Download the audio of Yard & Garden News: MP3, WMV.
Help Your Garden Cope with Dry Spell
Dry summers are not unusual in Indiana. In fact, I addressed dry conditions in this column just two years ago. Gardeners struggle hard enough to maintain healthy plants when extreme high temperatures are accompanied by lack of rain. What compounds the stress of this year's dry weather is that it follows the wild weather extremes experienced earlier this year.
March brought unseasonably warm temperatures to lure plants out of dormancy, and then April put the freeze on many of those plants. So some plants that may have already been struggling to get by could be finished off by the current hot, dry weather, unless gardeners come to their rescue.
During prolonged dry conditions, community water restrictions may require gardeners to limit watering and prioritize which plants will get first aid. Newly planted trees, shrubs, flowers and vegetables are at greatest risk of injury. Most gardeners are accustomed to watering flowerbeds and vegetable gardens regularly. These plants require approximately 1 to 1 1/2 inches of water per week to maintain optimum flowers, foliage, roots and fruits.
Established plants may tolerate 10-14 days between waterings but be aware that problems, such as fruit cracking and blossom end-rot, will increase. Watering is most critical at pollination and fruit-set time. Apply mulch where possible to conserve what moisture there is, and reduce competition from weeds.
The best way to irrigate plants is to gently soak the soil with the prescribed amount of water in one application. This deep watering encourages deeper root growth, which in turn will be better able to withstand dry spells. Frequent shallow watering, on the other hand, encourages shallow roots, which are more likely to succumb to heat and drying of the topsoil. Sandy soil and container plants need more frequent irrigation.
The time it takes to apply the proper amount of water depends on how much water pressure you have, the amount of space you need to cover, air temperature and wind speed. You'll need about 50 gallons of water to apply 1 inch of water to a 100-square-foot area.
Leaf scorch on trees and shrubs, which appears as browning of leaf edges, is very common in most dry summers. Couple that with the spring freeze injury and many trees and shrubs are dropping leaves before they turn brown.
While minor cases of leaf scorch and leaf drop are not terribly harmful to the plant, prolonged lack of moisture can spell disaster for landscape plants. Young and newly established plants are most susceptible to the dry conditions, but even established plants may reach a critical point during prolonged drought. Branch and root dieback make plants more susceptible to winter injury. Plants already stressed by other factors may succumb to severely dry soils.
Keep in mind that next year's growth will be determined by buds that form this summer and early fall. Flower buds for many spring-flowering and fruiting plants will also be developing during this time. So even if your plants aren't showing any symptoms now, the damage may become apparent next season.
Watering landscape and fruit plants should be aimed at where the roots naturally occur. While these woody plants have some roots that grow very deep, most of the feeder roots that are responsible for water uptake grow in the top 12-18 inches of soil. Most feeder roots are concentrated below the dripline of the foliage canopy and outward, not up close to the trunk. Allow water to thoroughly soak the target area by applying water at a slow enough rate to allow penetration rather than wasting water as runoff. Apply the water no faster than 1 inch per hour. As with annual plants, applying mulch will help prevent moisture loss due to evaporation.
The ideal time to water is before 8 a.m. This makes maximum use of water while allowing foliage to dry. Midday watering when temperatures are high, sunshine is strong and winds are brisk wastes substantial water. Watering during the evening or overnight can make plants more susceptible to disease infection by providing the surface moisture needed by fungi and bacteria. Of course, if your community imposes restrictions on water use, ideal watering practices may not be possible. If your community is under restricted water use, it is certainly better to water when permitted than not water at all.
Household gray water, such as that leftover from the bath or washing dishes can be used, within limits, if fresh water is not available. Detergents in gray water contain salts that can accumulate to harmful levels in the soil. Use gray water only as a last resort, and use it as sparingly as possible to avoid salt build up. Never use gray water on edible crops or on containerized plants.