Summer and Fall Flowering Bulbs for the Landscape

Revised 6/99 -- Author Reviewed 6/99 HIL-8632

A. A. De Hertogh, Professor
M. A. (Kim) Powell, Extension Horticultural Specialist
Department of Horticultural Science

 

Summer and fall flowering bulbs provide another dimension to gardening. They add beauty and interest to the landscape and, since most of them are tender, they offer a unique challenge to the gardener. There are a large number of different types of bulbs, offering variations in forms, fragrances, colors, and lasting brilliance which many summer annuals cannot achieve.

When choosing "bulbs," one must always be aware of a few basic terms. Not all grow from true bulbs; some grow from rhizomes (Canna), corms (Gladiolus), or tuberous-roots (Dahlia). Botanically, there is a difference, but this is generally important only to the scientist. The everyday usage of the term "bulb" includes all plants that grow from fleshy underground storage organs. The most important difference which must be understood is the distinction between hardy and tender bulbs. In North Carolina, hardy bulbs (daffodils, hyacinths, tulips, lilies) over-winter in the ground, while most tender bulbs (Gladiolius, caladiums, tuberous begonias) are either dug after the first frost or the containers are brought indoors. They are dried or placed in storage materials in either warm or cool place (see Table 1). In the spring they are either replanted after subsequently placed outside on patios, decks, etc.

When landscaping with summer and fall flowering bulbs, special attention must be given to the design. As with most annual flower beds, they are planted in late spring and usually renovated every year. During the winter months, a mulch is spread over the bare ground. Design the area to incorporate woody ornamentals which offer a landscape interest when the bulbs are not flowering. Favorite uses of these bulbs are in: borders, ground covers, rock gardens, and especially in containers and hanging baskets. Most summer flowering bulbs are not suggested for "perennializing" because they do not overwinter and they are considered somewhat "formal." Rhizomous Iris, Lilies, and daylilies are notable exceptions. The following are examples of the eight of the most popular summer and fall flowering bulbs and their cultural and storage requirements:

Caladiums are tropical plants with heart-shaped leaves ranging in size from 6 to 12 inches. The numerous cultivars offer foliage colors in red, salmon, rose, white, or green with many variegated combinations. Caladiums prefer a rich soil and shade. Grown mostly for their interesting foliage display, caladiums perform well in garden borders and containers. Fertilize them once a month with 8-8-8 (2 lbs/100 ft2). Caladiums do not overwinter in N.C. Therefore, they must be dug in the fall and stored dry at 70 to 75 °F. The tubers are replanted in the spring after the last chance of frost. One additional note: most cultivars are adapted to full shade, but many selections tolerate partial sun or early morning sunlight. Full sun generally reduces the intensity of the foliage color of most cultivars.

Cannas are popular among home gardeners and professional landscapers because of their extended flowering period and luxurious green or bronze foliage. There are over 60 cultivars available, providing a wide choice of colors. The rhizomes are generally planted the first of May in a rich well-drained soil, and in an area which receives full sun for at least 6 hours per day. Plant with only about an inch of soil over the rhizomes and set them 18 to 24 inches apart. Apply 3 to 4 lbs of 10-10-10 per 100 ft2 every 4 to 6 weeks throughout the growing season and water thoroughly. In cold areas of North Carolina (zone 6), the ground freezes and the rhizomes do not overwinter well. Once the foliage has been killed by frost, the rhizomes should be dug, shoots removed (along with any soil), and dried for a few days. They can be stored in bushel baskets or burlap bags covered with dry peat or vermiculite at 41 to 50 0F. In zones 7 and 8, they can be left in the ground, if mulched with 3 to 4 inches of organic material. .

Dahlias are generally associated with late summer to early fall flowering periods in N.C. (usually August to October). They can, however, be flowered earlier. Dahlias prefer full sun (zone 6) to partial shade (zones 7 and 8) and a rich, well drained soil. They require ample water during the summer, especially during periods of drought . Once started, be certain to keep them actively growing. Some dahlias require staking, as heights up to 7 feet are not uncommon. Flowers range from 3 to 12 inches in diameter and there are many shapes and colors available. A good pest control (insect and disease) program will enhance the success of dahlias. They are excellent as fresh cut flowers for the homeowner. Dahlia clumps are generally dug in the fall after the first frost and stored at 35 to 45 0F in dry vermiculite or sand. In the spring, clumps can be divided with each section having at least one shoot. It should be noted that seed grown dahlias are not very heat tolerant. Also, they tend to lack uniformity in growth habit and flower color display.

Daylilies (Hemerocallis -- Greek meaning "beautiful for a day") are among the most popular and easiest bulbs to grow. One can have a flower display from early on summer to frost by using average garden soil, full sun to partial shade, an early summer application of 8-8-8 fertilizer, and a range of cultivars. Some daylilies can perennialize in extreme environments e.g., poor eroded slopes with no supplemental irrigation. However, the addition of organic matter is generally recommended for landscape use, both incorporated into the rootzone area and as a mulch. Currently there are over 12,000 registered cultivars representing almost the entire spectrum of the rainbow (Pure blue and pure white are the only two colors not available.). Daylilies are excellent for use in the perennial garden as taller background plants, in naturalized settings, or even the cutting garden. Hardy through zone 3, daylilies are adapted to all regions of N.C. and do not require winter storage. Propagation is usually by division of clumps either in the fall or early spring using plantings that are 2 to 3 years old. Each clump should have 3 shoots with an adequate amount of fibrous roots. They range in height from 12 inches to 4 ft. The flowers are borne on a leafless stem called a scape.

Gladiolus are a gardener's delight because they are easy to grow and offer a wide spectrum of colors. When planting times are staggered (weekly), they will flower over the entire summer. Corms can be planted outdoors starting in early May. Planting depth to base of the corms is 4 to 6 inches. Use a well-drained soil and plant them 6 to 8 inches apart. Many gardeners like to plant in rows -- if so, the rows should be approximately 36 inches apart. A slow release fertilizer (5-10-10) should be applied at the rate of 3 to 4 lbs per 100 ft2 of bed area when plants are 6 to 8 inches tall, and again when the flower spikes begin to appear in the foliage. Most Gladiolus do not overwinter. Therefore, the corms must be carefully dug and stored. After the foliage has dried, dig the corms, remove the soil, and cut off dead tops. Dry corms for 3 or 4 days in an open area and dust with an insecticide and fungicide. Store dry in mesh bags or trays at 35 to 41 0F.

Lilies (Lilium spp.) are excellent bulbs for the summer garden. There are about 80 species and several hundred cultivars available. They range in height from 2 to 8 ft. They are available in white, yellow, red, pink, orange, maroon, and various bicolors. They require a well-drained area that receives plenty of sunlight and need to be kept moist. They can be planted either in the fall or spring. Either time is satisfactory; it only depends on the availability of the bulbs. Space them 6 to 10 inches apart. With the exception of Lilium candidum (Madonna Lily), which should be planted with only 1 inch of soil covering the bulb, lilies should be planted with 4 to 5 inches of soil covering the bulb. This allows them to form stem roots. Tall lilies may need to be staked and should be protected from high winds. For most lilies, the pH should be about 6.5. Fertilize them lightly on a monthly basis with 5-10-10 starting when the shoots begin to emerge. Lilies perennialize readily and generally do not need to be disturbed. Aphids and thrips can be pests.

Rhizomatous Iris (Iris spp.) are one of the easiest to bulbous plants for the garden. There are many species including: Yellow Flag Iris, Siberian Iris, Blue Flag Iris, Japanese Iris, Crested Iris and Black Iris. There are 6- to 8-inch dwarf types and 3- to 4-ft tall types. They come in all colors (solid and bicolors) except red. Most species require a well-drained soil and only an occasional fertilization. They can be planted in the fall or spring depending on the availability of the rhizomes. Plant them with 1 to 2 inches of soil covering the rhizomes. They grow best in full sun, but do quite well in light shade. Rhizomatous Iris tend to grow and perennialize rapidly and they need to be separated every 4 to 5 years.

Tuberous Begonias are one of the most spectacular of the summer flowering bulbs. Colors range from soft pastels to brilliant and electric solid colors. They can be used as bedding plants, in hanging baskets, or simply as flowers around trees in home lawns. Tuberous begonias are somewhat temperamental because they do not tolerate stresses. They dislike strong winds and require good air drainage. They need to be well watered, but do not like moisture on the foliage. They don't flower well in either full sun or dense shade if not properly watered.

Incorporate a rich, organic loam into well-drained topsoil. Plant the enlarged hypocotyls (also called tubers) after the last chance of frost. The top of the hypocotyl should be at soil level. Place containers in partial shade. Water when soil shows signs of drying, preferably in the morning hours. Storage procedure requires digging after frost has killed foliage, drying for a few days in open area, then storing in dry peat moss at 35 to 41 0F. They can also be stored in containers or hanging baskets.

Partial list of summer and fall flowering bulbs for North Carolina.

Name

Storage Organ

Light Exposure

Habit

Storage Condition

Achimenes

Scaly rhizome

Partial sun

Low trailing

Keep rhizomes in pots indoors at 60 to70 0F during winter.

Acidanthera

Corm

Full sun

2 to 3 ft

Store in dry area with ventilation at 60 to 70 0F.

Agapanthus (Lily-of-the-Nile)

Rhizome

Full sun

2 to 5 ft

Zone 6, bring plants indoors in containers.

Alliums

Bulbs

Full sun

10 in. to 5 ft

Not necessary

Amaryllis belladonna (Naked lady)

Bulb

Full sun

2 to 3 ft

Not necessary

Anemone coronaria

Tubers

Full sun

2 to 15 in.

Store in dry peat moss at 50 to 55 0F.

Begonia, Tuberous

Hypocotyl (Tuber)

Partial shade

12 to 18 in.

Store in dry peat at 35 to 41 0F.

Caladium

Tuber

Light to medium shade

12 to 20 in.

Allow to dry, then store 70 to 75 0F

Canna

Rhizome

Full sun

2 to 7 ft

In zones 6 and 7 store in dry peat or vermiculite at 41 to 50 0F. Mulch in zone 8.

Colocasia esculenta (Elephant's ear)

Tuber

Full sun

3 to 6 ft

Allow to dry, then store in 70 to 75 0F, dry area.

Convallaria (Lily of the-valley)

Rhizome

Partial shade

8 to 10 in.

Not necessary

Cyclamen (Hardy spp.) (not the florist type)

Hypocotyl (tuber)

Partial shade

3 to 12 in.

Not necessary

Dahlia

Tuberous root

Full sun

1 to 8 ft

Store in dry vermiculite or sand at 35 to 45oF. Overwinter in zone 8, mulch in 7.

Eucomis (Pineapple lily)

True bulb

Full sun

1 1/2 to 2 ft

Grows well outdoors in zones 7 and 8. Overwinter inside in container in zone 6 at 55 to 68 0F.

Gladiolus

Corm

Full sun

1 to 5 ft

Dig when foliage dies down; air circulation is essential. Dust with insecticide and fungicide and store in mesh bag at 35 to 41 0F.

Gloriosa (Climbing lily)

Elongated tuber

Filtered sun

Climbing to 6 ft

Store in dry peat moss or sand at 50 to 60 0F. Can overwinter in Zone 8 with a mulch.

Hemerocallis (Daylily)

Tuberous root

Full sun/light shade

1 to 3 ft

Not necessary

Iris, Rhizomatous

Rhizome

Full sun/light shade

1 to 4 ft

Not necessary

Liatris

Corm

Lt. shade

2 to 4 ft

Not necessary

Lilium spp. and cvs.

True bulb

Full sun

1 to 7 ft

Do not need to be lifted. If stored, place bulbs in peat moss at 32 to 35 0F.

Scadoxus (Blood lily)

True bulb

Light shade

10 to 24 in.

Bring containers indoors and grow at 50 to 58 0F.

Zantedeschia (Calla lily)

Rhizome, tubers

Full sun

1 to 4 ft

Store in pots indoors at 50 to 60 0F. Can overwinter in Zone 8 with a mulch.


Published by

North Carolina Cooperative Extension Service


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