Tropical Plants Offer New Possibilities for Georgia Gardens

Bulletin 1272

Bodie Pennisi¹
Paul Thomas¹
Allan Armitage²

Overview
Challenges and Opportunities
Savannah Trial Garden
Griffin Trial Garden
Tropical Plants in Annual Beds
Landscape Considerations for Tropical Plants
Production Consideration
Selling Foliage for Landscape
Marketing Strategies
Summary
Tables

Overview

Figure 1. Tropical plants in the landscape can create an exotic garden, an impression of an island paradise. or a tamed jungle with all of its magic and mystery.

Consumers and avid home gardeners have become more adventurous with their plant choices, and are prompting other growers and landscapers to become more savvy in catering to this spirit of landscape adventure. Anything that adds interest to the landscape design and makes it unique can evolve into a trend - incorporating more non-traditional plants, for example, such as exotic and tropical annuals and perennials. But Flowers are taking a step back, leaving the landscapers to focus on the foliage instead, and to explore variations in texture and color.

Challenges and Opportunities for the Ornamental Industry in Georgia

Georgia climate zones with average minimum temperature ranges and examples of cities in those areas. Zone 7a has a minimum temperature of 0 to 5 degrees F and contains Blairsville. Zone 7b has a minimum temperature of 5 to 10 degrees F and contains Griffin. Zone 8b has a minimum temperature of 10 to 15 degrees F and contains Tifton. Zone 8b has a minimum temperature of 15 to 20 degrees F and contains Savannah.

Figure 2. Georgia climate zones with average minimum temperature ranges and examples of cities in those areas, adapted from USDA hardiness map (www.usda.gov).

The seemingly insatiable consumer demand for new plants presents a challenge and an opportunity for the Georgia ornamental industry. Georgia has a diverse climate (Fig. 2), from zone 8b in the South and coastal areas, where minimum average temperatures range from 15-20 degrees Fahrenheit, to zone 7a in the northern mountain region, where minimum average temperatures range from 0-5 degrees Fahrenheit. A small part of North Georgia is in Zone 6b where minimum average temperatures range from -5 to 0 degrees Fahrenheit. The largest area in the state is divided almost equally between zones 8a (minimum average temperatures range from 10-15 degrees F) and 7b (minimum average temperatures range from 5-10 degrees F).

Each of these areas is characterized by unique climate, which presents both a challenge and an opportunity for industry and consumers. On one hand, recommending plants that would do well in all areas is difficult; on another, plants that grow well in one area but not in another provide an excellent opportunity for local use. This is especially true for tender plants that may thrive in the warm weather and may even come back the next season in one area, but not in other areas. Such plants may receive enormous recognition seven to eight months of the year, but because they are not truly perennial (able to survive the cold weather and grow back the next season), they may not get recommended and/or marketed by the industry. Some of these plants, termed tender perennials, tropicals, etc. , may receive much attention in northern areas in Florida, for example, while few growers and garden centers in South Georgia market them - although both are in the same climate zone. Thus the consumer in Georgia may be largely unaware of the benefits of these tender perennials.

In addition, many plants from the tropics hold up very well in Georgia's challenging spring and summer months, and can tolerate extremes of heat, humidity, and moisture. Some are so uniquely adapted to low-light environments that they can be used in deep-shade areas in a garden. Shade gardening, however, has challenged landscapers because of a limited selection of species, which do well in low light environments. Few flowering plants perform well in such areas, especially where light levels dip below 1000 ft-c; for example, under oak shade, light levels frequently average around 500 ft-c. Tropical plants adapted to deep shade are uniquely suited to thrive in low-light habitats with high humidity. Many of them, because of their epiphytic origins, are capable of using small amounts of dew moisture, which accumulates in the early morning hours during summer, either by direct absorption through the foliage or by channeling moisture into their leaf whorl.

Two photos of garden areas consisting of tropical leafy plants in varying colors.

Figure 3. Colorful combination gardens created exclusively with tropical foliage plants. The combination container on the left features high-light adapted plants and can be used on patios, sun decks, around pools, etc. The container on the right uses plants best adapted for low-light environments. During the cold months, a combination garden can be brought inside the house and treated as an indoor planting. This further illustrates the versatility of tropical plants.

Tropical plants may also be used in annual beds in combination with traditional flowering plants. The bold vegetative look of foliage plants can add height and texture, while achieving a tropical look that is attractive and highly sought after. Yet the use of tropical plants may not be limited to landscape. Combination gardens in various-sized containers have become very popular with consumers. Visually appealing and colorful combinations using tropical plants alone or in combination with other flowering plants can be created (Fig. 3). Such gardens hold high appeal for gardeners in urban areas because of the limited garden space.

Finally, numerous new tropical species and cultivars - many with bold, multicolored foliage, and quite a few flowering varieties - have come to market in recent years. Some new introductions show improved cold tolerance and have been used successfully in landscapes throughout southern states, especially in Florida.

Further exploration of the landscape potential of new ornamental species and cultivars is needed and could provide recommendations and guidelines to the industry and consumers. The goals of these investigations were to achieve an aesthetically pleasing landscape while experimenting with mixing various plant habits, leaf textures and colors, and even flowers, and to raise consumer awareness, both at industry and public levels, of the alternative uses of tropical plants in the landscape.

This publication presents plant performance data collected over a three-year period in trials from two different Georgia environments, a coastal area and a mid-state area.

Trial Gardens Locations, Conditions, and Plant Performance

Tropical Plant Trial Garden at the Bamboo Farm and Coastal Gardens in Savannah, Georgia (evaluation period April 2002 - October 2004)

Figure 4. Full shade bed at the Bamboo Farm and Coastal Gardens in Savannah, GA.

Climate conditions: USDA Hardiness Zone 8b, Minimum Temperature Average Range 15 to 20 F.

Species planted: bromeliads, ficus, philodendron, schefflera, spathiphyllum, ferns, alocasia, colocasia, ornamental banana, gingers (alpinia, calathea, kaempferia, cornukaempferia, curcuma, globba, siphonochilus, costus).

Light conditions: full shade (light levels 500 to 1100 ft-c) (Fig. 4).

Raised beds (soil depth of 8-10 inches) amended with 0.1 pounds of nitrogen per 100 sq.ft. at planting and once in mid summer.
Plant size at planting: 6" containers, colocasia, 3-gal containers.
Plant spacing: 12" x 12" for the 6" container size, 24" x 24" for 3-gal containers.

Irrigation: for the first 4 weeks after planting, plants were watered twice per week and for the remainder of the season received 38 inches of natural irrigation (from April to December, 2002).

Plant Performance and Hardiness

Throughout the growing period April - December 2002, all species planted in the garden did very well with some species growing as much as one and a half times in size, creating a beautiful shade landscape.

Although most alocasias and colocasias grow best in high light, they grew well in the shade garden, while retaining a more compact growth (Table 2). This may be a desirable trait for small-sized gardens. We noted that the strong-colored colocasia foliage lost the intensity of its deep purple coloration.

Gingers (Peacock and Hidden Gingers) showed excellent performance and strong landscape impact (Table 2). Some of the best performers were Cornukaempferia 'Jungle Gold', Kaempferia 'Grande', Curcuma 'Emperor', Globba 'White Dragon', and Calathea tigrinum. With the exception of C. tigrinum and Siphocilius decora , all other gingers produced flowers throughout the season (Fig. 8).

Ficus, philodendron, schefflera, bromeliads and spathiphyllum showed excellent performance and strong landscape impact (Table 2).

No major pest or disease problems were encountered during the season of active growth and no pesticides were applied. No herbivory by deer was noted.

Planting Recommendations

High visual impact combinations were achieved by using:

Low to medium plants: philodendrons ('Black Cardinal', 'Prince of Orange'), bromeliads (Guzmania minor magnifica , Neoregelia 'Grace', and Aechmea fasciata 'Morgana'), Spathiphyllum 'Petite', Homalomena 'Purple Sword', Kaempferia 'Alva', Kaempferia 'Grande', Schefflera arboricola 'Luseanne', Cornukaempferia 'Jungle Gold', and ferns (Selaginella involvens 'Aurea', Arachniodes simplicior, Onoclea sensibilis);
Medium to tall plants: Ficus benjamina 'Midnight', Schefflera 'Nova', Calathea tigrinum, Calathea 'Ice Blue', Calathea 'Silver Plate', Carludovica 'Jungle Drums', Alocasia odora, Alocasia wentii, Alocasia gagaena, Globba 'White Dragon', Curcuma 'Emperor', Siphonochilus decora, Costus amazonicus, Alpinia zerumbet variegata, Philodendron pinnatifudim;
Tallest plants: Alocasia macrorrhiza, Colocasia esculenta nancyana, Colocasia illustris, Colocasia esculenta 'Black Magic' and Musa zebrina; should be planted toward the back of the border or in a center of an isle bed.

Plant Hardiness

Underside of Alocasias and Colocasias leaf.

Globba 'White Dragon' plant with flowers

Figure 5. Regeneration and growth of plants in the Savannah Trial garden. A) Alocasias and Colocasias; B) Calathea tigrinum; C) Globba 'White Dragon'; D) Siphonocilius decora; E) Ficus benjamina 'Midnight'; F) Spathiphyllum 'Petite'; and G) Calathea 'Ice Blue'.

The two winter periods of 2002-2004 provided opportunities to test plant hardiness. We had numerous occurrences when night temperatures were between 19 to 25 degrees F.

Percent survival and growth in the second and third year for species and cultivars that survived the winters are listed in Table 1 and illustrated in Figure 5. Remaining species not listed in the table were not root-hardy and did not survive the first winter.

Tropical Plant Trial Garden at the Research and Education Gardens, Griffin, Georgia (evaluation period May-December 2004)

Figure 6. Trial areas at the Research and Education Gardens, Griffin, Georgia. A) Full sun; B) Part sun (morning shade, midday sun, afternoon shade); C) Part shade (no direct sun); and D) Full shade.

Climate conditions: USDA Hardiness Zone 7b Minimum Temperature Average Range 5 to 10 - F.

Species planted: alocasia, colocasia, gingers (calathea, kaempferia, cornukaempferia, curcuma, begonia). For a complete list of species and cultivars refer to Table 2 and Table 3.

Light conditions:

full sun (Fig. 6A)
part sun (morning shade, midday sun, afternoon shade) (Fig. 6B)
part shade (no direct sun) (Fig. 6C)
full shade (light levels 800 to 1100 ft-c) (Fig. 6D)

Raised beds (soil depth of 8-10 inches) amended with 0.1 pounds of nitrogen per 100 sq.ft. at planting and once in mid-summer.

Plant Size at planting: 6" containers, alocasia and colocasia, 1-gal containers.

Plant spacing: 12" x 12" for the 6" container size; 18" x 18" for 1-gal containers.

Irrigation: for the first 4 weeks after planting plants were watered twice per week and for the reminder of the season (May to November) received 35 inches of natural irrigation.