We are
now in the fall months. Cooler temperatures are upon us with the cold winter
days coming. In addition to the temperature changes, the days are getting
shorter, which has an impact on many plants. Many of the deciduous trees and
shrubs have foliage that is becoming colorful. The cooler temperatures are part
of the reason for this phenomenon, but also it is a reaction to the shorter
days. ‘Photoperiodism’ is the term used to describe a plant’s response to the
length of day and night. Because the plants produce seeds, flowering is
important plants to complete their life cycles. They can be divided into short
day plants, long day plants and day-neutral plants.
Short day
plants are induced to flower when the lengths of the nights are greater than
the days. You may have noticed that many wildflowers are in bloom now that were
not earlier in the season. A better way to describe them is long night plants
since the period of darkness is what stimulates the plants to flower. The less
light promotes them to produce more flowers and fewer leaves and stems.
Principal agriculture crops that are short-day plants include cotton, rice, and
soybeans. Also, chrysanthemums, dahlias, goldenrods, asters, and poinsettias flower
when the days shorten. For individual floral crops, flowering can be induced by
imposing artificial darkness on them. In greenhouses, growers cover their
plants with a dark curtain to block out light to increase the amount of
darkness to induce flowering. Any disruption in the dark period will interfere
with the production of flowers. A result of this process is the availability of
chrysanthemums and other short day plants in stores throughout the year.
Long day
plants respond to shorter nights and longer days. They flower in the spring and
early summer. Examples include peas, barley, lettuce, and wheat. Also, many of
the vegetables that are planted in the fall begin to flower in the spring as a
result of increased day length. Cabbage, collards, kale, mustards and other
similar crops develop flowering stalks in the spring in a process referred to
as bolting. The vegetables lose their flavor when this happens. Poppies,
petunias, and larkspur are also long day plants.
Day
length does not influence the flowering of day neutral plants. Instead, they
begin to flower after reaching developmental stage or age, or in response to
environmental conditions such as a period of cold temperatures. Cucumbers,
roses, tomatoes, beans, and potatoes are day neutral plants.
Plants
are complex organisms with a multitude of important physiological process. No
two species are exactly alike. Many factors influence their growth and ability
to produce flowers, fruits, and seeds. The amount of daylight and the length of
nights are important to many plants, including important agriculture crops and
ornamentals.
Poinsettias are am example of a short day plant
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