Keeping your trees healthy in the summer months

Jul. 12, 2014 @ 12:05 PM

Working outside in the heat can be a hard thing to contemplate from the comfort of our climate-controlled spaces.  However, as temperatures climb and the grass turns crisp, there is a lot to do, despite the heat, and the work that is most critical right now is watering and irrigation.
Drought stress can kill young or newly established plants, and it can stress mature or established plants to the point where they become vulnerable to other pests or pathogens. Signs of water stress include drooping branches, curling or shedding leaves and premature fruit drop. On mature trees symptoms can include shedding branches and “fluxing,” a condition where brown fluid seeps out of old wound areas, causing discoloration and sometimes a sour smell.  
From the grass in your lawn to the trees over the street, all plants need water. Their needs vary to a large degree based upon what the plant is and where it is located.
The varying water needs of plants can make for a challenging season of watering unless care is taken to group plants with similar needs together into beds or clusters.  Plants with an origin in the hot and dry Mediterranean or moist well-drained mountains can tolerate dry spells of varying intensity, but not prolonged wet conditions. This past year we lost a lot of trees, shrubs and plants due to the ground staying too wet for too long.  
Clay soils are a challenge to grow things in because they tend to hold water and stay damp, but it takes a long time for water to actually penetrate and move through them. Pair that with some variability in topography, and you have areas that stay wet and others that mostly stay dry. The next factor is the site’s exposure to the sun and to competition from other plants and trees. Mature trees can out-compete smaller trees, shrubs and ground-covers for available moisture.
Watering is best done in the early evening through morning. The best time is based on the plant (turf has its own set of watering best practices), but watering in the heat of the afternoon is not recommended.
This may all sound daunting, but it shouldn’t be.  We are currently not under watering restrictions, and some judicious use of mulch, soaker hose and other slow-release devices can increase the efficiency of your watering efforts dramatically. 
Mulch is your tree’s best friend right now because it keeps ground temperatures from getting too high. It also helps keep weeds down (and string trimmers away from delicate bark) while increasing the organic content of the soil at the base of the tree.  This is important because by increasing organic matter content in clay soils, you improve the soil’s texture and ability to take up water and facilitate root expansion.  But be sure to follow the 3-3-3 rule with mulch; 3 inches deep (maximum), 3-foot radius (minimum), with a 3-inch gap between the mulch and the base of the tree. No mulch “volcanos” please. 
The best mulch is organic in origin, aged and partially composted. Chips from freshly cut trees will lock up the nitrogen in the surrounding soil, creating an imbalance. It is also important to be sure that mulched trees are watered deeply.
If you have sponsored a City tree near your home or business, please water it now. Apply water at least once a week until fall. If you would like to use a tree “gator,” a limited supply is available for loan from Keep Durham Beautiful. 
If your sponsored City tree (or any tree you’ve come across on City property) has suffered from string trimmer damage and you’d like a guard placed at the base to protect it from further injury, you can request one to be installed by contacting Durham One Call (919) 560-1200.
Finally, if you’d like more specific information and/or tips on wateringvisit http://www.wemakedirtlookgood.com/watering-your-new-trees-and-shrubs/.
Alex Johnson is urban forestry manager, City of Durham General Services Department