Boston Fern Production Guide

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CFREC-A Foliage Plant Research Note RH-91-8

R.W. Henley, L.S. Osborne and A.R. Chase University of Florida, IFAS Central Florida Research and Education Center - Apopka 2807 Binion Road, Apopka, FL 32703-8504


BOSTON FERN

The commercial foliage plant industry of central Florida began in 1914 with Boston fern (Nephrolepis exaltata `Bostoniensis') and related sword ferns. There are approximately 30 tropical species of Nephrolepis, many of which are cultivated as potted plants or landscape plants (4). Of these species, Nephrolepis exaltata is the most widely grown in the United States. Although the term - Boston ferns - has been used as a collective name for all the cultivars of N. exaltata in this publication, most fern authorities prefer to call them sword ferns.


CULTIVARS

It is difficult to know how many cultivars of Nephrolepis exaltata exist, because new forms occur periodically and others are lost from cultivation, often due to fluctuating consumer demand for certain cultivars. Although over 50 cultivars are listed in Hortus III (1), most of them are not presently recognized as "commercial" varieties. Some of the N. exaltata cultivars grown in Florida are described below:

`Bostoniensis' is one of the early selections made from plants shipped from Florida. It is a very large fern which is more pendulous and graceful than the native strains of sword ferns which have a bristly habit of growth.

`Bostoniensis Compacta' has been for many years and continues to be one of the most popular cultivars. Its fronds are shorter, more compressed and less pendulous than `Bostoniensis'. Bostoniensis Compacta' is an intermediate size fern.

`Dallas' is a relatively new, small cultivar which is now being grown by a large number of nurserymen because of the plant's popularity. `Dallas', also sold under the trademark `Dallas Jewel', is patented (plant patent number 5755). The fronds of this cultivar are once divided, bearing short, broad pinnae (leaflets) on a short rachis (midrib of the frond). The growth habit and relatively less leaf surface area of this cultivar provides for better air drainage and light penetration to the crown than observed in most cultivars, which appears to help it survive indoors. Although `Dallas' has rather short fronds, the crown of the plant spreads rapidly, making it popular with the growers.

`Florida Ruffle' is an intermediate size fern with rather stiff fronds which are twice divided and very broad at the base. The width at the base of the frond is usually one third or more of the length, and tapers toward the tip. The broad base of these fronds create a very dense canopy over the crown that frequently leads to maintenance problems during production and when the plants are placed indoors.

`Fluffy Duffy' is a small fine-textured plant with fronds two to three times divided and extensively overlapped. Frond width at the base exceeds one half its length. The overlapping structure of each frond provides the plant with a unique, three-dimensional, sculptural quality. Due to the extremely dense canopy of this variety, it is quite prone to infection with Rhizoctonia during production. Keeping quality indoors is also limited.

`Massii' resembles `Bostoniensis', except it more pendulous and darker green.

Other cultivars of N. exaltata which are occasionally grown in Florida, but not described, include: `Fluffy Ruffles', `Hillsii', `Petticoat', `Plymouth Ruffles', `Rooseveltii', `Welchii' and `Whitmanii'(3).

Other species and cultivars of Nephrolepis which are occasionally grown in Florida, but not described, include: N. biserrata `Furcans' and N. cordata `Duffii'(3).

Reference to University of Florida/IFAS Pest Control Guides


PRODUCTION

Boston ferns are usually sold as hanging baskets or potted plants in a variety of container sizes, depending upon market demand and the growth habit of each cultivar. Some of the most popular container sizes for the cultivars described previously are displayed in Table 1.


Table 1. Popular container sizes for six cultivars of Nephrolepis exaltata.

Cultivar             4-inch  6-inch  8-inch  10-inch  12-inch  Over 12-inch

Bostoniensis           no      no      yes      yes      yes       yes

Bostoniensis
Compacta               no      yes     yes      yes       no        no

Dallas                yes      yes     yes       no       no        no

Florida Ruffle        yes      yes     yes       no       no        no

Fluffy Duffy          yes      yes      no       no       no        no

Massii                 no       no     yes       yes      yes       yes
 

Historically, Boston ferns have been grown from offsets harvested from stolons (runners) of older plants. Most of the early nurserymen of central Florida grew their stock plants in ground beds inside cypress lath-covered shadehouses. As the offsets matured they were pulled from the beds, wrapped bare-root in newspaper and shipped to northern markets where many retail customers would purchase them in that form. Others were shipped to growers who would pot and finish the plants for local sales.

Today most Boston type ferns grown in central Florida are finished potted plants or hanging baskets produced in greenhouses which provide maximum environment control. Stock plants are still frequently maintained in stock beds or in raised benches. Today growers either start with plantlets pulled from stock plants or use liners started in plug trays or small pots. In recent years tissue culture has become a common means of propagating a few cultivars. Variation of cultivar characteristics from tissue-cultured plants of some cultivars and relative ease of finishing plantlets collected from stock plants suppresses the tissue culture option.

Boston ferns have a wide tolerance to changing light levels, but grow well when receiving 1500 to 3000 ft-c, with best quality usually produced near 2000 ft-c. Because of the wide spreading habit of these ferns, growers frequently start hanging baskets pot-to-pot and then hang them at the final spacing for finishing. Suggested fertilizer level is 2.9 pounds of actual nitrogen per 1000 square foot per month from a 3-1-2 or 2-1-2 ratio fertilizer. Most growers prefer the liquid option because it can be manipulated more effectively than the slow-release materials.

Potting media utilized for Boston fern should have high water-holding capacity, good aeration and not dry rapidly. Amendments should include a low to moderate level of micronutrients such as 1 lb MicroMax/yd3 and sufficient dolomite to adjust medium pH to 5.0 to 5.5. Higher pH levels have been shown to slightly reduce growth rate. Suggested air temperature for best growth is 65F minimum and 95F maximum; however, Boston ferns will tolerate slightly lower and higher temperatures without great change in growth habits. Boston fern are fairly tolerant to ethylene.


PHYSIOLOGICAL PROBLEMS

1) Graying

Symptoms - Fern has gray cast with reduced growth rate and few runners.

Control - Boston fern will turn gray if it does not receive sufficient water, and growth rate and runner production will be decreased if potting medium is not moist all the time. Increase irrigation to supply sufficient water.

2) Weak fronds

Symptoms - Plants have a reduced number of fronds that are long, weak and pendulous. Fronds are usually dark green in color and overall plant quality is poor.

Control - Increase light level to reduce frond length and increase strength. Too much light will cause fronds to become light green in color.

3) Leaf tip and Runner burn

Symptoms - Frond tips and leaflets and runner tips turn brown and die.

Control - High soluble salts have been associated with tipburn and leaching of media with good quality irrigation water will reduce problem. In other cases tipburn has been associated with chemical phytotoxicity from sprays or poor quality irrigation water.

Reference to University of Florida/IFAS Pest Control Guides


FUNGAL PROBLEMS

1) Pythium root rot (Pythium spp.)

Symptoms - Boston fern which are infected with Pythium spp. show a variety of symptoms including stunting, wilting and graying or yellowing of fronds. Examination of the roots shows a stunted, brown root system with little vigor. The outer portion of the roots frequently falls away from the inner core. Gray, water-soaked areas occur on portions of the roots which are not completely rotted. Since ferns with root rot do not always wilt, observation of a gray overcast to the foliage may signal root problems.

Control - A pathogen-free potting medium is the first step to control of pythium root rot and other root pathogens. Plants should be produced from pathogen-free stock and grown in new or sterilized pots on raised benches. Chemical control of pythium root rot can be achieved.

2) Rhizoctonia aerial blight (Rhizoctonia solani)

Symptoms - Rhizoctonia aerial blight occurs primarily during the summer months. Disease development can occur in less than a week, so plants should be checked carefully and frequently. Brown irregularly shaped lesions form anywhere in the foliage, but most commonly within the crown of the plant which is often wet. Sometimes the first lesions form near the top of plant confusing the source of the disease (the soil). The lesions spread rapidly and cover the entire plant with the brown weblike mycelium of the pathogen.

Control - Cultural control of this disease is the same as that discussed for pythium root rot. Since this pathogen inhabits the soil both the roots and the foliage of the plants must be treated to provide optimal disease control.

Reference to University of Florida/IFAS Pest Control Guides


NEMATODE PROBLEM

1) Lesion nematode (Pratylenchus spp.)

Symptoms - Nematode infested plants appear similar to plants with fungal root rot disease. Graying of foliage, a sign of water stress, is common.

Control - Cultural control of lesion nematodes is the same as that discussed for Pythium root rot.

Reference to University of Florida/IFAS Pest Control Guides


INSECT AND RELATED PROBLEMS

The major arthropod pests of Boston fern include caterpillars, mealybugs, false spider mites, scales and thrips. Mealybug and scale infestations are typically the result of bringing infested plant material into the greenhouse. Moths (adult stage of caterpillars) and thrips have the ability to fly and thus invade the greenhouse from weeds and other infested plants outside. In the control section a few of the many registered and effective pesticides will be listed. For a complete listing please consult the references at the end of this report.

1) Caterpillars (worms)

Symptoms - Infestations are easy to detect because worms, their excrement and the damage they cause, are usually quite visible to the unaided eye. Damage appears as holes in the center or along the edges of leaves. Damage by worms is often confused with slug or snail damage. The only way to determine which pest is involved is to find a specimen. Old damage can be distinguished from new by the calloused appearance of the older damaged areas (worms are usually gone by this time).

Control - Reference to University of Florida/IFAS Pest Control Guides

2) Fungus gnats

Symptoms - Fungus gnats are small black flies (1/8 inch long) and are frequently observed running around the soil surface or on leaves and are often confused for Shore flies (see later section). The adults have long bead-like antennae and their legs hang down as they fly. These insects are very weak fliers and appear to "flit" around randomly. The larvae are small legless "worms" with black heads and clear bodies that inhabit the soil. The larvae spin webs on the soil surface which resemble spider webs. Damage is only important on small tissue cultured and is caused by larvae feeding on roots, root hairs, leaves in contact with the soil and lower stem tissues. Feeding damage may predispose plants to disease and they are often found in close association with diseased plants or cuttings. Adults do not cause any direct damage, but are responsible for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance. For further information please consult Extension Entomology Report #74 (Management of fungus gnats in greenhouse ornamentals).

Control - Reduce the amount of water applied to each pot where possible. Avoid algae growth where possible. Soil drenches or soil-surface sprays are effective at controlling the larvae. Nematodes that seek out insects in the soil are sold commercially and have been shown to control these pests without causing any negative effects to the host plants. Adults are very sensitive to most chemicals.

3) Mealybugs

Symptoms - Mealybugs appear as white, cottony masses in leaf axils, on the lower surfaces of leaves and on the roots. Honeydew and sooty mold are often present and infested plants become stunted, and with severe infestations, plant parts begin to die.

Control - Systemic materials are preferred. Control of root mealybugs is accomplished with soil drenches with an insecticide. When pesticides are applied to the soil, care must be taken to assure that the pots have good drainage and that no saucers are attached, or phytotoxicity may result.

4) Mites (False spider mites)

Symptoms - Mites are very small and go unnoticed until plants become severely damaged. False spider mites (Brevipalpus spp.) are red in color and sedentary. Eggs are bright red and oval-shaped and are laid on both surfaces of leaves. Initial infestations are indicated by faint brown, scruffy flecks, later becoming bronze or reddish in color. Basal leaf areas are affected, vegetative shoot apexes may be killed, and severe leaf drop may occur.

Control - The critical point in any control program is thorough coverage with the pesticide. The best control program is to minimize the possibility of introducing mites into the growing area on infested plant material.

5) Scales

Symptoms - Infested plants become weakened or stunted and begin to die. Scales can be found feeding on leaves, petioles, or stems. They are usually distinct from the plant material on which they are feeding. Their shape (round to oval), size (pinpoint to 2 mm long), and color (light to dark brown) are quite variable and many scales are hard to distinguish from the plant material on which they are feeding.

Control - See Mealybugs

6) Shore flies

Symptoms - Shore flies small black flies (1/8 inch long) and are frequently observed sitting on the tips of leaves or on the soil surface feeding on algae. The adults have very short antennae. These insects are very strong fliers and exhibit directed flight (straight between 2 points). The larvae inhabit the soil and are small legless "worms" with clear bodies and no obvious heads. No known damage is caused by larvae. This insect is believed to feed only on algae. Adults do not cause any direct damage, but may be responsible for spreading plant pathogens, reducing value by defecating on the leaves (small black to green spots) and for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance.

Control - Reduce the amount of water applied to each pot where possible. Avoid algae growth on walkways, benches, and cooling pads. Chemicals are not believed to be very effective in the control of this pest.

7) Thrips (Western Flower Thrips and Banded greenhouse thrips)

Symptoms - Thrips are small (less than 1/20), thin insects. Adult thrips can be identified by a long fringe of hair around the margins of both pairs of wings. Color varies between species with western and other flower thrips being yellow to light brown and banded greenhouse thrips and a few other thrips that feed mainly on leaves being dark brown to black. Feeding takes place with rasping type mouth parts. Infested leaves become curled or distorted, with silver-gray scars or calloused areas where feeding has occurred. Thrips can transmit the tomato spotted wilt virus to many different ornamentals. Any unusual symptoms should be investigated.


Pesticides should be applied according to label directions.

Regardless of the pesticide or mixture of pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all plants.

Mention of a commercial or proprietary product in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.


Reference to University of Florida/IFAS Pest Control Guides


REFERENCES

1. Bailey, L.H. and E.Z. Bailey. 1976.Hortus Third. Macmillan Publishing Co., Inc., New York. 1290 pp.

2. Chase, A.R. 1983. Phytotoxicity of some fungicides used on tropical foliage plants. ARC- Apopka Research Report RH-83-2.

3. Chase, A.R. 1990. Phytotoxicity of bactericides and fungicides on some ornamentals. Nursery Digest 24(5):11.

4. Conover, C.A. and R.T. Poole. 1984. Use of sewage as an irrigation source for foliage plants. AREC-Apopka Research Report RH-84-17.

5. Conover, C.A. and R.T. Poole. 1986. Factors influencing shipping of acclimatized foliage plants. CFREC-Apopka Research Report RH-86-11.

6. Conover, C.A. and R.T. Poole. 1986. Nitrogen source effects on growth and tissue content of selected foliage plants. HortScience 21(4):1008-1009.

7. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. CFREC-Apopka Research Report RH-90-1.

8. Gilliam, C.H., C.E. Evans and R.L. Shumack. 1983. Foliar sampling of Boston fern. J. Amer. Soc. Hort. Sci. 108:(1) 90-93.

9. Henley, R.W. and R.T. Poole. 1975. Propagation of Pteris ensiformis Burm. `Victoriae' by spores. Proc. Fla. State Hort. Soc. 88:407-410.

10. Lang, H.J. and D.W. Reed. 1987. Differential response of foliage plants to iron deficiency. J. of Plant Nutrition 10(8):951-959.

11. McConnell, D.B., R.W. Henley and C.B. Kelly. 1989. Commercial foliage plants: twenty years of change. Proc. Fla. State Hort. Soc. 102:297-303.

12. Mortensen, L.M. 1986. Effect of relative humidity on growth and flowering of some greenhouse plants. Scientia Horticulturae 29:301-307.

13. Mortensen, L.M. and S.O. Grimstad. 1990. The effect of lighting period and photon flux density on growth of six foliage plants. Scientia Horticulturae 41:337-342.

14. Mortensen, L.M. and R. Olsen. 1987. Light acclimatization of some foliage plants. Gartenbauwissenschaft 52(4):157-161.

15. Olson, Wilber W. 1977. The Fern Dictionary, Los Angeles International Fern Society, Los Angeles. 132 pp.

16. Poole, R.T. and C.A. Conover. 1982. Growth of foliage plants at various night temperatures. ARC-Apopka Research Report RH-82-26.

17. Poole, R.T. and C.A. Conover. 1983. Growth comparison of Leatherleaf and Boston fern receiving micronutrients. Commercial Fern Grower 6(12):1-3.

18. Poole, R.T. and C.A. Conover. 1990. Effects of light intensity and fertilizer formulation on six foliage plants growing indoors. CFREC-Apopka Research Report RH-90-16.

19. Poole, R.T., C.A. Conover and A.R. Chase. 1989. Effects of sulfur applications to media containing foliage plants. CFREC-Apopka Research Report RH-89-5.

20. Price, J., D.E. Short and L.S. Osborne. 1989. Management of fungus gnats in greenhouse ornamentals. Extension Entomology Report #74.

21. Rishani, N. and R.P. Rice. 1988. Use of carob as a potting medium component. HortScience 23(2):334-336.

22. Short, D.E., L.S. Osborne and R.W. Henley. 1984. Phytotoxicity of insecticides and miticides to foliage and woody ornamental plants. Extension Entomology Report #57.

23. Short, D.E., L.S. Osborne and R.W. Henley. 1991. 1991-1992 Insect and related arthropod management guide for commercial foliage plants in Florida. Extension Entomology Report #52. 13 pp.

24. Simone, G.W. and A.R. Chase. 1989. Disease pesticides for foliage production (Revision #4) Plant Protection Pointer. Extension Plant Pathology Report #30. [also in Foliage Digest 12(9):1-8]

26. Spinazzola, Lisa (Editor). 1990. Florida Foliage Locator 1990. Florida Foliage Association, 57 East Third Street, Apopka 32703. 172 pp.

27. Woltering, E.J. 1987. Effects of ethylene on ornamental pot plants: a classification. Scientia Horticulturae 31:283-294.