Please Define Deep Watering

Q. Please define "deep watering." In particular, how would you describe "deep watering" a pomegranate bush with a 3" to 4" trunk?

A. Good question. I throw these terms around and I assume people know them or understand them when they don't.

            Deep watering is talking about applying enough water in one irrigation so that the entire root system becomes wet. When deep watering it is also accompanied by less frequent irrigations. This means giving the soil and roots a chance to dry somewhat before the next irrigation.

            There are two ways to water. One way is to give a small amount very often, perhaps daily or twice a day.

            The other way is to apply a large amount and then wait a long time before you give it more. The second way is preferable to the first way for plants that are deep-rooted. Deep-rooted plants are larger, woody plants such as all trees, all large and medium-sized shrubs, all woody vines, and all woody groundcovers.

            Water these types of plants deeply by applying enough water so that the applied water drains to a depth of 18 to 36 inches. The water is then shut off until that soil begins drying. Technically, the plant is not watered again until about half of the water in the soil has been used.

            When half the water is gone, water is applied again until it reaches the same depth as before. This is a continual cycle with the number of days between irrigations decreasing as it gets harder and increasing as it gets colder.

            Deep watering normally applies to woody plants but not to lawns, flowerbeds, vegetable beds and small fruits like strawberries. These are shallow rooted plants and their applied irrigation water is shallow, not deep.

 Deep watering a pomegranate that has a 1 inch diameter trunk is really no different than deep watering a pomegranate with a 3 to 4 inch trunk. Water is applied to the same depth with both of these trees. 

The difference between them is where the water is applied and the amount. In the case of a pomegranate with a 1 inch diameter trunk, we might use only two drip emitters. Two drip emitters might deliver enough water to the soil under the canopy while it is small. 

However, when the pomegranate gets to 3 to 4 inches in diameter, more emitters are needed because the larger tree requires more water. These emitters are spaced far enough apart so that the water is applied over a greater area under the canopy of the tree. The number of minutes on the irrigation clock may not of changed but the number of emitters has so the larger tree now gets more water.