Ornamental landscape trees such as Japanese maples, flowering cherry, dogwoods and magnolias, to name just a few, benefit from deep irrigation. More frequent, shallow watering can supplement deep watering in times of high heat, in dry climates or if the trees are known to be very shallowly rooted. According to Arizona State University, ornamental trees require deep watering once every seven to 28 days depending on the size, type and age of the tree, the ambient temperatures, climate and the consistency of the soil. Water should always soak the whole root zone starting several feet out from the trunk and extending several feet past the drip line, drenching the soil to a depth of at least 2 feet.
Sprinkler attachments for your hose can easily be adjusted to deliver water to the root zone without landing water on or near the trunk. They may need to be moved several times, if the tree is large, but are a flexible and low-cost tools. They are also portable around the yard.
Fixed Line Drip Emitters
A piped irrigation system of fixed slow-drip emitters can be established to irrigate your ornamental trees. Most systems will accept additional lines making it easy to add more emitter valves out near the drip line of growing trees every few years as needed. The emitter heads can clog with mineral deposits and need to be checked periodically but after set up the system can be placed on a timer and operate on its own.
Soaker hoses that slowly ooze water from their pores over time are another flexible and low-cost solution as they can be moved around the yard from tree to tree and used in beds and borders. They function much like a drip emitter system, as far as the tree knows, but are entirely portable.
Flood irrigation is basic hose or container watering used best on relatively level grades. Berms or watering moats made of soil can also be created a foot or more out from the trunk and again around the drip line of the tree to create a doughnut-shaped basin to capture water and focus it into the root zone. You can fill the basin with a hose or watering can with 3 to 4 inches of water and allow it to percolate down into the root zone at is own pace. This is a low-tech, low-cost but very effective way to keep ornamental trees well hydrated and the trunks protected from root rot.