When indoor plants go out

Flower & Garden Magazine, June-July, 1993 by Mary Ross

After a Long Winter Indoors, houseplants enjoy spending the summer in a shady spot in the garden, taking in the warm, fresh air. Most houseplants thrive outside, but the transition from cozy rooms inside to the summer garden must be carefully managed.

Books on indoor gardening rarely offer advice on how and when to move houseplants into the yard, or how to take care of them once they get there. Rushing the transition can damage plants and set back new growth. Plants need help to survive die abrupt change from the artificial climate indoors to the sunlight, wind and rain outside.

A screened porch, shady trees or a canopy of shade cloth provide the protection that houseplants need as they summer outdoors. But when you have 300 houseplants yearning to escape the confines of the house, as does Kansas City, Missouri, gardener Louanna Simmons, something on a larger scale is needed.

Three years ago, Simmons built a 40-foot pergola in her back yard to house her collection of indoor plants. Now, when her plants leave their winter windowsills and come out to the garden, they've got it made.

The pergola in Simmons' back yard, lush with tropical greenery, is an inviting outdoor room for relaxation as well as gardening chores. Each end section of the pergola is 10 by 10 feet, protected with a translucent fiberglass roof. One end serves as a potting shed, with a sink and bins for soil and supplies. Cacti and succulents are kept here, out of the rain. The opposite end is a seating area, with the tallest plants standing on the gravel floor.

Hundreds of other plants are arranged on sturdy, steel-mesh shelves in the 20-foot middle section. Shade cloth spread over the open rafters protects the plants during the heat of the day. The cloth blocks about 65 percent of the sunlight; it can be purchased at many nurseries and garden supply dealers. Panels of frosted glass on the back wall of the pergola filter late-afternoon sun and provide wind protection and privacy.

The pergola is houseplant heaven, but Simmons still prepares her plants carefully for the move outdoors in spring. She begins waking the plants up in February, using a weak (one-fourth strength) fertilizer solution.

Watch the weather, not the calendar, to decide when to take houseplants outside. It should be well above freezing, day and night. In Simmons' yard, daytime temperatures in the 60s and nightly lows in the 40s arrive in mid-May. By then, deciduous trees have leafed out enough to provide some shade, which is supplemented by the shade cloth.

It takes about a week for Simmons to move her 300 houseplants outside. She starts with the hardiest ones, saving the plants with tropical natures for last. Some plants, like African violets, are better off staying inside all year, but most others - dracaena, dieffenbachia, ivies, sansevieria, bromeliads, begonias, palms, prayer plants, ferns and ficus - make the trip outdoors.

Just like people, plants can get a "sunburn" if they are suddenly exposed to increased sunlight. Sunburned leaves turn frosty white, then brown, then black - and it doesn't go away. Chlorophyll, the green pigment in leaves, is what protects them from getting a burn. Plants grown indoors, even in a sunny room, have reduced chlorophyll levels. It takes a few days in a protected place outdoors to restore the proper levels. During this hardening-off period, the plants should receive bright light, but no direct sunlight.

The wind can be as damaging as the sun, snapping off leaves and branches, even breaking pots if plants are knocked over. A sustained wind, especially a chilly spring wind, also will dry plants out quickly. Check daily to make sure outdoor houseplants have adequate water.

Once they are outside and acclimated, Simmons groups her plants in the pergola according to their height and needs. Sun-lovers move up front; those that need more shade fill shelves along the back wall. Heavy feeders are arranged together; plants requiring less fertilizer are grouped separately. When she waters her plants, she also waters the gravel floor of the pergola to help maintain humility. Simmons is careful to arrange plants so the ones on top do not drip on those below.

Most plants should be repotted as soon as they come outside, Simmons says, but she admits the job usually takes all summer. Her potting medium is a blend of topsoil, compost, sphagnum peat moss and perlite, with fine bark or sand to improve drainage. Simmons prefers bark, and sometimes puts a cupful at a time in the blender to grind it up to the right consistency. She fertilizes monthly, and watches daily for pests and diseases. Problems can spread quickly, and symptoms require an immediate quarantine and treatment.

Simmons' plant collection grows steadily, from seeds, cuttings, trades with gardening friends and occasional purchases. She checks the plant section at the grocery store, where she recently bought a $24 bromeliad marked down to $2 because its bloom had faded. Its three fine pups went right into her houseplant collection.