With the Governor of California declaring a drought emergency and some Bay Area communities already starting to institute water rationing, our trees may be in trouble.
Trees which depend on winter rains like our native oaks will likely be going into the summer months in a stressed state. In addition, if landscape trees are planted in
lawn areas and water restrictions limit the use of irrigation for lawns these trees will also be subject to stress.
Water is the single most important factor in the growth of trees. Reduced water will cause reduction in the growth of roots and foliage. Trees may have yellowing or browning of foliage and branch tips may die. In extreme conditions a tree may die. There are some things you can do now to help reduce the impacts of drought for both native and ornamental landscape trees.
First of all doing supplemental irrigation during the winter is beneficial to oak trees. Normally, providing irrigating oak trees is not advised but during a drought period irrigating the trees can help to reduce stress. The reason irrigating oaks is discouraged is because moist warm conditions favor the growth of root fungi that affect our native trees. Irrigating during the cool winter months is less of a risk to the development of root fungi. I recommend slow watering out to the drip line but
be sure to keep water at least three feet from the trunk of the tree where the root fungus are most likely to affect the tree's roots.
Another important step is to install arbor mulch around your trees. For landscape trees this may mean removing lawn from around trees. When lawn is removed and
the irrigation is discontinued drought stress can occur for the trees. Installing mulch to a depth of four inches out to the drip line can reduce drought stress. Periodic irrigation during the summer if possible is also advised. Deep watering for trees that have had sod removed every week or two is helpful to maintaining optimal tree health. Make sure to keep mulch a foot or two away from the trunks of trees to discourage root fungi.
Other benefits of applying mulch include better saturation or rain water, better water retention and moderating soil temperatures during the warm summer months. Mulch as it breaks down in the soil also adds humus and micro nutrients that help roots grow and provide additional nourishment to the tree.
Reducing competition from shrubs or ground cover below trees will also mean more water is available for your tree. Ivy is especially problematic for trees because it
takes water away from the tree and can also climb up into the tree and deprive the branches of light. Removing thirsty shrubs and ground cover and replacing them with drought tolerant choices will mean more water is available for your tree.
For more information on optimizing the health of your trees please view our articles section at treeprosonoma.com
Ron Wallace, Certified Arborist #WE 0979A