Tree roots are not like carrots. Tree root systems can spread 2 – 3 times wider than the height of the tree. Roots will grow where moisture and oxygen are available. As a result, most of the tree's fine absorbing roots are in the top 12 inches of the soil. Water should be applied within the dripline of the tree (the Critical Root Zone in the box to the right).
Water deeply and slowly. It's important to water slowly, so the water is able to completely infiltrate down to the tree's root system. Watering for short periods of time will only encourage shallow root development, which can actually lead to more severe drought damage. Apply water so it moistens the critical root zone to a depth of 12 inches.
Methods for watering include a soaker hose (preferred method), deep root fork, deep root needle or soft spray wand. Apply water to many locations under dripline. For evergreens, water 3' - 5' beyond the dripline on all sides of the tree. If a deep root fork or needle is used, insert the device no deeper than 8 inches into the soil.
Don't dig any holes around your tree in a effort to water deeply. This will tend to dry out the roots even more and may result in direct damage to the roots.
Organic mulch helps conserve soil moisture. A 2 - 4 inch layer of organic mulch reduces soil moisture loss from evaporation, moderates soil temperature extremes (hot and cold), reduces competition from grass & weeds, improves soil aeration & soil structure, adds organic material to the soil, and will help prevent lawnmower & weed whip damage to the trunk. Apply organic mulch within the dripline, to a depth of no more than 4 inches.
A layer of mulch deeper than 4 inches may cause problems with gas exchange. Leave a 3 - 4 inch space between the mulch and trunk of trees. If the mulch comes in contact with the tree trunk, decay causing fungi and insect pests may cause serious damage to the tree. Mulch materials may include wood chips, bark, leaves and evergreen needles.
Eliminate turf under trees prior to adding mulch. Use "glyphosate" herbicide taking care not to apply it to tree foliage including trunk sprouts. Ask your nursery professional for recommended brands.
Do not fertilize a tree that is under drought stress. Fertilizers contain salts that may burn the roots when there is not enough water in the soil. Also, fertilizers may stimulate excessive canopy growth with too much leaf area for a drought-stressed root system to maintain.
Moisture is needed to avoid disease and insect pests. Drought stressed trees are more vulnerable to disease, insect infestations, and branch dieback. Routinely monitor your trees throughout the growing season. If you notice anything that looks out of the ordinary, contact a licensed, certified arborist.