Great Plains Gardening
July 9, 2004
Have you ever considered what causes your plants to grow as they do? Most of us just plant the seed or transplant seedlings from the garden center in shady or sunny areas as directed on the labels or seed packets and never give a thought as to how they actually grow.
Would you be surprised to know that plants have hormones? Understanding how hormones work allows horticulturists to manipulate plants for specific purposes. Plants produce hormones from the energy that is produced from photosynthesis and the nutrients from the soil and air. Conditions of the environment, such as light, heat, touch and water can trigger hormonal responses in plants that affect their growth. When the nutrients are lacking in your soil the chance for hormonal deficiency increases. When certain characteristics appear, the alert gardener can determine what is lacking and correct the nutrient balance.
Auxin is one of four growth hormones produced by the plant. "Auxin produced in the rapidly growing terminal buds suppresses growth of side buds, giving a young tree a more upright form. As growth rates slow with age, reduction in apical dominance gives the maturing tree a more rounded crown. Auxin also stimulates root growth and also plays a key role in tropism (controlling the direction of plant growth). In phototropism the auxin concentration on the shaded side stimulates cell elongation, turning the stem to the sun. In geotropism, under the influence of gravity, auxin accumulates in the lower side of a horizontal stem, causing cells to enlarge faster, turning the stem upright.
Gibberellins affect the rate of cell division, flowering, increase in size of leaves and fruits, seed and bud dormancy and induction of growth at lower temperatures. Gibberellins produced in the root growing tips, stimulates shoot growth.
Cytokinins promote cell division and influence cell differentiation and aging of leaves.
Abscisic acid is considered the "stress" hormone. It inhibits the effects of other hormones to reduce growth during times of plant stress.
Quality, intensity, and duration of light also directly impact plant growth. Light quality refers to the color or wavelength reaching the plants surface. The rainbow is an example of the colors into which sunlight can be divided…red, orange, yellow, green, blue, indigo and violet. Red and blues have the greatest impact on plant growth, while green light is least effective. The reflection of green light gives the green color to plants. Blue light is responsible for leaf growth and the red light combined with the blue encourages flowering.
Light intensity refers to the amount of sunlight a plant receives. The more it receives the higher the photosynthetic rate will be. If plants that have been growing in low light are moved to a bright location they will be susceptible to sun scorch. Over time, as the wax content on the leaf increases, it will become more sun tolerant.
Light duration refers to the amount of time that a plant is exposed to sunlight. Travelers to Alaska often marvel at the giant vegetables and flowers that grow under the long days of the arctic sun even with cool temperatures. The length of uninterrupted darkness controls the flowering response of many plants. There are three types…Short day plants that respond to long periods of darkness such as chrysanthemums and single crop strawberries; long day plants that respond to a short period of darkness such as onions and spinach; and the day neutral plants that flower without regard to the period of darkness, but usually are more prolific under the influence of long daylight times.
These are some of the things that were covered in the Botany section of our Master Gardener training sessions.
Until next time…