by Dr. Frank Gouin

Poor Ficus benjamina

On losing its summer sun, it lost its leaves.

A friend brought her Ficus benjamina indoors after a summer outdoors. Now it has lost nearly all of its leaves.

From May until mid September, when it received nearly full sun in the morning and light shade in the afternoon, it grew a dense canopy of leaves due to TLC and quality lighting.

Now the plant is having to grow mostly in the shade, receiving only a few hours of direct morning sunlight. Only 20 to 40 percent of the leaves receive direct sunlight. The remaining foliage faces the middle of the living room. To make matters worse, the living room is seldom used, especially in the evening, thus preventing the plant from receiving supplemental lighting.

This is a common problem and the reason why I frequently advise on keeping houseplants in the house throughout the year. The foliage tissues of plants grown outdoors are very different from those of plants grown indoors. The leaf tissues of plants grown outdoors are thicker due to higher light intensity and better light quality. Also, plants grown outdoors are subjected to wind and rapidly changing temperatures. All of these factors contribute to thicker leaves and good growth.

The leaves of plants growing indoors are thinner with generally larger surfaces to maximize light absorption. Because the leaves receive only a minimal amount of light, are not regularly shaken by wind and are subjected to only moderately changing temperature, the leaf tissues are thin and weak.

The differences in thickness of leaf tissues is the principal reason why the margins of leaves turn brown when indoor plants are moved outdoors in the full sun. The leaf tissues are so tender that they are damaged by the far-red and ultraviolet rays of the sun and by drying winds.

If your Ficus benjamina defoliated after bringing it in the home from being outside all summer, leave it alone. Don’t water until it starts producing new leaves; then water only if the soil feels dry to the touch. Do not apply any fertilizer until most of the new leaves are grown to full size.