Water! Water! Water!

Kathi Mecham

The high temperature and high humidity conditions have many plants struggling. From tomatoes to maples, all species need additional water during drought. Despite the wet spring we had, watering now is essential.

In the best of times, we need to provide vegetable and flower gardens with adequate water. In times of 105-degree heat index we need to think about watering all trees, shrubs, and plants in our yards.

Mature trees and shrubs

Many large mature trees are experiencing stress due to weather conditions. Excessive spring rains created saturated soils. Root systems can be damaged by water-logged soils. Damaged roots compromise the trees health and weaken the plant. Weakened trees already suffering from stress, are more susceptible to insect damage and disease.

Loss of leaves is one sign the tree is stressed, and lack of adequate moisture may be part of the problem. Drip irrigation is the most effective way to water. It puts moisture where it is needed, into the root zone of the tree. Sprinkler irrigation is not effective at getting the water into the root zone. It also wastes water and can lead to fungal leaf disease.

Newly-planted trees and shrubs (1-5 years)

Drip irrigation is also the most effective method for watering new trees and shrubs. The first year is critical. Subsequent years are important too, especially during drought conditions. Frequent, light, applications to the root ball are vital. The roots are developing and growing outside the root ball and until they are established applying adequate moisture allows for less stress. There is a balance of applying the right amount. The clay soils in many areas can become water-logged leading to damaged roots, compromising the health and growth of the new plant.

Herbaceous perennials

Purple coneflower, black-eyed Susan, and Shasta daisy are plants that die back to the ground in winter, but the roots are still alive. Once established, they do not require as much water as annual plants but, they still need adequate moisture to keep them healthy and flowering. In times of drought, it is especially important to provide additional water. A drip hose can be placed in a garden, and it is very effective and can save water. Often watering by hand is the method used in gardens. A gentle stream at the base of the plant is most effective. Avoid overhead watering if possible. Watering overhead can split the plant, damage the flowers, use more water, and allow for wet foliage, leaving the plant more susceptible to disease.

Annuals plants and flowers

Geraniums, petunias, begonias, marigolds, zinnia and more make for a cheerful and colorful yard. In times of drought, they sometimes need to be watered every other day if they are not receiving rain. Again, the best approach is either a drip hose or a gentle watering near the root zone. If plants are in containers or hanging baskets they may need to be watered daily.

Vegetable garden

Annual vegetable plants should be watered like annual plants and flowers. To produce healthy produce regular watering is needed. Adequate moisture and watering at the root zone are critical to keeping disease at bay. Wet foliage on many vegetable plants can lead to powdery mildew or other fungal disease.

All plants

Trees, shrubs, and flower gardens all benefit from mulch. Mulch helps to keep the soil cool, reduces evaporation and suppresses weeds that compete with moisture.

More information on the different types of mulches and the benefits can be found at https://extension.missouri.edu/publications/g6960.

Early morning is the best time to water. Watering during the heat of the day leads to evaporation and the possibility of leaf scorch. Watering in the evening does not allow time for water on plant foliage to dry therefore providing an environment for powdery mildew and other disease. Remember plants need moisture going into winter too. Water thoroughly in the fall before the first frost especially evergreen species. While other trees are dormant in the winter, evergreen plants still transpire (release water) and moisture is important so that they do not dry out.

For an in-depth guide on how to water large mature trees, irrigation methods and systems see https://www.kansasforests.org/forest_health/health_docs/irrigationtreeshrub.pdf For more information on watering or other horticulture topics contact Kathi at mechamk@missouri.edu or 660.542.1972.

Kathi Mecham is a Field Specialist in Horticulture, NW Region for the University of Missouri Extension.