Rainfall in portions of Iowa have been well below normal over the last three months. Plants will need to be watered in dry areas to ensure a bountiful vegetable or fruit crop or an attractive landscape. Two important aspects of watering are frequency and timing.
According to Richard Jauron, horticulture specialist with Iowa State University Extension and Outreach, most flowers, vegetables and fruits perform best when they receive 1 to 1½ inches of water per week (from either rain or irrigation). A deep watering once a week should be adequate for vegetable, flower and fruit gardens in dry weather.
Plants growing in containers should be checked daily in summer to determine if they need to be watered. If uncertain about the need to water, poke your finger into the potting mix. Water the container when the potting mix is dry at the 1-inch depth. Plants in small containers may require daily watering in hot, windy weather. When watering plants in containers, continue to apply water until water begins to flow out the drainage holes in the bottom of the container.
Do not allow the potting mix to dry out completely. Potting mixes shrink and pull away from the sides of the containers when completely dry. Dry potting mixes are difficult to moisten, as water tends to flow between the potting mix and container and then out the bottom of the container (while the potting mix remains dry). Containers that have been allowed to dry out completely should be placed in a tub of water for 20 to 30 minutes to remoisten the potting mix.
Individuals have two basic options regarding lawns when confronted with hot, dry weather. One option is to do nothing and allow the grass to go dormant. The alternative is to water the turfgrass during dry weather to maintain a green, actively growing lawn.
Cool-season grasses, such as Kentucky bluegrass, can survive long periods of dry weather. In dry weather, the shoots of turfgrass plants stop growing and the plants go dormant. Dormancy is a natural survival mechanism for turfgrass. While the leaves have turned brown and died, the turfgrass roots and crowns remain alive. Generally, Kentucky bluegrass can remain dormant for four to six weeks without suffering significant damage. Healthy lawns that have been allowed to go dormant will green up again when the turf receives enough water.
If deciding to water the lawn, apply 1 to 1 ½ inches of water per week in a single application or two applications three or four days apart. Avoid frequent, light applications of water which promote shallow rooting and lush growth. Lush, shallow-rooted turfgrass is less drought tolerant. It is also more susceptible to pest problems. To determine the amount of water applied by a sprinkler, place two or three rain gauges within the spray pattern.
When irrigating with a sprinkler, early morning (6-9 a.m.) is the best time to water gardens and lawns. A morning application allows the water to soak deeply into the soil with little water lost to evaporation. When watering is completed, the plant foliage dries quickly. Watering at midday is less efficient because of rapid evaporation and strong winds may cause uneven water distribution. Strong midday winds may also carry water onto driveways or streets, wasting considerable amounts of water. Watering lawns and gardens with a sprinkler in the evening or at night may increase disease problems.
In vegetable and flower gardens, drip irrigation systems and soaker hoses are more efficient and cause fewer disease problems than sprinklers. Mornings and evenings are excellent times to water gardens when using a drip irrigation system or soaker hoses.