Master Gardener: Hormones have profound effects on plants
BY BILL SEVIER Ask a Master Gardener
Saturday, December 01, 2012
12/01/12 at 5:40 AM
Q: I read, surprisingly, plants have hormones. Do they have hot flashes? Myrna C., Tulsa
A: Plants do have several important hormones that may have multiple effects on a plant's growth and development. We all know that sometimes plants seem to be temperamental, but so far hot flashes have not been identified.
Hormones in plants are much smaller and simpler than those in mammals, but their effects on plants may be profound. Our knowledge of these hormones explains a lot of the plant behaviors we see and also has led to the development of effective herbicides and important compounds called plant growth regulators.
There are at least five major plant hormones: abscisic acid, auxin, cytokinins, ethylene and gibberellins. They have many complicated effects, and without these hormones, plants would simply be unrecognizable globs of green tissue.
Auxin was one of the first plant hormones discovered and best understood. It is mainly produced by growing tissues at the end of limbs and stems. It stimulates stems to grow longer and roots to expand. It also prevents growth of side buds on stems below their tips. Removing limb tips allows side buds to grow and new sprouts to develop.
This effect explains why recently pruned or damaged shrubs or trees produce new growth of limbs and suckers. This effect is used to increase desirable density of some plants. It also is the reason trees damaged during the 2007 ice storm developed so many suckers.
Concentrated auxin is also sold as a root stimulator. It is a white powder plant cuttings are often dipped into to promote new root development.
Derivatives of auxin are used as herbicides. One of the most commonly used herbicides, 2,4-D, has a powerful growth stimulating effect in plants, especially broad-leaved weeds. The plants grow so fast it kills them. This effect is one of the reasons that 2,4-D type herbicides are most effective in spring and fall when weeds are actively growing.
There are many other practical uses of plant hormones. One that many people are familiar with are the chemicals that utility companies use to prevent trees from growing into power lines. One plant growth regulator used is called Cambistat. This reduces the growth rate of trees and appears to be safe and even beneficial. The energy saved by not growing taller can be used to produce more roots and to help the plant resist disease.
So, even with no hot flashes, hormone effects are interesting. Fortunately we do not have to contend with the question of hormone replacement therapy in older trees.
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Original Print Headline: Plants have hormones, too
Cover strawberry plants with a mulch about 3-4 inches thick if plants are prone to winter injury. Straw or similar material without weed seeds is a good choice for a mulch.
Wait to prune fruit trees until late February or March. This applies to most trees and shrubs, the exception being spring blooming shrubs that should be pruned, if needed, after blooming is complete.
Perform routine maintenance on lawn mowers - drain gas, change oil and spark plug, sharpen blades. Clean, sharpen and store other garden tools.
Although plants have several important hormones, it's safe to say these aren't the kind that cause flushes and hot flashes. But if they did, it might look something like the beautifully "flushed" Red Oriental lily. BILL SEVIER/Courtesy