GROW ON-COLOR PLANTS--NOT OFF-COLOR PLANTS

Have you ever wondered why nursery stock, especially the ones grown under cover, are more vigorous and on-color than shrubs, ground cover and other plants growing in the landscape?

The real world environment has non-optimum conditions--too hot, too cold, water deficiency, salinity and other stresses. The healthy appearance of a plant is a direct function of its sturdy establishment and its ability to overcome limiting conditions.

Multiple stresses occurring simultaneously are more severe on plants than if they occur individually. For example, cold hardiness is lessened in the presence of excess salinity as is heat tolerance. "It has been estimated that more than 50% of all plant diseases are [intensified] by improper environmental, nutritional, or physical conditions[1]." Healthy plants can resist pathogens much better than stressed plants.

Solar radiation is essential for photosynthesis. Green leaves intercept sunlight to produce plant sugars from carbon dioxide and water. Since sunlight also heats the plant tissues, plants transpire water for cooling purposes. Special leaf pores called stomata are the sites of the evaporation. These same pores are the location for the entry of carbon dioxide which is used by the plant for sugar production. When drought stress occurs, these pores close to conserve moisture. However, concurrently the plant starves since metabolic energy will not be produced. As a protective mechanism to lower the temperature, the leaves droop and the plant wilts, lowering the angle of incidence to sunlight to decrease solar heating. Defoliation is another protective mechanism against excess water loss.

Adequate plant moisture depends upon the absorption of water by the roots. Water may move to the roots or root growth may intercept moist soil. As soil moisture decreases, liquid flow stops and water moves through the pore space or voids as a vapor. Compacted soils with less voids restrict vapor movement and limit root exploration for moisture. Since water moves rapidly along root hairs, good root growth makes a plant more drought resistant. Good soil physical properties allow for deep rooting which provides additional moisture and enhances plant appearance.

Plants Under Water-logging Conditions May Behave Like Plants Under Drought Conditions

It is interesting to note that flooding injury has some similar symptoms as water deficiency. Oxygen-limited roots are unable to function properly. Studies have shown a 30% to 40% decrease in water movement in plants under this condition. Plants can wilt. Other symptoms are new root formation from stems and yellowing of leaves from the base to the top of the plant.

To help insure on-color plants, soil properties need to be enhanced. This will minimize unfavorable interactions from multiple stresses. One excellent method is that of water-soluble soil polymers which increase pore space in soil and enhance the growth of plant roots. Other than for sands and a very few sandy loams, all soils can be greatly improved through the use of SOIL DRAIN water-soluble PAM to increase the physical structure of soils.

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[1] "The Physiology of Plants Under Stress,” M. G. Hales and D. M. Orcutt, John Wiley & Sons, New York, 1987