Georgetown’s cherished street trees bring inestimable beauty and grace to our historic village and are important because they clean the air (by removing carbon dioxide and particulates) and cool our neighborhood (thereby saving cooling costs). The trees also absorb rain and dissipate storm-water runoff, provide welcome shade, and are havens for birds and wildlife.
But city life is extremely hard on trees: they endure limited rooting areas, pollution and physical damage. A tree growing in parkland can live for hundreds of years and the average life span of a tree in the suburbs is 30-40 years. But that same tree, planted in the city between sidewalk and street, may only live for 15 years. This is why it is so important to give tender loving care to our new trees to enable them to live longer.
How you can help: The most important way to help street trees is to water them, protect them from dogs, pedestrians, cars and salt and give them plenty of room to breathe and grow.
Water is the single most important component of a young tree’s survival. Water twice a week, slowly and thoroughly, soaking the ground with 20-25 gallons of water a week. Continue watering, as needed, until the leaves drop off in the fall. Resume watering when new leaves appear in the spring. But do not over water: pull the mulch away and test the soil with your finger -- if it is wet, do not water. The best water for trees comes from rainfall that is light, but lasts several hours. The heavy rain experienced in summer thunderstorms is not particularly beneficial because it mostly runs off into storm drains.
Dog urine is very caustic to both the bark and roots and as it accumulates in a tree box, it will often kill a tree.
Pedestrian traffic over the soil will compact soil, making it impenetrable to water and air. When roots are starved of these crucial elements the trees become highly stressed and are often colonized by insect or disease pathogens.
Fencing helps trees by discouraging dogs and pedestrians. Fencing should be at least 18 inches high and installed on only three sides (no fencing is allowed on the curb side). Fencing should be minimal and not have an impermeable border at sidewalk level that would keep storm-water from entering the tree box. Railroad ties and brick borders are undesirable because they encourage the addition of excessive dirt which can kill newly transplanted trees.
Cars and trucks often damage trees by breaking limbs or wounding the tree’s bark.
Salts act to draw water out of the soils which keeps trees from absorbing water. Be careful when applying ice melting salts near our street trees.
Room to breathe and grow. Most of our beautifully planted tree boxes are actually harmful to their host trees. Digging in the tree box severs tree roots. Adding excessive dirt interferes with the absorption of air and water into the tree well and creates an environment for future rooting problems called “girdling roots.” All this creates stress and jeopardizes the development of the tree. Recent surveys within Georgetown also found that trees in boxes planted with annuals were over watered. This can lead to many problems including root rot that will eventually kill the tree.
Mulching to a depth of two to four inches will retain moisture for roots in the summer and keep them insulated during the winter. But don’t over-mulch. Adding more than four inches of mulch inhibits the flow of air and water to the roots. Two to four inches of mulch is good, but more than this leads to long-term problems. Also make sure your mulch is pulled away from the trunk by an inch or two – otherwise it traps moisture which leads to cracking and sloughing of the bark allowing fungus, insects and rodents to invade.
-- Betsy Emes, Chair, Trees for Georgetown and Keith Pitchford, Consulting Arborist
