Trees grow a little differently than other plants in our landscape plants due to their size and lifespan. To keep them healthy, we need to keep their specific needs in mind but also remember that their root system allows them to access some water and nutrients that may not be available to shallow-rooted plants like grass and flowers.
Water needs
Mature trees rarely need additional water. They are typically able to withstand short periods of drought, although trees that have already been stressed by disease or being planted in the wrong place my succumb to additional stress by drought. If you have a tree that was already suffering, a little extra water my put off the inevitable, but it will not save a suffering tree forever. The typical recommendation for irrigating a home landscape is 2 inches of water per week. If that is supplied through rainfall, no additional irrigation is necessary. If you are already watering your lawn or garden and the tree root zone is in the path of the water, they are likely already receiving enough water. The key is to water no more than once a week and to water deeply at each application. Watering more often will cause disease. (Not sure how long it takes to apply two inches of water in your landscape? Place a rain gauge under your sprinkler and time it out!)
Young trees do need additional water. When you plant a new tree, be prepared to supply water at planting and weekly thereafter until dormancy. Planting deciduous trees in the fall and winter when they are dormant is one way to reduce water stress as trees take up less during this time. For more information on watering trees, read more here.
Fertilization
It’s impossible to know what a tree’s fertility needs are without a proper soil test. Contact your local Extension office to find out about having your soil testing. Fertilizers are primarily broadcast across the root zone. Fertilizer stakes are also available, but force the tree to come to one place to find nutrients. Broadcast slow-release fertilizers may be more effective at nurturing the entire root system. Fertilizer should be applied early in the spring as buds begin to appear. Fertilizing to late in the year can encourage trees to stay active instead of going dormant, exposing them to risk of frost damage. When you’re ready, read more about correct application in Care of Ornamental Plants in the Landscape.
Mulching
Mulching is a great way to conserve water, protect any surface roots, and reduce competition with other plants. Any organic material is appropriate, from pine needles to wood chips. Mulch should be applied 3 – 4 inches deep and can stretch all the way out to the edge of the canopy. Because grass will be unhappy in deep shade anyway, using mulch liberally around the base of the tree is an easy answer to the problem of trying to make grass grow under your tree.
First do no harm
Avoid injuring surface roots or the trunk of the tree with lawn care equipment. If surface roots are spreading through the yard, consider mulching the area. Pruning large surface roots is never a good idea, and repeated injury by equipment can introduce pests and disease. Hanging bird feeders, swings, or building large structures around trees can also cause injury. Avoid parking cars on top of tree roots as well.
Read more about Shade and Street Tree Care.