For many years specialists have recommended putting houseplants outdoors for the summer. The good light and natural growing conditions of the outdoors are what they need after a winter of poor light and dry air in the home, they said. "Plants will thrive (outside), double in size and regain full vigor for another season beautifying the home during the winter."
Research has indicated it may not be such a good idea for foliage plants but perhaps may provide a needed boost for plants that bloom such as gardenia and minature orange (Citrus mitis).
Most foliage plants sold in the USA are grown in Florida and California under much higher light intensity than is found in the average home. Under those conditions, the plants have small, thich light-green foliage (sun leaves). The leaves that develop in shade are large, thin and dark-green.
Many of the foliage plants now being grown are acclimatized before being placed on the market. That is to say, they are adjusted to the change in environment they will find in the home.
Unless acclimatized, the plant quickly drops its sun leaves after being taken into the home. If it survives, it will have acquired new leaves that are shade tolerant.
If the plant goes outdoors for the summer and receives a lot more light than it was getting in the home, it is likely to be thrown completely out of adjustment.
Three outstanding authorities were asked to comment on this: Dr. Henry M. Cathey, chief, Florist and Nursery Corps, USDA Agricultural Research Service (also president, American Horticultural); Dr. Charles A. Conover, director, University of Florida Agricultural Research Center, Apopka; and Dr. D.C. Kiplinger, professor of horticulture, Ohio State University.
"It's okay to place the plants in the out-of-doors," says Cathey, "if you (1) maintain dense shade much like the interior lighting, (2) heal out plant (remove it from pot) poke holes in the soil ball and pat in fresh soil, (3) deflect some of the rainfall (cover the soil with plastic), and (4) maintain moderate fertilizer levels."
"Most gardeners ruin their house-plants when they move them outside from a dim to a bright location. Yellowing and leaf drop occur immediately. Then - slowly - the plants (some of them) revive. You start all over. Our recommendation is as follows," says Conover, "When placing foliage plants outdoors during summer, do not place them in more light intensity than they can tolerate. What can they tolerate? That depends on the level they received indoors.
"Actually, you can hardly ever place them in full sun, and in most instances, they need to be in moderate to heavy shade.
"If a plant is growing well indoors, there is really no great benefit to be gained from placing it outdoors. However, if it is under stress indoors, and light is a factor, it will often help to place it under higher light of a shaded porch, etc."
"I don't think you could really call taking the plants outdoors giving them a vacation as such," says Kiplinger. "While true enough it may restore vigor because of the more favorable environment outside compared to indoors, particularly with respect to light, this really wouldn't be a vacation.
"Most foliage plants when grown inside and then taken out would certainly not tolerate being placed in full sun. The leaves would just simply burn and turn brown or bleach so badly they would be very light green due to destruction of the chlorophyll by the light.
"Therefore, when plants are taken outside, one should be careful that they are not placed in too exposed a location, but even then if placed under trees or something of this nature, generally this is better light than you find in any places in the home where plants are grown."
In summary, a lot of discretion should be exercised in putting foliage plants outdoors for the summer.