Leaves must have Light
Leaves are the plants’ food factories, and light is the power that helps them manufacture food from elements of air and soil. Most plants need many hours of sunshine daily in order to grow satisfactorily. Roses, for instance, need at least six hours. Some plants, however, get along with little light, so they can grow in shade or semishade.
A good general rule to remember is that ordinarily the more sun a plant gets, the better it will flower.
Morning sunlight is kind light, bright but relatively cool; thus the east side of your house is a favored position for plants.
Afternoon sunshine is hot and harsh, so a western exposure is less versatile.
Sun touching and warming the soil is desirable in early spring, to start plants into growth. And it’s good all year in cool climates. But in hot-summer areas, it can dry the earth and overheat roots, so plants often require part-time shade, or being close enough together to shade the ground, or having a protective carpet of groundcover plants.
Light
Light affects plant life in many ways. The scientific name for the process by which green plants use light energy to synthesize carbohydrates (foods) from carbon dioxide and water is “photosynthesis,” from the Greek words photos, meaning light, and synthesis, meaning putting together.
Light supplies the energy needed to transform carbon dioxide absorbed from the air, water, and certain inorganic minerals into organic matter and into the oxygen, which the plants give off as long as light is present. Where light is absent, photosynthesis stops, and the plants absorb oxygen and give off carbon dioxide.
Research has resulted in the classification of plants according to their day-length characteristics. One group, “short-day plants,” flowers when days are short and nights are long. “Long-day plants” flower when days are long and nights are short. Still others are unaffected by day lengths and are called “light neutral” or “indifferent.”
The following list includes common flower and vegetable plants according to their light requirements.
Short-day plants (10 to 12 light hours)
Asparagus
Aster
Beans
Carrot
Chrysanthemum
Corn
Dahlia
Gardenia
Poinsettia
Potato (tuber development)
Strawberry geranium
Sweet potato
Long-day plants ( 14 to 18 light hours)
Most annuals
Beet
Chicory
Chinese cabbage
Dill
Grains
Hibiscus
Onion
Pea
Radish
Spinach
Tuberous begonia
Indifferent plants
African violets
Kale
Kohlrabi
Broccoli
Lettuce
Brussels sprouts
Marigold
Cabbage
Cauliflower
Spinach
Celery
Okra
Coleus
Pepper
Collard
Rose
Cress
Semperflorens begonia
Cucurbits
Endive
Tomato
Geranium
Turnip
Regulating Light in the Garden
Outdoor gardeners can improve their results by increasing the amount and the consecutive hours of light their plants get. A white mulch (such as light stones), a white painted building or fence or strips of aluminum foil placed in the garden will reflect more light energy onto plants, spurring them to greater growth. Fruit growers can prune out the center of their trees to increase flower bud formation by getting more light to the center of their trees.
Light also affects the germination of seed. Some seed germinate more readily when exposed to light than when buried in the earth. Grasses, lettuce, celery, snapdragon, petunia, and flowering tobacco will all be more successful if seed are merely pressed down or gently watered down into the growing medium.