BOSTON FERNS

Commercial Greenhouse Production



Scientific Name: Nephrolepis exaltata 'Bostoniensis'

Common Name: Boston Fern, Sword Fern



Dr. J. Raymond Kessler, Jr.

Auburn University



Introduction

The Boston fern is actually a cultivar of a wild fern found in Florida called the Sword Fern (Nephrolepis exaltata). The sword fern has 3- to 4-foot erect fronds, and was popular as a house plant in the U.S. and Europe in the middle to late nineteenth century. 'Bostoniensis' was discovered by chance in a large shipment of Sword ferns from a Philadelphia grower to a Boston distributor in 1894. Since then, variants have given rise to one of the largest and most popular groups of fern cultivars.

Cultivars

The Boston fern easily give rise to sports or mutations which may or may not be stable. Many of the Boston fern cultivars available today have come about from sports. Though the best cultivars are mostly stable, variations can occur even from vegetatively propagated material. It is impossible to tell how many Boston fern cultivars exist. New ones appear on the market periodically and many have been lost due to changes in consumer demand. The most popular for commercial production today are:

'Bostoniensis' One of the original selections from the sword fern. It is a very large fern with a pendulous, graceful habit.

'Compacta' A very popular, intermediate size fern. It is shorter, more compact and less pendulous than 'Bostoniensis'.

'Dallas' This is a very popular, small size fern which may be sold as 'Dallas Jewel'. The fronds are once divided and the crown spreads rapidly.

'Florida Ruffle' This is an intermediate sized fern with stiff, twice divided fronds which are broader at the base. This creates a dense canopy which can be a problem.

'Fluffy Duffy' This is a small fine-textured fern with fronds two to three times divided with extensive overlapping. This creates a dense canopy which can be a problem.

'Massii' A large fern much like 'Bostoniensis' except it is more pendulous and darker green.

Other cultivars may include: 'Atlanta', 'Blue Bells', 'Erecta', 'Hillsii', 'Petticoat', 'Rooseveltii', 'Welchii' or 'Whitmanii'.

Production

The majority of Boston ferns are grown and marketed in 8-, 10-, or 12-inch hanging baskets, but 4- to 8-inch pots are also popular. The choice of container size is subject to market demand. However, it is important to choose cultivars by final size and growth habit for a particular container size (Table 1). Generally, large cultivars are more appropriate for larger container and smaller cultivars for smaller containers. Cultivars should also be chosen based on ease of production under the cultural conditions available. Some of the denser, finer-textured cultivars may develop disease problems under low-light and humid conditions.



Table 1. Appropriate container sizes for Boston fern cultivars.
Cultivar 4-inch 6-inch 8-inch 10-inch 12-inch > 12-inch
'Bostoniensis' no no yes yes yes yes
'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


Propagation

Boston fern cultivars are mostly propagated from tissue culture, although stolons or runners harvested from stock plants are still utilized. From either method, plantlets are established in plug trays or liners and marketed by specialists propagators to growers that transplant and finish the plants in final containers. The most common tray sizes are 40, 72, 135, or 273 cells per tray. Most small to medium sized fern growers purchase plug flats from specialists propagators to meet production needs.

Potting Medium

The potting medium for Boston fern should be well aerated and well drained, but have a high water-holding capacity so that it will not dry too rapidly. Many commercially prepared mixes sold by suppliers have the characteristics necessary to produce a good crop. This may be the most cost effective alternative for many small growers. However, to mix your own, start with at least 50% course peat and add a drainage material such as perlite and/or vermiculite. Aged pine bark may also be used for up to 15% to 20% of the mix. Higher percentages of pine bark increase fertilizer requirements. Amendments should include sufficient dolomitic limestone to raise the pH to 5.0 to 5.5. Start with about five pounds per cubic yard. A moderate rate of superphosphate (2 pounds per cubic yard) and a commercial micronutrients formulation designed for mixing with medium (Micromax or Esmigram) can also be added. Follow the manufacturers directions for micronutrient rates.

Water

Boston ferns grow most rapidly if maintained evenly moist, but not saturated for a long period. Watering practices should be adjusted for changes in environmental conditions and the age of the plant. Provisions should be made to supply frequent irrigation during warm, bright, summer conditions, especially for mature plants. Hanging baskets and large pots can be watered efficiently using micro-tube irrigation systems. Small pots can be watered using sub-irrigation or by hand using a water breaker. If allowed to get too dry, the foliage of Boston ferns develops a gray cast and growth and runner production slows.

Low light and cool temperature conditions during the winter can be a problem for young, recently potted plants. The grower should watch weather conditions and learn to anticipate watering requirements. Avoid watering on dark, overcast days unless the medium is clearly dry, but be prepared to water when the sun comes out. Try to water early in the morning at a time when the temperature is increasing.

Fertilizer

Liquid fertilization with a fertilizer injector is the most common method of fertilizer application in the production of Boston Ferns. Newly potted plugs should not be fertilized until the roots reach the container margins. Afterward, fertilize with a low ammonium fertilizer such as 15-16-17 peat-lite special, 15-0-15, or a calcium and potassium nitrate tank mix during darker, cooler times of the year. These can be applied at 150 to 175 ppm nitrogen on a constant liquid feed basis (CLF) depending on the stage of growth. One clear watering per week in a CLF program will help prevent soluble salts buildup. During warmer, brighter periods, a 20-10-20 may be used at 175 to 200 ppm nitrogen. Where CLF is not possible, 250-300 ppm nitrogen once per week works well. Rinse the foliage with clear water after applying strong fertilizer to prevent foliar burn. Some sources recommend a fertilizer ratio of 3-1-2 or 2-1-2.

Like watering, the grower should consider the stage of growth and watch weather conditions to learn how to adjust fertilization frequency. CLF works fine when plants are established and during warm, bright weather, but may be too much fertilizer when plants are young or during dark, cool weather. Try alternating fertilizer and clear water.

Many growers supplement the liquid fertilizer program by top-dressing with a slow release fertilizer such as Osmocote or Nutricote at the rate recommended for a particular pot size. Use the lower CLF fertilizer rate indicated above. Slow release fertilizer may also be incorporated at the time of soil mixing at a rate recommended by the product manufacturer. However, uniform mixing with the medium can be a problem.

Media testing and tissue analysis is an important component of maintaining adequate fertility for growing Boston ferns. Testing should be performed every two to four during production by sending samples from each planting to the state soil testing laboratory or a commercial laboratory.



Table 2. Boston Fern Tissue Analysis Ranges
Low OK High
%
N 2.00-2.49 2.50-3.0 >3.0
P 0.15-0.24 0.25-0.7 >0.7
K 1.00-1.59 1.60-3.8 >3.8
Ca 0.50-0.79 0.80-2.5 >2.5
Mg 0.20-0.24 0.25-1.0 >1.0
S 0.15-0.19 0.20-0.5 >0.5
ppm
B 15-19 20-70 >70
Cu 4-5 6-50 >50
Fe 40-49 50-300 >300
Mn 30-39 40-200 >200
Zn 15-19 20-200 >200


Light

The best quality Boston ferns are produced at between 2500 and 3500 foot-candles. The higher intensity can be used during the late fall, winter, and early spring when temperatures are more controllable and the days are short. The lower intensity may be necessary at other times, especially during the summer, to control high temperature. Light intensity reductions in the greenhouse can be achieved by applying a 30% to 60% shade fabric or a liquid shading compound to the greenhouse glazing.

Temperature

Generally, Boston ferns grow well with a night temperature of 65F and a warmer day temperature that does not exceed 95F. Night temperatures of 68F may be used to speed development of young plants, while 62F can be used to hold mature plants. Recent work has shown that maximum frond length, frond unfolding rate, and shoot dry weight was achieved with an average daily temperature of 77F.

Scheduling

Many growers produce Boston ferns for the spring market and production timing depends on the size of the initial plug, the final container size, and the growing conditions. Some growers order established plugs and pot them to 4-inch pots. These will be grown for a time and then transplanted to larger containers such as hanging baskets. Table 3 outlines total production times for transplanting from several common pre-finish containers to several common finish containers.



Table 3. Boston Fern Scheduling
from to 72 cell 40 cell 4" pot 6" pot 8" HB 10" HB
273 cell 6-8 wks 8-10 wks 10-12 wks 16 wks -- --
72 cell -- -- 6-8 wks 10-12 wks 16-20 wks 20-24 wks
40 cell -- -- -- 8-10 wks 14-16 wks 18-22 wks
4" pot -- -- -- 6 wks 12 wks 16 wks
6" pot -- -- -- -- 8 wks 12 wks


Diseases

Pythium or Phytophthora: Symptoms include stunting, wilting, and graying or yellowing of the foliage. More likely to occur in cool, dark weather and cool, wet media.

Rhizoctonia: Aerial blight that occurs mostly in the summer. Symptoms include brown irregular lesions commonly in the crown of the plant.

Insects

The most common are caterpillars, fungus gnats, mealybugs, mites, scale, and thrips.