Ask the Expert

Keeping trees healthy

Q: We just moved in to our new house and have several beautiful mature trees on our property. They look like they can fend for themselves, but are there any special tips for keeping them healthy and in tip-top shape?

Mature trees and shrubs are often the focal point of a landscape and their value can be measured in many different ways. Trees provide shade, beauty, spring and fall color, wildlife habitat and can help moderate temperatures within a home. Mature trees, however, can also be hazards, and their structural integrity and overall health should be evaluated by a professional periodically. I highly suggest making an appointment with an ISA Certified Arborist from a reputable local tree service to walk the property with you and provide information and help develop a comprehensive, long-term management plan for the landscape. Most tree services are happy to give free estimates and the information they provide can be immensely helpful for a new homeowner. Arborists help identify plant species, evaluate trees for any structural defects, determine pest or pathogen presence, and make recommendations on which trees should stay or be removed to create the desired landscape.

My No. 1 recommendation to homeowners who wish to maintain good health of their trees is to provide sufficient watering. Even in Southcentral Alaska, where it rains frequently, much of the time the rain falls in a low volume and is absorbed by turf or evaporates before reaching the deeper roots of the woody plants. Ample watering in the evening is perhaps the most important action homeowners can take to provide for long-term health of all plants in the landscape.

My second recommendation is to avoid physical damage of any kind. This often occurs as a result of contacting the main stem near the base of a tree with lawnmowers and string trimmers. The wound created can become a point of entry for pest and disease, will disrupt the ability of the tree to uptake water into the upper canopy and can eventually become a cavity, making the tree more likely to fail. Installing mulch rings near the base of trees is an attractive and effective solution to this problem and has the added benefit of feeding the soil near the plant and reducing the likelihood of soil compaction.

Fertilization is often unnecessary and can sometimes have negative impacts on trees and shrubs. Over fertilizing is common and can burn plants, and large increases in nitrogen can lead to greater defoliating pests (ie, aphids and leaf miners), which damage trees by eating leaves or needles. Avoid fertilization until it has been determined that the soil is deficient in one or more nutrients and that any pest population is controlled.
In summary, the best thing a homeowner can do to care for mature trees and shrubs is to simply maintain good growing conditions. Trees and shrubs are remarkably engineered organisms and their ability to cope with stress and adapt to changing conditions is extraordinary. Looking after your trees is easier than you may think and will provide benefits for years and decades to come.

Greg Matthews has a B.S. in Urban Forestry and has worked as a Climber and Arborist for 12 years. He is currently the General Manager of Tall Trees Inc., a tree service located in Anchorage.