A third example is the prevention of "ugly buds" on early crops of greenhouse grown sunflowers for cutting Wien, Sunflowers are facultative short-day plants and when they are planted under natural short days the plants finish short, flower early, and develop many small "ugly buds" crowding the terminal flower bud.
Three weeks of long days 16 hours delayed flowering 18 days, nearly doubled plant height, doubled terminal flower size, and prevented the formation of "ugly buds". This approach is used with success on long-day species. Plugs are provided with long days by night-lighting beginning during the last two weeks before transplanting until flower buds become visible after transplanting. Night-lighting is not needed after early April when days become naturally long.
References Kornaski, D. Ask Dr. News , June issue, page 6. Warner, R. Supplemental lighting on bedding plants —Making it work for you. OFA Bull. Lopez R. Managing Photoperiodic Lighting. Grower Talks Magazine added Runkle E. Use of Lighting to Accelerate Crop Timing. Department of Horticulture, Michigan State University added Lighting fact sheets for greenhouse crops from Michigan State University Extension added Table 1.
Photoperiodic response groups for numerous annual bedding plants z. Supplemental lighting on bedding plants - Making it work for you. Agricultural Experiment Station. Commercial Horticulture. Environmental Conservation. Soil and Plant Nutrient Testing Laboratory.
North American Aquatic Connectivity Collaborative. Or have trouble with bolting spinach and lettuce in your summer garden? To understand plant flowering, you need to get a handle on "photoperiodism," or amount of light and darkness a plant is exposed to. The amount of uninterrupted darkness is what determines the formation of flowers on most types of plants, explained Ann Marie VanDerZanden, horticulturist with the Oregon State University Extension Service.
Botanists used to think that the length of daylight a plant was exposed to determined whether a plant would form flowers. But experiments proved otherwise. It is the length of darkness that a plant experiences that plays the most crucial role. A plant that requires a long period of darkness, is termed a "short day" long night plant.
Short-day plants form flowers only when day length is less than about 12 hours. Many spring and fall flowering plants are short day plants, including chrysanthemums, poinsettias and Christmas cactus. If these are exposed to more than 12 hours of light per day, bloom formation does not occur. Other plants require only a short night to flower. These are termed "long day" plants. These bloom only when they receive more than 12 hours of light.
Many of our summer blooming flowers and garden vegetables are long day plants, such as asters, coneflowers, California poppies, lettuce, spinach and potatoes.
These all bloom when the days are long, during our temperate summers. And some plants form flowers regardless of day length. Botanists call these "day neutral" plants. Tomatoes, corn, cucumbers and some strawberries are day-neutral.
Some plants, such as petunias defy categorization, said VanDerZanden. Horticulturists and home gardeners manipulate the day and night length indoors with lights to get plants to bloom at times other than they would naturally. For example, chrysanthemums, short day plants, naturally set flower and bloom with the long nights of spring or fall. But by making the days shorter by covering the chrysanthemums for at least 12 hours a day for several weeks over the late spring and early summer, you can simulate the light and darkness pattern of spring or fall, thereby stimulating summer blooming.
Or you can bring a long-day plant into bud formation and eventual bloom early before our day lengths surpass 12 hours. Put the plant under grow lights for a few hours a day beyond natural day length for a few weeks. Adding supplemental day length to stimulate early blooming is a common practice in the nursery and fresh flower industry, especially this time of year, for Valentine's Day and Easter flowers.
Another popular plant that is day-neutral is the tomato plant Lycopersicon esculentum. Within each group of long- or short-day plants there is another division that puts some plants into two smaller groups: qualitative or quantitative plants.
These are plants that require a certain number of nights or days to perform a specific task. For instance, poinsettias Euphorbia pulcherrima require a set number of nighttime hours to have the bracts turn red. This is known as a qualitative plant. A quantitative plant will flower or set fruit whether or not the light and dark hours are reached.
However, the plant performs best when exposed to a set number daylight hours. For instance, rye Secale cereale does well, but produces more seed when exposed to long days.
Julie Richards is a freelance writer from Ohio. She has been writing poetry and short stories for over 30 years, and published a variety of e-books and articles on gardening, small business and farming. She is currently enrolled at Kent State University completing her bachelor's degree in English. By Julie Richards Updated November 25, Related Articles.
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