University of Illinois Extension


Sharon A. Yiesla
Unit Educator, Horticulture
Lake Unit

Past Issues

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The Other ‘Bulbs’

When you say the word ‘bulb’ to someone, they most likely think of tulips, daffodils or some other hardy spring bulb. There is another group of fascinating ‘bulbs’ that give color to our gardens in the heat of summer, the so called ‘summer’ or ‘tender’ bulbs. Tender bulbs include begonia, caladium, canna, dahlia and gladiolus. These plants share certain characteristics; they cannot be planted outside until after the danger of frost has passed, they grow from underground structures (often called bulbs, even though most of them aren’t), they provide color in summer and they need to be dug and stored for the winter. This is where the similarities end. These plants are widely varied in their care, their flowering and their storage needs.

The tender bulbs are not new, but many gardeners have never tried them. At this time, they are starting to grow in popularity again. The ‘bulbs’ are sold in many garden catalogs and garden centers, with many varieties being offered. If you plan to try these, be aware that most of these are not true bulbs. When you buy them, expect that some of them will look quite different from the tulip and daffodil bulbs that are so familiar to us.

Let’s look at some of the plants that fall into this group:

(Tuberous) Begonias grow from an underground structure know as a tuber. The begonia tuber is concave (sunken) on the top. You should be able to see one or more buds on the top of the tuber. Plant the tuber about one inch deep, with the concave side facing up. Space the tubers about 9-12 inches apart. Since these plants cannot go outside until after the frost is over, consider starting them in pots indoors about 6-12 weeks before the last frost date.

Begonias range from 12 to 18 inches tall and come in a wide range of flower colors. They also have crisp, attractive foliage. There are some trailing type begonias available as well.

Begonias do best in partial shade. Keep the soil consistently moist, but not wet. These plants require a good supply of moisture, but don’t overdo it since they are prone to rots and leaf diseases. Avoid wetting the leaves to reduce leaf diseases.

The tubers should be dug after the first frost. Remove the foliage and clean off the excess soil. Allow the tuber to dry in the open air for a few days. Once the tubers are dry, pack them in dry peat moss or vermiculite and store them between 35 and 41 degrees Fahrenheit.

Caladiums also grow from a tuber. The buds may be very small and difficult to see. The upper side of the tuber is knobby, the lower side smoother. Be sure to plant the tubers with the knobby side up. The tubers should be planted about one inch deep and 8-12 inches apart. It is a good idea to start these plants indoors about 6 weeks before the last frost date. They will not start growing until the soil temperature is at least 60 degrees Fahrenheit. Find a warm place in the home to start them. These are more challenging to grow than some of the other tender bulbs.

Caladiums are grown for their foliage, not their flowers. They have beautiful leaves in mixtures of green, pink, red and white. Plants will range from 12-24 inches tall, depending on the variety purchased.

These plants prefer partial shade, although there are some varieties available that can tolerate more sun. Keep the soil evenly moist, but not wet. Do not put these plants into the soil outside until danger of frost is past and the soil temperature is above 60 degrees. The tubers can rot if the soil is cold and wet.

The tubers should be dug in fall as the leaves lose their color. Do not wait until after frost to dig as these plants are very cold sensitive. Remove the foliage, clean the tubers and dry them in the open air for a few days. Once the tubers are dry, they can be packed in dry peat moss or vermiculite. The tubers should be stored between 70-75 degrees Fahrenheit.

Cannas also grow from rhizomes. Plant the rhizomes in a horizontal position, about 3-4 inches deep and 18-24 inches apart. Cannas are fairly fast growing and may not need to be started indoors. If you choose to start them indoors, do so about 3-4 weeks before the last frost date.

There are many varieties of canna available and they range in height from 2 to 7 feet tall. All cannas have beautiful flowers and many have interesting foliage (stripes and colors). Flower color ranges from pink and red to yellow and orange. There are also some bi-colored flowers.

Cannas prefer full sun. They make their best growth in a rich soil with a good supply of moisture. Dig the rhizomes in fall after the first frost. Remove the foliage and clean the rhizomes. Let them air dry only for a day or two. Store them in dry peat moss or vermiculite at 41-50 degrees Fahrenheit.

Dahlias grow from a tuberous root. This is an enlarged root, with a bud at the top. There are numerous types and varieties of dahlia. They range in height from 12 inches to 8 feet. There is a wide range of flower types, sizes and colors. Before getting started with these plants, you may want to learn more about them. Check at your local library or book store for good books about dahlias.

The dahlia should be planted so that the bud is planted just above the soil level and the enlarged roots are below ground. Spacing will depend on the ultimate height of the plant. Dahlias that reach 3 feet tall or less, should be spaced about 2 feet apart. Those taller than 3 feet, should be spaced 3 feet apart. Dahlias usually need to be staked, due to the height they attain.

Dahlias prefer full sun and a consistently moist soil. Dig the tuberous roots after the first frost. Cut off the tops, leaving a 3-4 inch section of stem attached. Clean the tuberous roots and dry them. Pack them in peat moss or vermiculite and store them at 35-50 degrees Fahrenheit. The packing material can be very slightly moist to reduce shrinkage of the tuberous roots.

Gladiolus grows from a corm, which looks very much like a traditional bulb. Plant the corm with the pointed end up. Plant the corms 4-6 inches deep and space them about 3-6 inches apart.

These plants range from 1-5 feet tall, depending on the variety selected. They come in an extremely wide range of colors.

Gladiolus prefers full sun. Keep the soil evenly moist, but not wet. Protect these plants from wind and expect that they will need to be staked. Dig the corms after the first frost. Cut the stems off just above the corms. Clean the corms and allow them to dry for about a week. Store the corms in open mesh bags or in slotted trays, with good air circulation at 40-45 degrees Fahrenheit.

June - July 2002:

Prevent Mustard from Setting Seeds
Plant a Buddleia for a Great Display
| June Means Roses
The Other 'Bulbs'

Past Issues

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