Caring for City Street Trees

It’s not easy being a street tree in an urban environment. In New York City alone, 6,000 to 7,000 street trees die each year. When considering what a street tree has to endure—from drought and small growing spaces to infertile, compacted soil, it’s easy to see why the mortality rate is so high. But it doesn’t have to be this way. By giving street trees a little maintenance and care, you can help ensure that the 20,000 new street trees planted this year by MillionTreesNYC, the city’s forestry initiative, survive.

Trees add beauty to our neighborhoods and go a long way to enhance our quality of life. They improve air quality and reduce storm-water runoff, give us shade on sunny days, and provide wildlife habitat. Street trees are an essential part of keeping an urban environment happy and healthy. Here are some ways to care for your street trees.

Water

The area of exposed soil in a tree bed is relatively small, so even without a drought, a street tree can have a hard time receiving and retaining all the water it needs. Newly planted trees require 10 to 15 gallons of water a week. Mature trees do best when receiving 8 to 10 gallons of water a week. Be sure to water slowly so the moisture sinks in and doesn’t simply run off into the street. Set a hose to trickle water into the bed for an hour; or prick a few holes on one side of a clean garbage can, set it next to the tree bed, and fill it with your tree’s water allotment.

Mulch

A layer of mulch helps conserve moisture, and one made from natural materials will break down over time, adding nutrients to the soil. Choices include compost, wood chips, shredded leaves, or commercial organic mulches made from nutshells or other agricultural by-products. Covering the bed with brick or stone pavers is a bad idea; even loosely placed, they will prevent a significant amount of rainwater from being absorbed.

Plant the Tree Bed

Tree beds offer precious garden space to urban dwellers, and planting flowers or groundcovers with shallow root systems conserves moisture and adds beauty to the bed, with the added bonus of reminding pet walkers and other pedestrians that this is valued ground. Avoid large shrubs and water-hungry plants that will compete with the tree. Instead, try planting spring bulbs like snowdrops, crocuses, and miniature daffodils (which are shunned by squirrels rooting for food). After they fade, small annuals with shallow roots like zinnias and impatiens, or perennial groundcovers like bugleweed or stonecrop, will keep the bed attractive.

When planting or adding organic amendments to the bed, use a hand cultivator to gently loosen the soil to a depth of one to two inches without damaging tree roots, which are often quite close to the surface. Remove older soil if needed to accommodate your plants’ roots.

Don’t Smother Your Tree!

Raising the level of the soil above a tree’s base can actually kill the tree. Roots need oxygen, which they get from air trapped in soil. When too much soil is piled up, the air is squeezed out. Soil or mulch mounded up against the base of the tree can also cause the bark to rot, providing an entry point for pests and diseases, and create a home for gnawing rodents.

Well-meaning urbanites who build impermeable tree guards more than a few inches high and fill the bed to the brim with soil or mulch imperil the tree’s long-term health. Fortunately, there are alternatives to stone-wall tree guards.

Install the Right Tree Guard

Guards help protect your tree from animals, foot traffic, and damage from cars and bicycles. Monitor the guard as the tree grows to make sure it never touches the tree, continues to let water flow into and out of the bed, and does not allow soil to build up above the base of the tree.

Airy wrought or cast iron tree guards are elegant and durable, but they can be expensive. Two less expensive options:

• Post and Chain

  Drill a hole through one end of each of four sturdy wooden stakes or lengths of pipe. Drive one stake or pipe in each corner of the tree bed, then loop rope or chain through them.

• Log Cabin

  Stack pieces of wood alternately as if making a small, three-sided log cabin (open side to the curb is best). Drill down through each corner, then drive a length of rebar through the holes and into the soil to stabilize the guard.

Become a Tree Steward

Many cities supplement their municipal workforce with citizen volunteers who care for the trees in their own communities, including these two programs in New York City.

• Citizen Pruners

  Provides professional training and a license from the Parks Department to care for public trees.

• Street Tree Stewardship Initiative

  Gives free training, tools, and authorization to work in tree beds. Stewards can adopt specific trees to care for or reach out to community gardens and block associations to train other citizens in street tree care.