Many plants will perform tolerably well in an indoor setting, provided they are given adequate light. Most plants sold as "indoor plants" need considerably less direct light than sun-loving plants, many flowering plants or vegetable species; however, many artificial lighting options are available on today's market. With good lighting, ventilation and water, plants can continue to put on lush, healthy new growth.
Signs of Healthy Plant Growth
Regardless of whether they are grown indoors or outdoors, in sun or in shade, the outward appearance of a healthy plant is essentially the same. A plant growing with optimum lighting, nutrition and drainage will have robust, vibrant-colored leaves, roots with a white to yellow color and a fresh scent, and a strong central stem with shorter, rather than longer, intervals between leaf nodes. Plants growing in poor lighting are typically leggy and spindly, with a stretched appearance, weak and floppy stem, and pale or sickly looking leaves.
About Lighting and Plant Growth
Along with water and air, lighting is one of the three non-negotiable requirements for healthy plant growth. Sun-loving plants usually require six or more hours daily of bright, direct light to remain healthy and reach its optimum growth potential; vegetables and many flowering perennials are good examples of plants, which need a long period of direct lighting each day. Plants that need fewer than six hours a day of direct sunlight are usually called semi-shade or semi-sun plants--the terms are more or less interchangeable--and many of these types of plants will grow well in dappled shade, or with only a few hours of direct light per day. Plants for shade perform best when very little strong direct sunlight hits their leaves, such as many types of ferns, hostas and annual flowers like impatiens.
Artificial Lighting for Plants
Gardeners who grow vegetables from seed, or who keep tropical plants indoors, know that replacing the sun's strong rays during the unseasonable winter months is an essential part of keeping plants alive and healthy. Fluorescent tube lighting is among the most economical methods of providing light for plants indoors, both during winter and year-round. Different spectra can be used depending on whether the gardener is attempting to start seeds or to encourage a flowering plant to bloom. Apart from lighting, ensuring that a plant growing indoors has adequate moisture, humidity, nutrition and in the proper temperature range is also essential for good health.
Importance of Light Color
Natural sunlight, which appears white in color to the human eye, is composed of a spectrum of colors in different wavelengths from red to indigo--what we know as the rainbow. Plants mainly use only two of these wavelengths, red- and blue-wavelength light. Fluorescent tube lighting is mostly blue wavelength light, though some lights have been designed to emit a mixture of red- and blue-spectrum light, which is thought to be necessary for flowering plants to produce blossoms. Incandescent lights are unsuitable for providing light for indoor plants, as they burn hot and emit light in the yellow and orange spectra, according to the Oregon State University Botany Department.
Light Strength and Duration
To match natural sunlight, most artificial lights must be rather close to the plant. Generally, artificial lights situated over plants grown indoors should be no farther away from the plant than 8 to 12 inches, as the light's effectiveness diminishes greatly with every additional inch. Lights placed too far away cause plants to become long and spindly.
For growers concerned with encouraging plants to flower, knowing the plant's preferred "photoperiod" is essential. Long-night plants are spurred to bloom when the nights become longer, and usually begin blooming when the nighttime period is between 11 and 14 hours. Short-night plants, by contrast, usually need less than 10 hours of darkness to flower. Additionally, some plants are neutral, or indeterminate, and will flower year-round regardless of the length of the night.
Transitioning from Indoors to Outdoors
Many plants grown as indoor plants can also be used under similar situations outdoors, but timing and preparation are key. Especially for plants used to mostly shady conditions, the outdoor area where the plant is to be placed should be similarly shady. Plants that are to be grown under sunlight, need to be gradually exposed to the sun's rays, or "hardened off." Setting plants out for increasingly longer periods of time each day over the course of a week or two allows the plant to grow a protective waxy cuticle over the leaf surface, which protects it from harmful rays, drying winds and excessive wilting through evaporation. Outdoor temperatures should be well above freezing before beginning the hardening-off process.