No plant species is more dramatic, and useful, in the urban landscape than specimen trees. However, from an irrigation standpoint, they are largely neglected, and end up either over watered or stressed from lack of adequate moisture. Disease and pest infestation can also result, causing premature death. Large, boxed trees, whether nursery grown or transplanted, need careful management after installation if they are expected to survive during the first year.

Managing the irrigation of urban trees is not difficult or time consuming. A simple and inexpensive way to manage is to employ a few moisture sensors in various "indicator" trees located at a given site. This technique is rapidly emerging as a low cost "insurance policy" to avoid much more costly problems of mismanagement. IRROMETER (tensiometer) and WATERMARK (granular matrix sensor) soil moisture indicators have become very popular choices of both the arborist and the irrigation management profession. These instruments can be installed in the root ball of the trees upon planting, or easily added to existing treescapes to begin a management program. Very early in their initial use, they quickly indicate how well, or poorly, the soil water environment is behaving. And they often diagnose the lack of, and need for, proper drainage (a cornerstone of irrigation technology). They make possible a course of preemptive action, which can save literally thousands of dollars worth of damage later on.

Because a tree can explore a rather large area of soil with its root system, the management of soil water in this larger "reservoir" is critical to its initial healthy establishment and long term survival. Using IRROMETERS or WATERMARKS installed in this large "reservoir" of soil (usually at the 12"/18" or 31-45 cm. shallower horizon and 24"/36" or 60-90 cm. deeper horizon) provides the manager with a true "window to soil moisture" and directs the scheduling of irrigation as needed by the tree. These instruments, often called "dummy roots", clearly show what the root system is experiencing in its quest for water.

Experience shows that the properly established tree plantings do not require re-wetting of the soil water reservoir as often as is frequently practiced. And this frequent watering can result in a very shallow root system, an environment where the roots are starving from lack of aeration (anaerobic conditions), and a good breeding ground for disease.

At the onset, trees need careful management, and this means that the instrument readings need to be taken more often (maybe once per week). Once established, readings taken every few weeks are all that is required. Irrigation is initiated only when the need arises. The instruments report the "reading" in centibars (kilopascals) or soil water suction (a physical property of soil water, which indicates how hard the root system must work to extract water). Readings below 15 centibars (or kilopascals) indicate that the soil is more than adequately wet. Continued readings at 15, or lower, clearly show over watering or lack of drainage. As the soil dries down, readings begin to move higher. When the readings reach the 50 centibar (kilopascal) area - or when the rate of increase is very rapid - it's time to prepare to rewet the soil water area with an irrigation cycle. In some climates, such as Southern California, this may occur very infrequently in a year's time especially if winter rains have been normal or better than normal. In very dry winters, you may see the need to irrigate early in the spring or even late winter.

The small amount of time and money invested in IRROMETERs or WATERMARKs can pay big dividends in healthy and long-lived trees. Why leave the process up to "guesswork"? Measure the moisture and protect your investment.