• Topics: Environmental Horticulture  | Houseplants and Flowers (MG)  | Cut Flower Production  | Bulbs (Flowers)  |  Black, Robert J  | Burch, Derek G 

Bulbs for Florida¹

Florida gardeners can choose from a wide variety of bulbous plants that will thrive and produce beautiful flowers year after year with proper care. Bulbous plants have thickened underground storage organs which enable them to survive unfavorable environmental conditions. These underground organs are usually the propagative units of the plants. Not all bulbous plants are true bulbs. Other specialized underground storage organs include corms, tubers, tuberous roots and rhizomes. As used here, the terms "bulb" and "bulbous plant" will refer to all underground storage organs and any plant which produces underground storage organs, respectively.

A true bulb is a compressed stem (basal plate) bearing a growing point or flower bud enclosed by thick, fleshy scales called bulb scales. Some true bulbs such as narcissus, amaryllis and tulip are protected from drying and mechanical injury by dry and membranous outer scales called a tunic.

Other true bulbs such as lilies are called non-tunicate or scaly because their outer scales are succulent and separate, giving the bulb a scaly appearance.

A corm is a solid mass of stem tissue with a terminal bud on top. In addition to the terminal bud, axillary or lateral buds are produced at nodes on the corm. In the event that the terminal bud should be injured, these lateral buds are capable of producing shoots. The solid stem structure of the corm is protected against injury and water loss by dry leaf bases that are similar to the tunic that encloses true bulbs. Gladiolus is a typical cormous plant.

A tuber, such as a caladium, is a thickened underground stem with many buds (eyes) on its surface. Unlike some true bulbs and corms that are covered with dried leaves or scales, tubers are covered with a tough skin.

Tuberous roots such as dahlia and ranunculus are true roots and lack nodes and internodes. Buds are present only at the crown or stem end of the root.

Rhizomes are thickened horizontal stems growing along or below the surface of the ground. Underground rhizomes of canna and calla produce roots on their lower surfaces and send shoots above ground.

Selection

Florida's climate is favorable for growing many tropical and subtropical bulbous plants. The number of bulbous plants is so great that the choice is not always simple. Cultural information for the most desirable bulbs for Florida is presented in Table 1. Bulbs listed are some of the best choices for home landscapes, and all have proven suitable for planting in some area of Florida. No attempt has been made to include all bulbs that can be grown in Florida.

Unfortunately, many of the common bulbs of northern states such as tulips, hyacinths, and some irises and lilies do not grow well in Florida. Very often these bulbs flower poorly or not at all, even in northern Florida. However, with special treatment many of these northern bulbs will grow and bloom the first year. Recovering bulbs for planting the following year is not recommended because the bulbs rarely flower again. Preplant handling and culture of these bulbs is presented in Table 2.

Selecting and Preparing the Planting Site

Bulbous plants can be used in landscapes as bedding plants for borders and flower beds or for cut flowers for indoor arrangements. In general, most bulbs thrive in a sunny location. However, some, such as caladiums, do best in partial shade. Heavy shade should be avoided because it will cause thin, spindly growth and poor foliage color and flowering.

Bed preparation is important for a successful bulb crop. A well-drained soil is the first thing to be considered. If the site does not drain properly, raised beds should be built and filled with soil that has good drainage properties. Adequate drainage can also be assured by installing drainage tiles, or digging ditches to carry water to lower ground.

Soil for a bulb bed should be tilled and amended by incorporating a 3- to 4-inch (7.6 to 10.2 cm) layer of organic matter such as peat, compost or well-rotted manure, and 1 to 1 1/2 pounds of 12-4-8, or an equivalent amount of other complete fertilizers per 100 square feet (10 m²) of bed. The amended soil should be leveled, moistened and treated with a soil sterilant to avoid harmful organisms and kill weed seed. Instructions are given in Table 1 and Table 2 for instances when a particular bulbous plant requires soil preparation that differs from that given above.

Planting

Once the site has been prepared, bulbs are placed over the area in neat rows or in naturalistic drifts for an informal garden effect. Space between bulbs varies with the species and the effect that the gardener wants. General spacing recommendations for many bulbous plants are presented in Table 1 and Table 2 . Dig holes to the recommended depth with a trowel or small shovel (Table 1 and Table 2), place bulbs in the holes with the points facing up, firm soil around and over bulbs, and water.

General Care

If healthy plants and beautiful blooms are desired, continuing care must be given. Weeds can be controlled by spreading a 2-inch (5.1 cm) layer of mulch over the bed at planting time. Weeds that do grow through the mulch should be removed before they become firmly established in the bed.

General care includes fertilization once or twice during the growing season with a special bulb fertilizer or 1 or 1 1/2 lbs of 12-4-8 or an equivalent amount of other complete fertilizers per hundred square feet (10 m²) of bed. Bulbs such as tulips and hyacinths that are usually discarded after flowering need not be fertilized since they have enough stored food to last through the blooming period.

Water relations are a crucial phase of bulb growing, and it is important that plantings do not suffer for lack of water during times of growth and flowering. Except when bulbs are being dried off at the end of a growing period, keep the soil moderately moist at all times. Frequency of watering will depend greatly on soil type, time of year and weather conditions.

A good cultural practice is to remove dead blooms before seeds are produced. Flowering in the following season will be reduced considerably if seeds are allowed to set. Removing dead blooms also helps to maintain the aesthetic value of the planting and may prevent disease problems.

Many bulbous plants grow best if left in the ground year after year while others may become crowded and bloom poorly. Digging and replanting usually encourages more uniform flowering and larger flowers. It may be desirable to dig certain bulbs annually so that they can be replaced with other plants in the bed. Tropical bulbous plants, such as caladiums growing in north Florida, should be dug and stored to prevent injury by cold winter temperatures.

After digging, bulbs should not be exposed to the sun, but should be left in a dry, well-ventilated place for a few days. The roots, dead leaves, and soil are then removed and the clean bulbs are placed in single layers in trays and stored. To reduce the chance of insect and disease damage, a combination of fungicide and insecticide dust may be applied.

Special techniques in planting and general care peculiar to certain bulbous plants will be mentioned in the cultural notes section of Table 1 and Table 2 .

Propagation

Enlarged storage organs of bulbous plants are often used in vegetative propagation. True bulbs (amaryllis, hyacinth, narcissus) develop miniature bulbs, known as bulblets, which, when grown to full size, are known as offsets. Offsets can be separated from the mother bulb and replanted into beds. The number of growing seasons required for the offsets to reach flowering size will depend on the kind of bulb and size of the offset. Some bulbs such as amaryllis, blood lily, hurricane lily and spider lily can be cut into several vertical sections and each section planted upright in a mixture of equal volumes of sand and peat. Bulblets will develop from the basal plate between the bulb scales. These can then be transplanted into beds to continue development. Lily bulbs can be increased by removing individual scales and planting them about 1 to 2 inches deep in moist peat and sand. Within 3 to 6 weeks, 3 to 5 bulblets will usually develop from each scale.

Corms, such as gladiolus and watsonia, produce new corms on top of the old corms, which wither. Miniature corms called cormels are produced between the old and new corms. These can be separated from the mother corms and stored along with the new corms over winter for planting in the spring. New corms usually produce flowers the first season, but cormels require 2 or 3 years of growth to reach flowering size.

Tubers (caladium, gloriosa), tuberous roots (dahlia, ranunculus) and rhizomes (canna, day lily) are propagated by cutting them into sections, each containing at least one bud. Special care should be taken when dividing dahlia tuberous roots to ensure that each tuberous root has a piece of crown bearing a healthy bud. Tuberous roots that are broken off without a bud are worthless.

Many bulbous plants produce seed that will germinate and grow into flowering plants. This method of propagation is not very popular because many varieties today are hybrids, so flower color and type may be highly variable and results can't be predicted.

Diseases and Pests

Bulbous plants are susceptible to damage by many diseases and pests. The most difficult diseases to control are insect-transmitted viruses. Symptoms of virus infection are stunted growth, mottled or striped leaves, and malformed foliage and flowers. The only treatment for virus is to destroy infected plants and to control insect vectors.

When the soil remains extremely wet because of poor drainage, soilborne bacteria and fungi may cause some bulbs to rot. Once the pathogen has invaded the root zone, little can be done to control the disease. Improved soil drainage and removal of infected plants will help to control this problem. Spraying with a bactericide or fungicide may be helpful if the damage is not too severe.

Chlorosis or yellowing of bulb foliage is a common symptom caused by lack of nitrogen, iron, zinc, magnesium or manganese. This may be caused by an actual deficiency of these elements in the soil, or roots may be unable to absorb these nutrients due to poor aeration, disease, or nematodes. The availability of iron and manganese is also limited in high pH soils. All of these factors may interact, making it difficult to determine a specific cause for chlorotic foliage. Publications on adjusting soil pH and correcting nutritional disorders can be obtained from your local county extension office.

Insects directly damage bulb plants and allow disease organisms into plant tissue. Chewing insects such as caterpillars and grasshoppers should be carefully monitored and controlled by hand picking. Pesticides should only be used when the infestation can't be controlled manually.

Aphids are soft-bodied, sucking insects varying in size from 1/25 to 1/8 inch (1 to 3 mm) in length. Aphids suck plant fluids and cause new growth to curl and become distorted. The most serious result of aphid infestation, however, may be the spread of virus diseases. Complete control is essential for bulbous plants such as tulip, calla lily, dahlia, gladiolus, hyacinth and iris, which are adversely affected by virus diseases.

Thrips are tiny insects (1/25 to 1/12 inch [1 to 2 mm] in length) that feed by rasping soft plant tissue and sucking plant fluids. They commonly invade flowers during the warm, dry season of springtime causing brown spots on petals and preventing buds from opening. Complete control is difficult as reinfestation from neighboring plants is the general rule.

Spider mites are tiny animals (1/50 inch [0.5 mm] long) that cause injury similar to that of sucking insects as they feed on the leaves of bulbous plants during warm, dry periods. Bulb mites attack rotting bulbs and tunnel into healthy bulbs, transmitting organisms that produce bulb rot. Bulb mites are particularly damaging to bulbs of amaryllis, gladiolus, hyacinth, lilies, daffodil and tulip.

Mealybugs are soft-bodied insects covered with a white, waxy material. When mature, they vary from 1/50 to 1/3 inch (0.5 to 8.5 mm) in length. They damage plant foliage by sucking plant fluids and may invade stored bulbs. Some control can be obtained by frequent syringing with a hose.

Many bulbous plants are damaged by microscopic, transparent, wormlike animals called nematodes. Best known to gardeners are the root-knot nematodes that make galls on roots. Nematodes feed on the roots and may cause disintegration of the basal plate of some bulbs when present in sufficient numbers. When an infestation builds up in the soil, replant bulbs in another area or treat the area with a soil sterilant.

When pest infestations are severe or where large numbers of plants are involved, chemical control may be needed. For recommendations on selection and application of insecticides, miticides and soil sterilants, contact the agricultural extension agent in your county.

Animals such as moles, pocket gophers, rabbits and squirrels can damage bulbs and bulb-like structures. Trapping is probably the most effective control for these pests. Repellents may keep rabbits away when used as directed.

Bulbs in South Florida

The informality of most south Florida gardens means that bulbs are normally used in small groups among shrubs or herbaceous ground covers rather than in beds by themselves. This makes it difficult to treat the soil against nematodes and means that the most popular and successful bulbs are those that thrive under the same cultural treatment as the rest of the plants in the bed.

Most of the bulbs familiar to northern gardeners are not satisfactory in south Florida. Even when bulbs are brought in from cool regions and given the necessary cold treatment to induce blooming, the flowers will be very short-lived and often smaller and less brightly colored than usual.

In Table 1 and Table 2 , the column headed Zone has two entries for south Florida to distinguish between those bulbous plants that are well adapted and those that need special care. The entry S means that the plants can usually be used in mixed beds with good success. Those marked (S) are not robust enough to do well in ordinary garden situations. Those without either of these symbols cannot be recommended. Further information is given in the cultural notes column where applicable. The planting season in south Florida is usually longer than that stated. The plants can be moved any time except when they are in bloom.

Table 1. Bulbs for Florida

• Key for "Zone" column: Zone = section of state which adapted; NCS = Entire state; N = North Florida, Pensacola to Jacksonville and south to Ocala; C = Central Florida, Leesburg south to Punta Gorda and Ft. Pierce; S = South Florida, Stuart to Fort Myers and south to Homestead; (S) = Denotes plants that will not do well in typical south Florida gardens

Table 2. Bulbs for the Avid Gardener

• Key for "Zone" column: Zone = section of state which adapted; NCS = Entire state; N = North Florida, Pensacola to Jacksonville and south to Ocala; C = Central Florida, Leesburg south to Punta Gorda and Ft. Pierce; S = South Florida, Stuart to Fort Myers and south to Homestead; (S) = Denotes plants that will not do well in typical south Florida gardens

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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