Toronto Master Gardener Factsheet    

Light

• Ferns generally grow best in filtered or diffused light i.e. a bright position out of the direct rays of the sun or near a window filtered by a sheer curtain.
• Ferns will not tolerate a strong summer sun but some will accept an east or west window in summer.
• In winter a full southern exposure is beneficial for some ferns since the sunlight is usually of shorter duration and weaker intensity.
• Northern windows, except perhaps a bright unobstructed one in summer, are not bright enough for most ferns.
• Ferns receiving too much light are less luxuriant, lose their colour and may develop brown leaf margins.
• Ferns receiving too little light may fail to grow or may produce tall, spindly, undersized fronds.

Temperature

• Ferns vary considerably in their temperature requirements as these usually depend on the native environment of the species: they grow not only in the tropics but also near the Arctic and Antarctic.
• Ferns sold as houseplants have been grown in greenhouses and will do best in a temperature range of 19 -27 degrees C with a 5 degree C drop at night.
• Ferns are reasonably adaptable to slight variations in temperature but a uniform day-night cycle is best.
• Excessive heat or drafts, especially around windows in winter, are fatal.
• Air temperature is warmer close to the ceiling so hanging plants must be watered more frequently than table or floor plants.

Humidity

As a rule ferns do not thrive in low humidity. To increase the humidity you can:

• Mist twice a day with tepid water
• Group plants
• Set pots on pebbles in a tray with water. Be sure the pots are on the pebbles above the water line.
• Place in a room that generally has higher humidity
• Supply a humidifier

Watering

• Most ferns prefer to be moist but not wet.
• Roots need oxygen for life and growth. If plants are overwatered the oxygen is pressed out and the soil packs down so that roots eventually die from rot.
• Signs of overwatering: the soil is still wet 3 or 4 days after watering; the soil feels soggy and smells sour; the pot is unusually heavy for its size.
• Some will tolerate an occasional drying out without collapse of foliage.
• Properly moist soil should look and feel damp. If the soil is dry 1.5 - 2.5 cm down from the top, it is time to water again.
• Be sure that the whole root ball is moistened and excess water seeps out the drainage hole.

Fertilizing

• Ferns generally need little fertilization in humus-rich soil to maintain normal growth when grown outside
• A single application every 4 - 6 months is sufficient.in the garden or indoors between October and March.
• During the active growth period - usually spring and summer - more frequent applications may be required.
• Indoors apply fertilizer once a month between April and September. A 20:20:20 or kelp or fish emulsion fertilizer is recommended.
• Resting or inactive plants do not need fertilizer.

Soil and potting

• To perform best, ferns need a soil suited to their needs. Generally speaking, packaged soils, although a good base for your fern mix, do not contain sufficient humus or sand or perlite for adequate drainage.
• To ensure healthy plants, add some or all of the following materials to your soil mix:
1. Humus - usually sphagnum peatmoss - chopped or milled. To pretreat it to hold moisture, pour boiling water over the peat, let it soak, wring out the excess water after it has cooled.
2. Charcoal - this absorbs toxic gases and salts caused by poor aeration in water-logged soils. Be sure to purchase a horticultural grade of charcoal. Place a layer at the bottom of the pot; also add it to the general soil mix.
3. Perlite - white, sterile, volcanic rock, lightens the soil, improves drainage and aeration. Use medium or coarse grades - sharp sand can be substituted for perlite.
4. Sand - improves drainage and aeration of soil. Use sharp sand or builder's sand not fine sand.
5. Lime - horticultural limestone for an alkaline soil which ferns prefer.
6. Bonemeal - a phosphorus-rich fertilizer to add to the soil at the time of potting or repotting - 1ž2 teaspoon under the roots.
• Basic soil mix: 1 part packaged general houseplant soil

1 part humus
1 part sharp sand or perlite

Further reading

• Fern Growers Manual, Barbara Joe Moshizaki
• Ferns and Fern-allies of the U.S. and Canada, David B. Leilinger
• Ferns of Grey and Bruce, Bruce Grey Plant Committee

 

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: This factsheet was created prior to May 2005.