GREENHOUSE PRODUCTION OF BOSTON FERNS

The Boston fern is actually a cultivar of a wild fern found in Florida called the Sword Fern (Nephrolepis exaltata). The Boston fern easily gives 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. New cultivars appear on the market periodically and many have been lost due to changes in consumer demand.

Boston fern is mostly propagated from tissue culture, although stolons or runners harvested from stock plants are still utilized. From either method, plantlets or liners are established in plug trays and marketed to growers who transplant and finish the plants. Most small to medium sized fern growers purchase plug flats from specialized propagators.

The majority of Boston ferns are grown in 8-, 10-, or 12- inch hanging baskets, but 4- to 8-inch pots are also used. Most plastic hanging baskets come with either an internal reservoir or an external, detachable saucer. Many growers prefer to remove saucers at the time of potting to avoid waterlogged media when plants are small. Saucers are then re-attached prior to sale. Generally, the 10- or 12-inch baskets are more desirable than smaller sizes because they hold a larger volume of medium and dry out less frequently.

The potting medium for Boston ferns should be well aerated and drained, but have a high water-holding capacity. Many soilless 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% coarse peat and add a drainage material such as perlite (horticultural coarse grade) and/or vermiculite (No. 3, coarse grade). Aged pine bark (1/16-to/2-inch particle sizes) may also be used for up to 15% to 20% of the mix. Higher % of pine bark increase fertilizer requirements. Amendments should include dolomitic limestone to raise the pH to 5.0 to 5.5. Start with about 5 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 manufacturer directions for micronutrient rates.

Production schemes: 1) transplant to immediate containers such as 4- or 5-inch pots. Once the pots fill out, transplant to hanging baskets. 2) transplant liners directly to hanging baskets and hang baskets in their final location immediately after potting. 3) place newly planted baskets on benches, pot-to-pot, for a period of 2-6 weeks to get liners established and then hang the baskets in the final growing locations.

Boston ferns grow most rapidly if maintained evenly moist, but not saturated for a long period. Supply frequent irrigation during warm, bright, summer conditions, especially for mature plants. If allowed to get too dry, the foliage develops a gray cast and growth and runner production slows. Avoid watering on dark, overcast days unless the medium is clearly dry, but be prepared to water when the sun comes out.

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 fertilizer 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. Try alternating fertilizer and clear water. Many growers supplement the liquid fertilizer program by top- dressing with a slow release fertilizer (Osmocote or Nutricote). Use the ! lower CLF rate indicated above. Slow release fertilizer may also be incorporated at the time of soil mixing. However, uniform mixing with the medium can be a problem.

The best quality Boston ferns are produced at 2500 and 3500 foot-candles. The higher intensity can be used during the late fall, winter, and early spring when temperatures are controllable and 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% - 60% shade fabric or a liquid shading compound to the glazing. Light intensity that is too low results in long, weak, pendulous fronds that are dark green in color, but few in number. Too much light causes fronds to be light green in color.

Generally, Boston ferns grow well with a night temperature (NT) of 65 F and a warmer day temperature (DT) that does not exceed 95 F. Night temperatures of 68 F may be used to speed development of young plants, while a temperature of 62 F can be used to hold mature plants. Recent research has shown that maximum frond length, frond unfolding rate, and shoot dry weight was achieved with an average daily temperature of 77 F (DT+NT/2). Be aware that greenhouse temperatures may stratify vertically with warmer temperatures occurring up high where hanging baskets are located. Temperatures at hanging basket level may be 10 or more degree warmer than at bench level.

The most common diseases are: 1) Pythium or Phytophthora: wilting, and graying or yellowing of the foliage. Stunted brown roots, and outer portions of the root slide away from the inner core. They are more likely to occur in cool, dark weather and cool, wet media. 2) Rhizoctonia: Aerial blight that occurs mostly in the summer. Symptoms include brown irregular lesions commonly in the crown or inner canopy of the plant. The lesions can spread rapidly and cover the entire plant. Check plants frequently in the summer and take corrective measures immediately if found.