Protecting the Health of Annex Trees

Many of the trees in Toronto are being hurt by urban development, the expansion of city infrastructure and our day-to-day activities. Some of these threats include:

  • Chemical stress (over-fertilization or contamination from de-icing salt)
  • Environmental stress (drought, too little sunlight, poor soil quality)
  • Mechanical stress (damage from lawn equipment, improper pruning practices, trunk wounds and severed roots from construction)

Most of the trees in the Annex - about 76% of them - are growing on private property. While trees are a source of enjoyment, many homeowners don’t realize that trees require monitoring and maintenance to keep them healthy.

How to Avoid Stressing Our Annex Trees

  • Water trees during periods of extended drought. Saplings should be watered consistently for three years after planting to ensure the tree’s success. Trees do best with infrequent and deep waterings (like a downpour).
  • Apply mulch under the tree drip line to conserve soil moisture, control soil temperature, and provide nutrients. (The drip line is the outermost circumference of the tree’s crown.) Avoid piling mulch against the trunk as it can lead to insect infestation, mold, decay and eventual death of the tree.
  • Do not over-fertilize your lawn. Too much fertilizer or the wrong kind of fertilizer can burn tree roots.
  • Do not store equipment or building materials under the tree drip line. This compacts the soil, which can reduce oxygen availability for the tree roots, and cause suffocation and death.
  • Ornamental rocks placed around a tree trunk also compact the soil.
  • Do not dig trenches or cut roots under a tree’s drip line. This can cause irreversible damage to the tree.
  • Prune trees only when it is necessary for structure, health, and safety purposes. It’s usually
  • best to consult a certified arborist for this.
  • Use proper pruning techniques, and never remove more than one-third of a tree’s branches within the same year. Look at the International Society of Aboriculture website for proper pruning techniques.
  • Do not "top" a tree. Topping is a harmful form of pruning, where large branches or whole trunks are removed from the tops of trees to reduce its size. Topping causes the tree to lose nutrients and become vulnerable to sunburn, insects and decay.
  • Be sure to remove vines, turf or competing vegetation from around the tree’s trunk.
  • When planting a tree, make sure the root flare is not buried. The root flare is the base of the trunk where it flares out slightly to meet the root system. Ensure that the base of the root flare is level with the soil surface.
  • Looking after a tree requires pruning, treatment for pests, and occasionally even tree removal. It is usually best to hire a certified arborist to resolve issues you cannot deal with yourself. 

The Emerald Ash Borer

Of the more than 10,000 trees in the TreesPlease inventory of Annex trees in 2010, 263 or 3% belong to ash species. They are currently threatened by the emerald ash borer that is spreading throughout the city. It is estimated that the epidemic will kill nearly all the ash trees in Toronto in the next 5 years.

What is the Emerald Ash Borer?

The emerald ash borer is an invasive insect from Asia that inhabits and feeds on all species of ash. Emerald ash borers kill ash trees by tunneling and feeding underneath their bark, disrupting the flow of nutrients and water within the tree. Infected trees usually die within 2-3 years. The City of Toronto has been removing dead ash trees from city streets and parks, and injecting healthier trees to prevent infestation. But ash trees on private property do not fall under city jurisdiction, and the financial responsibility for treatment or removal of such trees lies with the home owner.

Do You Have an Ash Tree in Your Yard?

Here are some tips on how to identify ash trees in your backyard:

1. Bark – mature trees will have tight diamond-shaped ridge patterns.


2. Leaves – they contain 5 to 11 leaflets with smooth or toothed margins that are arranged opposite to each other.

3. Seeds – the seeds hang in clusters, are smooth, and oar-shaped.

4. Branches – they are arranged opposite to each other.

Signs of Infestation by Emerald Ash Borer

  • thinning or yellowing leaves
  • vertical cracks along the bark
  • tunneling under the bark
  • D-shaped holes in the trunk where the emerald ash borer has exited, about 3.5-4 mm across
  • dead branches and crowns
  • tree death