Some of the most beautiful garden flowers are produced from spring-planted bulbs, corms and roots. Try tropical cannas, elephant ears, heirloom lilies of the valley, dazzling dahlias, crocosmias, gorgeous gladioli and lilies. These create a coordinated progression of perennial blooms through summer and into fall.
Most familiar bulbs are planted in the fall, but many different varieties of bulbs, corms, and tubers can be planted in the spring (corms and tubers are more scientific terms for the lay-term “bulb”). Fall-planted bulbs flower in early spring—like daffodils, tulips, hyacinths, snowdrops, crocuses and grape hyacinths are among the most common.

Most spring-planted bulbs will die each winter unless they are dug up and properly stored. Others are just quick-blooming plants that can be planted in the spring to flower a few weeks later.

Site Selection

When deciding where to place spring-planted bulbs, consider exposure, soil type, color and height of flowers and time of flowering. Leafy trees produce little shade in early spring, but by mid-June, they may produce shade too dense for sun-loving plants. Soil type cannot be easily changed, but can be modified to the appropriate pH and density with fertilizer and organic materials.

Landscape design with bulbs is most effective when they are arranged in drifts or waves of the same or similar colors. When possible, buy multiples of eight to ten or more of each variety.

Planting and Culture

Quality bulbs, timing and well-drained soil are the important ingredients for a successful summer garden. Look for plump, firm bulbs that have no bruises, cuts, mushiness, mold or smell of decay. Generally, larger bulbs produce larger flowers.

Do not plant outside too early; plant summer flowering bulbs and tubers after the last frost date—usually mid-May in the Front Range. Plants often fail if planted before the soil is reliably warm. Planting too late is better than planting too early outdoors.

A general rule of planting depth is to plant bulbs two to three times their diameter (see attachment 1). They should also be about three times the bulb-diameter width apart. You may put bone meal in the hole when you plant, although this probably is not necessary for healthy bulbs.

Summer bulbs require water immediately after planting. The soil in your garden should be moist for these to grow well.

Many summer-flowering bulbs and tubers are well suited for containers and can be planted closely for a fuller look. Use a container with drainage holes and is deep enough for the bulbs. It must be large to allow the bulbs to form strong roots and anchor the bulbs. They will require frequent watering once the bulbs begin to sprout. In the fall, move the pot to a protected but unheated spot, such as the garage. Move pots outdoors in early spring.

Winter Storage

You may need to dig up your bulbs in the fall and replant the following spring. Shake off any soil and air dry for several days before storing in a cool, dry, well-ventilated location. Do not store in plastic; plants need to breathe. Pack the bulbs in sawdust, vermiculite, or perlite, and store in a frost-free location during the winter.

Selections

Caladiums are a tropical bulb grown for their showy foliage, which can be quite striking in the shade. Plant after danger of the last frost has passed. Colors range from white to red and many beautiful leaf patterns are available. They do best in shaded or semi-shaded areas well supplied with humus and moisture. After frost, bulbs are easy to lift and overwinter. Store caladiums in a cool place to replant in the spring.

Callas are available in colors ranging from white to yellow to pink. The flowers consist of a center spike with a single petal that is cut low on one side, a characteristic of the species. They produce from roots planted in the spring.

Nothing in our region creates a tropical look like cannas. There are numerous canna hybrids available. One of their greatest assets, in addition to their showy foliage, is that they bloom all summer. Prune stalks with fading flowers so that others will grow to replace them. Cannas flower in many colors, including rose, pink, yellow, red, and orange, and grow three to six feet tall. The foliage can be solid green or bronze; variegated types exist as well.

Crocosmia hybrids are available with orange, red, or yellow flowers. This South African member of the iris family is a standout—it grows in full sun in well-drained sandy loam. The hardy corm grows flowers two to four feet tall and has sword-shaped leaves. Plant the corms three inches apart and two inches deep. Crocosmia “Lucifer” can winter over if protected.

Dahlias are root plants hybridized from tubers—produced for the varieties of flowers. Blossoms are bred for size, flower, form, and color. There are twelve distinctive flower groups that have been created, offering an overwhelming choice of colors and blossom types. Dahlias are easy-care flowers and mix nicely with perennials and annuals. In addition, several varieties can be grown in containers. Dahlias come in nearly every color except blue. The typical dahlia can reach a height of six feet and requires support, usually provided by a stake driven 12 inches into the ground and six inches behind the root at the time of planting. Dahlias thrive in light, fertile, well-drained soil. If your soil is heavy, add organic material or plant in raised beds. Full sun is best, but eight hours will do. Dahlias do not tolerate frost and should not be planted if there is a chance that the shoots will freeze. (For more information, visit dahlia.org)

Elephant ear is grown for its huge ornamental leaves; the tuber is used to make poi, a popular food in the East Indies and tropical Asia, where the plant originates. Wait until a few weeks after all danger of frost is past, when night temperatures remain above 55ºF. Elephant ear loves water and will grow in continually wet sites, so plant in moist, well-drained soils that are high in organic content. Elephant ear does best with partial light to full shade, but need needs protection from hot sun and wind. Often planted as an annual, the tubers can be dug and replanted the following spring.

Gladiolus is a classic cut-flower plant. This midsummer bloomer prefers moist, sunny soil, and grows up to five feet tall, depending on the cultivar. There are over 10,000 cultivars and hybrids to choose from. It requires full sun and light, moist, well-drained soil. It comes in every color but blue and is known for its late-spring-to-early-summer flowers. Plant in the spring after danger of freezing has passed. Avoid heavy soils that stay wet. By planting corms every couple of weeks, you can ensure plenty of blooms for summer bouquets. (For more information, visit gladworld.org)

Lilies make great companions for other perennials because they can be tucked among neighboring plants to provide color and fragrance after other perennials have finished blooming. These are true bulbs that grow one to seven feet, depending on the species and hybrid. Colors range from white and yellow to deep red. While lilies are perennial, not all endure Colorado winters. (For more information, visit lilies.org)

Lilies of the valley will colonize into a spring-flowering, low-growing ground cover. These plants love cold and need partial shade to thrive. Warmth makes the rhizome sprout, so plant them as soon as possible. Note: all parts are poisonous, so use this exceptionally fragrant flowering plant with care around children and pets.
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Tuberous begonias come in colors from white through yellow and orange to deep red, with over 900 species from which to choose. Their flowers are primarily double. Plant in shade, in spring after danger of frost has passed. Begonias bloom all summer and fall. They do best in soil with high organic matter content that is kept relatively moist. Begonias are unique in that they have bright flowers, yet bloom in the shade. They can be grown right in the garden, but also will thrive in pots, planters, and window boxes. After frost, dig the root and store appropriately.

Remember that you do not have to dig up all of your bulbs in the fall. Most of us enjoy annual plants in our gardens, so do not feel that you have to store tender bulbs. Just enjoy them and compost the bulbs when they finally freeze. You can always buy new varieties next spring.

The authors have received training through Colorado State University Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  August 5, 2008