Planting around a street tree

Street trees will probably do OK with flowers planted around them, as long as the tree roots are protected during planting and the new plants don't out-compete the feeder roots of the tree for water, soil oxygen, and nutrients. Some plants to be avoided because of their dense root systems include ferns, hosta, day lilies and grasses.

As you plant your flowers in the root zone of a tree, take some precautions to protect the tree roots. Roots larger than about an inch diameter help stabilize a tree. Take care not to damage or cut these; instead carefully plant around them.  

You may find a dense network of fine feeder roots in the area where you want to plant. These tiny roots are the ones that take up nutrients and water from the soil. This function is vitally important to the tree, so it is important not to remove any more than is necessary to make space for each flowering plant.  

If you find feeder roots obstructing the hole you're digging for a new plant, be sure to trim them back cleanly rather than tear them out. Clean cuts are easier for the tree to recover from quickly, which helps minimize the possibility of fungus infection. Water the area thoroughly, both right after you've planted your flowers and anytime the root area seems dry. Good for the flowers AND the tree!

When is the best time to prune a tree?

Removal of dying, diseased, broken, rubbing, or dead limbs can be done anytime during the year. Removing dead and damaged tissue can help limit further damage.  

However live-branch pruning is best done when the tree is dormant, in the winter or before growth resumes in early spring. Growth is maximized, and defects are easier to see. Pruning when trees are dormant can minimize the risk of attack from parasites and diseases associated with wounding and allow trees to take advantage of the full growing season to close and compartmentalize wounds.    Dormant pruning is especially important for elms and oaks.

Avoid pruning trees during or soon after flowers and leaves appear in the spring. This is when the cambium is active and bark is particularly vulnerable to being torn loose. Avoid pruning in summer too, when trees are still in active growth and may be stressed by drought. This is especially true for a tree that is already stressed by a limited root area or poor quality soil.

Another important consideration is nesting birds! The majority of songbird nests are small and camouflaged. Tree trimmers may not see nests until too late. Also, loud activity of tree trimming can disturb birds in surrounding trees.

Birds and active nests are protected from harm or harassment by the Migratory Bird Treaty Act. The Audubon Society advises that if you see tree trimmers disturbing an active nest, TAKE A PICTURE of the nest, the destruction, and the company's name. Report violations to the Law Enforcement Office of U.S. Fish & Wildlife Service at (310) 328-1516  (Office of Investigations and Compliance Inspection). The U.S. Fish and Wildlife Service will issue citations and may levy fines to individuals and companies that blatantly disregard the regulations.

Five easy things you can do to help care for our street trees all year long.

• Finger-prune new trunk sprouts when you see them

  Trees sometimes send out new leafy growth directly from the trunk. These sprouts take energy from the tree that the tree instead could be investing in healthy top growth. If the sprouts are allowed to grow they will eventually get in pedestrians' way and may be torn off, rather than cleanly removed.  Torn breaks are routes for infection into a tree.

  Trunk sprouts can easily be removed by hand while they are still young and tender. The older they are, the more difficult they will be to remove cleanly without a sharp tool. So help a street tree by snapping off new trunk sprouts cleanly with your fingers when you see them.

• Pull up grass and weeds growing around a tree, and mulch the tree site

  Weed-whackers are one of the most common reasons for tree death. The string beating against a tree's trunk at high velocity crushes circulatory channels lying just beneath the bark. Young trees are most vulnerable, but even mature trees can eventually be killed. Keeping the area around a tree weed- and grass-free reduces the likelihood of a weed-whacker getting close enough to the tree to do damage. It also reduces competition for water and nutrients. 

  You probably know mulching is important for plant health, because it helps keep the soil moist and reduces weed competition. But did you know that piling too much mulch around a tree can actually kill the tree? 

  • Download this useful pamphlet on the best way to mulch a tree (pdf).

  • And here's a link to a great video from This Old House showing exactly how a mulch volcano kills a tree. Thank you to the Arlington Tree Committee for finding this link!

• Don't store heavy things on the planting strip (and don't park your car there!)

Did you know that tree roots need oxygen? Both water and oxygen uptake from the soil are vital for tree health.  Roots need a soil structure full of tiny holes containing both water and air in order to absorb those nutrients. Parking on the planting strip compresses the soil so that it can no longer hold water and air and kills the feeder roots, which live only in the top few inches of the soil. Same goes for leaving heavy construction materials on the planting strip.

• Water the street tree in front of your house when it's dry

Many people think a tree's roots go very deep. Structural roots, the roots that hold a tree secure in a windstorm, can extend a few feet down. But a tree's feeder roots, which is how the tree absorbs nutrients from the soil, are only in the top few inches of soil, and can extend far from the trunk. If the soil around a tree dries out, so do the feeder roots.Young trees need regular thorough watering to establish good root systems.

Mature street trees too will benefit from regular thorough watering in a drought. The soil around them is often partially covered by hardscape or is of poor quality for holding water. If you want to help a mature tree in a drought, water its full root area thoroughly, once a week, at least as far out as the farthest branches extend.

Download a copy of the Tree Warden's guidelines for tree planting care (pdf) from the Tree Warden's website

• Let the Tree Warden know ASAP if you see a damaged or dead street tree

• Please contact the Tree Warden ASAP if you see damage to a street tree!  Prompt first aid by a knowledgeable arborist will minimize the routes for infection and help prolong the life of the tree. And a very badly damaged tree may be a hazard to public safety.  

• If you see street tree damage in process, please call the Tree Warden AND the Watertown Police. This is destruction of public property, and the perpetrator must recompense the Town. In the case of car impact, the car owner's auto insurance will pay for the damage, but only if the police can file a report identifying the driver. Recompense for destruction of a public shade tree is calculated using a formula based on the diameter of the tree. 

• Street and sidewalk renovation is hard on street trees.  Watertown's contracts include procedures for tree protection, but sometimes those procedures are not  followed. Please contact the Tree Warden as soon as you see tree problems at a street renovation, so that he can remediate the damage and make sure contractors understand their responsibilities to protect Watertown's street trees.  

• Please immediately report a dead tree to the Tree Warden. Quick notification can save the town money, and the sooner a dead tree is removed, the sooner a healthy new tree can be planted in the same site. 

When a branch is broken or bark is damaged, a tree will try to heal itself, but if the damage is left untended, good healing may be impossible. Much as bacteria will find entry into our body via a dirty cut, insects and fungi will use a jagged wound to infect a tree. Energy a tree must put into isolating the wounded part is energy it can't spend on healthy growth.

Torn or dried-out roots can also cause serious injury to a tree, by limiting its ability to absorb soil nutrients or as an entrance point for infection. Until professional help comes, it can be helpful to cover exposed and damaged roots with wet burlap or another moist covering (make sure it stays wet). Unfortunately for our trees, if reburied without first aid, root damage can continue to degrade the health of a tree. The damage is insidious: it can take years for a healthy mature tree to decline due to root damage. Commonly, at that point the cause of the decline is long forgotten and there may be little that can be done to help the tree recover.