies and before new root growth begins in the fall. It is probably best to do this just after the foliage matures and easily separates from the bulb.

Remember, now is the time to start thinking about and ordering spring-flowering bulbs!

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507 or timlewis1@windstream.net.

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