The basics of watering your landscape

Watering home landscape and garden plants properly is one of the most misunderstood tasks facing most gardeners today and often the cause of many plant deaths.

First, you need to understand how a plant loses water.   Transpiration is the process by which a plant loses water through its leaves. This is a necessary process for plant growth. A large tree may lose hundreds of gallons of water a day in the summer. Water lost from the soil by evaporation and transpiration must be replaced by precipitation or irrigation.   Water may also evaporate from the soil surface, leaving it dry. Water from lower layers in the soil is drawn to the surface by capillary action and also evaporates. This continual evaporation may deplete water from quite deep in the soil.

Establishing the correct water-air relationships in the soil is essential for the best growth of all plant types. Oxygen in the soil is necessary for plants to grow. Watering too often or too much is likely to exclude the necessary oxygen from the soil pore spaces. Without enough oxygen, plant roots suffocate and die. Plant parts above ground exhibit symptoms of this stress: wilting, yellowing, and drying foliage, leaf drop and twig dieback may all occur. Constant overwatering kills most plants, too! In both cases, either too much or too little water, the plant suffers from lack of moisture in its tissues.

A good rule-of-thumb to follow in watering plants is to fill the entire root zone with water, and then allow the soil to dry out partially before the next irrigation. The amount of drying depends on the plant species and size. Large trees and shrubs can be allowed to dry several inches down in the soil before rewatering. A small or newly established plant will need watering before very much soil drying takes place.  To assess soil moisture, simply take your garden trowel and dig down approximately 6-8 inches, this is especially important if the area is mulched.

It is essential that gardeners become familiar with how long it takes the root zones of the various plants in their gardens to become completely moistened, and then, how deeply they can allow the soil to dry before the plants begin to show stress and need rewatering. It is also necessary to understand that quick, light sprinkling will not do the job of wetting the entire root zone.

Vegetables, bedding plants, and perennials are usually small when planted and have comparatively shallow roots. These plants may have to be watered more often to ensure a healthy root system. The entire root zone should be moistened before the plants show signs of wilting. If the plants are allowed to wilt a few times, growth will be retarded and harvest yields reduced. Be careful not to overwater.  Soaker hoses can be a great addition to the home garden.

Plants in containers need special attention. Both volume of soil and total water available for plant use are limited. These plants have to be watered more often than plants growing in the ground. Watering should begin when the soil surface feels dry to the touch, but not before.

Containers which have been allowed to completely dry out may need to be soaked in water to re-wet the soil.

Trees, shrubs, and landscape plants should be watered just inside and outside the dripline, or outer edge of the plant. In foundation or border plantings, it may be more convenient to water the entire area.

Shrubs and trees near house foundations, under eaves, and/or in southern, southwestern, or western exposures have to be watered more frequently. They may get little water from precipitation, and reflected heat from walls leads to increased water and heat stress.

The soils in which balled and burlapped and containerized plants have grown are often radically different than the soils into which they are planted in the home landscape. Therefore, it is most important that water be applied to both the nursery soil and the surrounding soil during the critical establishment period. Roots grow only where there is moisture, and unless both media are moist the roots may never grow out of the original nursery soil. Plants in such a situation may ultimately girdle themselves and die.   If you need more help with watering your plants or have additional plant questions, please feel free to call OSU Extension in Fairfield County at 740-653-5419

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