Published on Wednesday, 30 November -0001 00:00
Fluctuating temperatures, persistent winds and lower than normal rainfall during May and June, and what appears to be following us into July, is beginning to take its toll on our landscape plants.
This is actually our fourth season of lower-than-normal rainfall, and lawns, trees, shrubs and perennials that have not received regular watering are showing symptoms of drought stress including reduced growth, yellowing, wilt, loss of branches and leaves, or in severe cases whole plant death. Many trees and shrubs, particularly those that are borderline hardy in this area, were injured or killed this past winter, due in part to drought stress during the past summers, which affected their ability to withstand the effects of a severe winter.
Because of their shallow root systems and the larger numbers of plants in a small area, the effect of inadequate moisture is more immediately apparent on annual flowers, vegetable gardens, and container gardens. The obvious solution is to apply water, but we often have to deal with community watering restrictions, well limitations, or a desire to conserve water. Therefore, we must look for ways to minimize water use and still maintain healthy landscape and garden plants.
We must begin by taking a look at our watering procedures. Following are some recommended practices for keeping plants watered adequately while conserving water.
Water deeply and infrequently. Deep watering promotes the development of a deep, extensive root system while light watering keeps the roots near the surface. Deep-rooted plants will be able to reach moisture in the soil and will be better able to survive hot, dry weather. Lawns, vegetables and flower gardens should receive an inch of water per week. Vegetables, annuals and perennials must be watered before they wilt because, if they are allowed to wilt only a few times, growth will be stunted resulting in reduced flowering and crop production. Newly planted trees and shrubs should be watered deeply every seven to 10 days during dry weather.
When watering gardens and landscape plantings, soil conditions, along with the weather conditions, actually determine the amount and frequency of watering. For example, sandy soils will require more frequent watering than clay or loam soils. Daily checking of plants is more important than a watering schedule based on calculations and charts.
Water efficiently. When using overhead sprinklers, water in the early morning. Cooler temperatures, reduced wind, and higher humidity in the morning reduce the amount of water lost to evaporation. When watering is completed, the plant foliage dries quickly, reducing the risk of foliar diseases that exists when plants are watered late in the day. Watering during the hot part of the day does not harm the plants, but is less efficient because of the amount of water that is lost to evaporation.
However, if plants are under severe drought stress, water as soon as possible to minimize plant damage, regardless of the time of day. Soaker hoses and drip irrigation systems are more efficient and promote fewer disease problems than overhead sprinklers. Drip irrigation systems require an initial investment of time and money but, once installed, are convenient and conserve water.
Mulch landscape plantings and garden areas to conserve soil moisture. A blanket of mulch reduces the rate of evaporation, maintains a lower soil temperature, and limits weed competition. Organic materials like dried grass clippings, clean straw, shredded leaves, or partially decomposed compost are good mulches for the vegetable garden. The same materials can be used for annual flowers but, if you would like something a little more attractive, try cocoa bean shells or rice hulls. In addition to the above, pine needles and ground corncobs can be used around perennials that are seldom dug and divided. Woodchips, shredded bark, or bark nuggets will work well around trees and shrubs.
Plants in containers need special attention as both volume of soil and total water available for plant use is limited. Frequency and amount of water depend on the potting mix; location, size and type of pot; size and type of plants; amount of exposure to sun and wind; and temperature. A pot that contains several plants, a pot-bound container, or a pot that contains a plant like a fuschia that demands a lot of water, may have to be watered daily or even more than once a day.
Check for soil moisture by sticking your forefinger into the potting mixture. When it feels dry below the surface, begin watering. Do not allow the potting mixture to dry out completely as this will severely stress the plants and result in poor performance. When watering, water the plant thoroughly, allowing water to drain out of the bottom of the pot. Be careful, however, not to keep the roots constantly wet as root rot and disease problems can result from waterlogged soil.
Trees and shrubs should be watered just inside and outside of the dripline, or outer edge of the plant. In foundation or border plantings, it may be more convenient to water the entire area. Soaker hoses allow for slow percolation of water into the root zone with minimum loss of water to evaporation. A quick rule of thumb is to water for one hour for each inch of diameter of the trunk of the tree. While newly planted trees should be watered whenever the soil feels dry to the touch, established trees may need watering only once every three to four weeks. Overwatering is one of the primary causes of failure in newly transplanted trees.
Lawns are best watered by overhead sprinklers. In order to maintain a green, actively growing lawn throughout the summer, it will have to receive an inch to an inch and one-half of water every 7-10 days either by rain fall or irrigation. This is a general guideline as the frequency of watering will depend on the grass species, soil texture, exposure and intensity of use. Slight wilting, a color change from green to a more grayish or blue-green shade, or footprinting are indications that it is time to water. The most efficient time to water lawns is during the morning hours from about 4 to 8 a.m. If you can tolerate some dryness and loss of green color in the lawn, a thorough soaking every 10 to 14 days will keep the lawn alive.
Watering plants during drought conditions involves a delicate balance between the desired appearance and health of the plants and the amount of water available for irrigation. Proper watering practices ensures good vegetable yields, beautifully blooming flowers, a green lawn, and survival of treesand shrubs without using excessive volumes of water. Keeping your landscape plants healthy during this time of drought will not only help with their appearance, but also prepare them for surviving another Minnesota winter.