The Right Amount of Light for House Plants

In their natural environment, plants grow in light that best suits their needs. If they are to thrive as house plants they should be placed in a position that resembles their natural conditions as closely as possible.

There are three factors that influence the light that plants receive: the amount of light that is available each day; the intensity of the light; and the quality of the light. Each of these plays an important role in maintaining the health and appearance of plants.

Duration of light

The length of the period of light, compared to that of darkness, influences the flowering period of many plants. Some plants begin to develop flower buds when the period of darkness is longer than the period of light. These are known as short-day plants.

Others start to form flower buds when the period of light is longer than that of darkness, and are known as long-day plants. In some cases the duration of light is not important—the plant’s ability to flower may depend on its age or some other factor.

Intensity of light

The intensity of natural light is influenced not only by the time of day, but also by the time of year and the direction the natural light comes from. The intensity is always stronger in the summer months, while a southerly aspect allows more light to enter the room than a northerly one.

Quality of light

Sunlight is vital to the growth of plants because it initiates the chemical processes of growth. A standard tungsten-filament light bulb does not produce the type of light rays plants need for growth, and in fact these light bulbs may burn a plant if they are placed too near it. However, fluorescent tubes provide an artificial source of light that can be used to supplement the amount of available sunlight.

Too much light

• Light hat is also very strong will burn the leaves, especially if you splash water on them.
• Causes brown or grey scorch marks on the leaves, usually towards the tips.
• Causes the leaves of plants that like partial shade to shrivel.
• Causes the leaves to become pale, giving them a bleached appearance.
• May cause the plant to transpire (give off water) too quickly, which in turn may cause it to wilt during the hottest part of the day.

The fluorescent factor

Fluorescent light enables you to grow plants that normally need a good deal of sunlight in the gloomiest corner of the room, or bring them into bloom in the dull months of winter. Although flowering plants benefit most from artificial light, foliage plants will also be healthier under such conditions.

Low-growing plants are the most suitable types for growing in an indoor ‘light garden’, as the light is suspended above them. Saintpaulias, peperomias, cinerarias, small begonias, gloxinias and bromeliads are some of the most popular plants grown under artificial light.

In general, fluorescent lights should be left on for 12-16 hours a day, but do remember that different plants have different needs; extra light may induce some plants to flower, but in other cases it may prevent the production of flower buds.

Using artificial light

Artificial lighting for house plants can consist of two 40-watt fluorescent tubes suspended above the plants. One should be a daylight tube, the other a cool light tube.

Alternatively, you can use two Gro-lux tubes. The tubes should be suspended 30-60cm ( 12— 24in) above foliage plants, and 15-30cm (6-12in) above flowering plants. Stand your plants on a tray of moist pebbles to keep the air around the plants humid.

Insufficient light

• Causes the leaves of variegated plants to lose their markings and turn completely green.
• Prevents flowers from developing to their full size, or prevents flower buds from developing at all.
• Causes the new shoots to become spindly, or `leggy’, with long intervals between each of the leaf joints.
• Prevents the leaves from developing to their full size.
• Causes the upper leaves on the plant to become pale, and may also cause the lower leaves to turn yellow, become dry and then drop.

Getting it right

Giving your plants the right amount of light for their needs is an important aspect of house plant care. Too much or too little light can have serious effects on their health.

To keep your plant healthy and attractive, make certain that it has good light.

Checklist

Don’t

• Position your plants near spot lights, as they may burn them.
• Leave plants, especially those with a symmetrical shape, in one position, as shoots grow towards the light and will bend if the plant is left in the same place. To prevent a plant developing a lop-sided shape, turn it a little every four or five days.
• Move a flowering plant from bright light to a shadier position; if you do, it will not produce the same number and quality of flowers.
• Position variegated foliage plants in shade. The variegations of the leaves will disappear if you put your plant in a dull spot.

Do

• Keep windows clean, especially during winter. Dirty windows can reduce the available sunlight by up to 10 per cent.
• If possible, remove net curtains from windows in winter, to allow more light in.
• Move plants nearer to the window in winter, but avoid draughts.