Trees need water to survive. Relying on natural rainfall does not necessarily provide sufficient water requirements to trees especially in the urban environment. Proper watering techniques are especially important for newly planted trees as many of their roots have been lost during digging and transplant process. Recovery from transplant shock, i.e. severe root loss, may take several years and is largely dependent on how efficiently the tree is receiving water to promote new root growth.
Trees require infrequent deep watering as opposed to the frequent shallow watering which typically done with shrubs and perennials. Providing less frequent, saturating watering encourages deeper root growth which promotes increased drought tolerance.
Unless you already have in-ground irrigation, slow drip irrigation is the best method to achieve deep watering. The use of a watering bag or a soaker hose are examples of effective watering methods for young trees. Both devices are designed allow the water to drain very slowly, drip by drip. And as each drip is released it percolates deeper into the soil without oversaturating the soil and making it soggy.
Water bags have a capacity of 15 gallons and can take 5 to 8 hours to empty through two small emitters under the bag.
Upright slow release watering bag. Unzipped water bag. For large diameter trees 2 bags
can be zipped together
Horizontal slow release watering bag.
Soaker hoses are laid under the drip line of the tree and can be left there all season. These hoses can also be buried lightly under the soil surface. One end of the soak hose is capped while the other connects to the garden hose. The hose can be left running for 2 hours with only a half turn of the water valve. With soaker hoses the water essentially sweats and beads out from the hose. Do not confuse soaker hoses with the hoses with perforated holes which spurt out thin sprays of water.
Soaker hose laid under drip line of tree.
Newly planted trees should be watered a least once a week during the growing season until late fall. Adjustments can be made accordingly during rainy periods (skip a week) or dry spells (water twice a week).
Avoid overwatering. Too much water can oversaturate the soil and promote root rot diseases. Because roots require oxygen to survive, overwatering can displace the air with water and potentially suffocate the roots. If water begins to pool on top of the soil surface, stop watering and allow the water to drain into the soil. Water drainage is slower with compacted soils and clay soils.
One last tip, don’t water directly at the trunk of the tree or at the base of the trunk. These areas do not absorb water. Water uptake is done by the fine feeder roots that grow further out from the trunk.