Naturally grown as epiphytes, staghorn ferns (Platycerium spp.) harmlessly cling to tree branches as they hang downward in the canopy's shade. These bushy evergreens grow slowly, up to 4 feet tall and wide over a period of 10 to 20 years. Although summer is their most active growth and reproductive period, several environmental factors affect their normal growth rate. Staghorn ferns are hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11.
Summer growth is most rapid when your fern is exposed to indirect sunlight, such as under a shady tree or potted indoors near a north-facing window. Radiant sunlight allows the fern to maximize its photosynthesis processes without heat stress or sunscald. Mild temperatures between 70 and 80 degrees Fahrenheit during the day stimulate summer growth. Avoid heavy shade, however, because staghorns react with stunted growth from lack of energy production. Actively photosynthesizing leaves, called foliar fronds, droop downward as basal fronds attach to a substrate, such as a tree trunk. Bright, indirect sunlight encourages summer foliage growth along with ample water trapped among the basal fronds for root absorption.
Roots and Medium
Your staghorn does not grow well during the summer in improper potting medium. In fact, fern roots largely absorb nutrients and moisture from the surrounding air. To pot your fern correctly, use sphagnum peat moss formed into a slight mound. The fern's bud should be pressed into the moss while the basal fronds touch the medium slightly along the sides. Only water the mound when it has dried throughout -- peat moss holds moisture longer than other mediums. You do not want to create a soggy environment in the middle of the container. Healthy roots in a proper medium encourage vigorous summer growth.
Staghorn ferns thrive in high humidity -- they originate from tropical regions. Summer growth is easily stunted if air remains dry near the fern, especially when grown indoors. Use a spray bottle to mist the fern periodically. Alternatively, fill a container saucer with gravel and water. Place your container fern on the gravel to create a miniature high humidity climate around the pot while keeping the water from soaking the medium through the drainage holes. Although high humidity is key, soggy root conditions leads to rot and fungi proliferation. Your potting medium should be damp, but not wet.
Staghorns do not produce flowers and seeds, but use spores to reproduce. Summer's warmth stimulates spore production. Because the fern directs energy toward reproduction, summer vegetative growth can be slightly hindered -- the plant can only generate and use a certain amount of energy each day. Once spore production is complete, staghorns can redirect their energy into foliage and root growth before cooler fall and winter weather arrives.