We’ve recently installed an underground sprinkler system to water our lawn and perennial gardens, both of which have very sandy soil. Will the lawn and the garden beds have the same watering requirements? Also, how often should we run the sprinklers and what’s the best time to water?
Valerie Woodworth, Troy, MI
Howard Hendrix, co-author of Reliable Rain (The Taunton Press, 1998) replies: Lawns and perennial beds usually have different watering needs, especially at different times of the year. Many perennials have deeper root systems than lawns do, and are much more drought-tolerant. Conversely, other perennials demand constantly moist soil conditions to thrive. Therefore, it’s best to place your perennial beds on a different irrigation station than your lawn areas.
The two factors that will most affect the efficiency of your watering regime are heat and wind. As a good rule of thumb, don’t water between 10 a.m. and 4 p.m. That way you’ll avoid losing excessive amounts of water to evaporation during the heat of the day. Early morning is the best time to water, especially if your plants are prone to fungal diseases like powdery mildew.
If your area experiences regular early-evening winds, you might want to avoid watering then, too. Watering in windy conditions increases water loss through lofting, by which water droplets are literally blown away.
In the hottest climates and the driest summers, we recommend deep watering three to four times a week. That means watering until the soil is thoroughly saturated—as long as half an hour for most irrigation systems. In climates not so hot or dry, one can water proportionally less. Many factors such as soil type, the kind of irrigation system you have, and the drought-tolerance of your plantings will influence how often you’ll need to water. Remember, sandy soil usually does not retain water as well as clay soil. Both of these soil types will benefit from the addition of organic matter to improve soil structure and preserve moisture.
The bottom line with irrigation is simple: pay attention to what your landscape is telling you. Watch for signs. If your plants are wilting and getting crispy, they probably are suffering from a lack of moisture. If they look wilty and are yellowish, they may be getting too much water. Irrigation systems are handy robots, but both the irrigation system and the landscape will benefit from the presence of a responsive feedback device—a gardener—interacting with the two.