The term "bulb" is used by most people to refer to plants that have underground, fleshy storage structures. Only some of the plants commonly called bulbs actually are bulbs. The definition of a bulb is any plant that stores its complete life cycle in an underground storage structure.

The primary function of these underground storage structures is to store nutrient reserves to ensure the plants' survival.

Bulbs or bulb-like plants are usually perennials. They have a period of growth and flowering. This is followed by a period of dormancy where they die back to ground level at the end of each growing season. For spring bulbs, the end of the growing season is in late spring or early summer. Spring bulbs start to grow again in the fall and flower the following growing season.

Bulbs can be broken down into five types of storage structures. These include: true bulbs, corms, tubers, tuberous roots and rhizomes. A sixth category of fleshy roots has been added here for the purpose of showing the structure. Daylilies and peonies, which are popular plants with gardeners, are examples of this type.


True Bulbs


The true bulb has five major parts. It contains the basal plate (bottom of bulb from which roots grow), fleshy scales (primary storage tissue), tunic (skin-like covering that protects the fleshy scales), the shoot (consisting of developing flower and leaf buds), and lateral buds (develop into bulblets or offsets).

True bulbs are divided into tunicate bulbs and imbricate bulbs. A tunicate bulb has a paper-like covering or tunic that protects the scales from drying and from mechanical injury.

Good examples of tunicate bulbs include: tulips, daffodils, hyacinths, grape hyacinths (muscari), and alliums.

Many plants such as daffodils form new bulbs around the original bulb. These bulbs, called offsets, develop from buds within the base of the mother bulb and produce new plants. When these bulbs become overcrowded,the flowers start to diminish in size. This is an indication that it is time to dig up and divide the bulbs.

An example of the imbricate bulb is the lily. The imbricate bulb does not have the tunic (papery covering) to protect the fleshy scales.

Imbricate bulbs must be kept constantly moist before planting so they are not injured by the scales drying out.

Lilies can be propagated from bulbils that develop in the leaf axils of the plant. They can also be propagated from bulblets that develop at the base of fleshy lily scales if maintained in a moist sand medium. It will take more than one year for the bulbils or bulblets to become flower size.


A corm is a swollen stem base that is modified into a mass of storage tissue. A corm does not have visible storage rings when cut in half. This distinguishes it from a true bulb.

The corm contains a basal plate (bottom of bulb from which roots develop),thin tunic and a growing point. Examples of plants that develop from corms include gladiolus, crocus, and autumn crocus.

When gladiolus corms are dug in the fall, they should be separated into well developed corms, to be stored for replanting, and poorly developed corms that the gardener may want to discard. The newly dug corms will have cormels that are pea size formed around the top of the old corm. The remains of the old corm will be directly beneath the newly formed corms. When the corm is cleaned up and the old stem removed, the growing point of the corm will be evident. The cormels can be saved and replanted in the back of the garden until they reach flowering size.

Examples of plants that develop from corms include gladiolus, crocus, and autumn crocus.


A tuber differs from the true bulb and the corm by not having a basal plant from which roots develop and not having a protective tunic covering.

The caladium tuber has buds scattered over the tuber surface from which shoots and roots develop.

Examples of plants that develop from tubers include caladiums, oxalis and anemones, and the common vegetable, the potato. (The potato does flower.)

Tuberous Roots

The tuberous root differs from other root structures by the nutrient reserves being stored in an actual root instead of an enlarged stem.

The dahlia reproduces from buds at the top end of the root or base of the stem.

The tuberous root of a dahlia should not be divided before placing in storage in the fall but should be divided at planting time. The root should be divided into sections with an eye bearing portion of the stem left with each section of the root.

The tuberous-rooted begonia reproduces from buds on top of the round, flat tuber.


Rhizomes differ from other storage structures by growing horizontally under the surface of the soil. On some plants, this type of rooting structure can be very invasive.

The lily-of-the-valley rhizome spreads horizontally underground and produces pips which develop into new plants. This plant is increased in the landscape by digging in the fall and removing pips with developed roots for replanting.

Fleshy Roots

Plants that have fleshy roots store nutrient reserves in the fleshy roots.

Both peonies and daylilies can be propagated by dividing. The root clumps of peonies should be divided in the fall leaving at least three crown buds with each clump.

The daylily can be divided in the fall or spring into plantlets with a single fan of leaves.

The daylily has a fleshy root system with some varieties having what might be considered a rhizome type root system. Daylilies are hardy herbaceous plants with a perennial growth habit. They have clumps of rich green, smooth foliage that dies back during the winter.

Questions and Answers about Growing Bulbs

What should be done with yellowing tulip leaves?

These should be left in place until they’re almost completely yellow, about late June. Then use scissors and cut them to the ground. The leaves should be left on as long as they are green because they are making food for next year’s flowers. If the leaves are unsightly, you could tie them together loosely and plant annuals in between.

How should late-arriving bulbs be handled?

Plant them immediately. Do not attempt to carry them over until spring. Plant in an area where the soil is not frozen, such as near the foundation of your home. Be sure to mulch. Transplant to a permanent site, if needed, next summer. If you are anticipating a late shipment, you can mulch the prospective planting site to keep the soil from freezing until after the bulbs are planted. You can also force them indoors.

How often do you have to dig up hardy bulbs?

Dig up hardy bulbs only as often as you desire to move them to a new location, or when they are becoming crowded and/or flower production decreases.

How should I fertilize hardy bulbs?

The most important time to fertilize is right after the bulbs bloom. Use 2 pounds per 100 square feet of a commercial fertilizer such as 5-10-5 or 12-12-12. Work fertilizer lightly into the soil surface.

How should I protect young tulip leaves from a late, hard frost?

Don’t! The leaves are usually not damaged by temporary cold and freezing temperatures.

I received a pot of blooming tulips for Easter. How should I treat them when they’re done flowering?

You can either throw them out immediately or make an effort to rebloom them outdoors again in two to three years. It is very unlikely that they will bloom again the year after you received them. If you want to save the bulbs, cut off the flower stalks after flowering and continue to water as needed until the leaves turn yellow. Then withhold water, cut leaves back and put the entire pot in a cool (50°F), dark place until August.

In August, plant the bulbs separately outdoors. Be sure to fertilize.

How can I keep squirrels or moles from eating bulbs?

Bulbs are not usually a preferred food of squirrels, moles, mice or other rodents, but they can take a liking to them. Moles are often unfairly blamed when bulbs disappear. More often, the culprit is field mice that also use mole tunnels. They most often attack tulips, crocus and gladioli and rarely eat daffodils, alliums or colchicums.

The mouse problem is a difficult one. Sprinkling dried blood, tobacco or a similar repellent on the ground is effective only until the next rain washes it away. Owning a cat that enjoys walking through your flower beds is a very effective deterrent to rodents.

Where you are determined to try bulbs, make a small "cage" of 1/2-inch mesh screen. Place several bulbs inside, root plate down and bury the entire cage at the proper depth. Rodents won’t be able to chew through, but roots and stems can grow out.

Why didn’t my bulbs bloom this spring?

There are only a few reasons that bulbs do not flower. If the bulbs were planted last fall, dig down to see if they rotted in the soil. If they did, the planting site is poorly drained. If you don’t find the bulbs at all or see only withered green leaves on the ground, perhaps a rodent ate them.

If leaves appeared with no flowers, question the source and the storage technique. Bulbs purchased at an end of year sale may not have been stored properly and the flower bud may have been dead at the time of purchase. Before buying many bulbs on sale, buy one or two and cut them in half longitudinally to make sure the flower bud is alive. If it is brown or dried up, the bulbs will not flower next spring. This is a fair test of the quality of the remaining bulbs. If you stored the bulbs near apples or in a garage, ethylene gas may have caused the flowers to abort.

If the bulbs were planted in a previous fall, they may have received insufficient light or the leaves may have been cut back prematurely last year, resulting in insufficient food reserves to support flowering this year.

With some bulbs, including tulips and hyacinths, decline is expected after two to three years or even sooner. These bulbs are best treated as annuals in a display garden.

Which side of the bulb goes up at planting time?

Be sure to identify either the root plate and face it downwards, or last year’s shriveled flower stalk, which goes upwards. Compare with pictures or diagrams or dig up a bulbs to see which end is which.

When can I plant summer-flowering bulbs?

Plant after the frost-free date in your area to avoid damage to emerging shoots and rotting of tubers in cold soil. Many tender bulbs may be started indoors in spring.

Can dahlias planted in spring as bedding plants be saved at the end of the season?

Yes, you can save dahlia tubers from year to year. By the end of the season, bedding plant dahlias will have produced tubers large enough to dig in fall and save over winter for the next season.