AMES, Iowa — Knowing when to water and how to water plants is one of the most important aspects of gardening and can make all the difference to the health of plants. Iowa State University Extension and Outreach specialists answer questions about watering plants in containers, gardens and lawns. To have additional questions answered, contact the experts at firstname.lastname@example.org or call 515-294-3108.
The frequency of watering may vary considerably from container to container. Watering frequency depends on the size and type of container, composition of the potting mix, plant species and weather conditions.
Plants growing in containers should be checked daily (especially in summer) to determine if they need to be watered. If uncertain about the need to water, poke your finger into the potting soil. Water the container when the potting soil at the 1 to 2 inch depth is dry. Watering frequency may vary from once or twice a day (small container, hot windy weather) to once or twice a week (large container, cool 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 soil to dry out completely. Potting soils shrink and pull away from the sides of the containers when completely dry. Dry potting soils are difficult to moisten as water tends to flow between the potting soil and container and then out the bottom of the container (while the potting soil 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 soil.
Most flowers, vegetables and fruits perform best when they receive 1 to 1½ inches of water per week (either from rain or irrigation). A deep watering once a week should be adequate for fruit, vegetable and flower gardens in dry weather.
Modern roses, such as hybrid teas, floribundas and grandifloras, require watering during hot, dry weather. The frequency depends upon weather conditions and soil type. In most gardens, a thorough watering every seven to 10 days during dry weather is sufficient. If possible, apply the water directly to the soil around each plant. Overhead watering wets the foliage and increases disease problems. If overhead watering is unavoidable, morning is the best time to water roses. Morning applications allow the foliage to dry quickly.
Most lawns in Iowa require 1 to 1½ inches of water per week. When watering the lawn, apply this amount in a single application or possibly 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 a.m. to 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 also may 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 fruit, 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.