Healthy trees

Healthy trees, healthy communities

Trees are an important part of our daily lives. They are often called nature’s air conditioners as they provide shade and relief from the sun’s heat and harmful rays. They also absorb carbon dioxide (a greenhouse gas), and in turn, replenish the atmosphere with oxygen for us to breathe.

In addition, trees make our environment more beautiful with their different colours, flowers and shapes. They give us a sense of peace and invite us to relax. Trees give us a lot and ask for very little in return.

There are many benefits to trees and shrubs in your landscape. Trees and shrubs can help to:

  • Conserve energy;
  • Increase property value;
  • Reduce stormwater runoff;
  • Provide shade protection from the sun;
  • Provide habitat and food for wildlife;
  • Improve general aesthetics of your landscape;
  • Decrease summer time evaporation;
  • Increase groundwater recharge;
  • Reduce the need for noise abatement; and
  • Improve air quality.

What is a tree?

A tree is defined as a woody, perennial plant that grows to a height of at least 4.5 metres at maturity with a more or less definitely formed crown of foliage.

Conifers vs. deciduous

All trees in Canada can be distinguished as being a conifer or a deciduous tree.

Conifer trees:

  • often called evergreens, needle-leaved trees or softwoods
  • can lose their needles annually but most are evergreen
  • have needlelike or scalelike foliage and usually renew many leaves annually
  • foliage is usually narrow and sharp-pointed or small and scale-like
  • the seeds are grown in cones
  • three major groups – firs, spruces and pines that are identified by their needles
  • firs – short needles with blunt tips
  • spruces – four-sided needles that are sharp
  • pines – needles grow in bunches, wrapped together at the base

Deciduous trees:

  • often called broadleaf or hardwoods
  • have broad, flat leaves
  • are perennial plants that are leafless for some time during the year
  • most shed their leaves in autumn
  • seeds are protected inside a hard nut or fleshy fruit
  • include maples, oaks, willows, ash


Like all plants, a tree begins from a seed. A seed must have food, water and light to grow. Once the seed sprouts, it grows into a seedling that grows into a sapling and eventually saplings grow into trees that produce their own seeds.


All trees have roots, which have two important jobs to do. They anchor the tree to the ground so that it can stand upright, and they absorb water, minerals and nutrients from the soil.


The trunk of a tree, which is protected by a tough outer covering of bark, connects the roots to the branches and transports water and minerals from the soil to the rest of the tree. The trunk supports the tree and as it grows taller than the plants around it, it is able to reach more sunlight, which is essential for growth.

Branches, leaves and twigs

Branches connect the trunk to the leaves and transport water and minerals to the leaves. The leaves, which are held up by branches, are arranged in a way that captures maximum sunlight. The tips of branches are known as twigs and these are the growing ends of the tree. Leaves grow on the twigs and produce food for the whole tree, but can only do this in sunlight.

Photosynthesis (how the tree feeds itself)

Leaves use energy from the sun to convert carbon dioxide in the air and water from the soil into sugars to feed the tree. This process is known as photosynthesis. Trees release oxygen into the air during photosynthesis. This is very important, as all animals, including us humans need oxygen to survive.

Trees are an integral part of our environment and a valuable asset to our community. We must manage this resource in the best way possible to provide the future with a sustainable urban forest.

Visit TreeCanada to learn about more ways to help trees

Please share a drink with our trees

Guelph’s newly planted trees (less than three years old) can become distressed from the warm, dry weather we experience during the summer.

The City of Guelph urges residents to water any newly planted tree that is close to your home or place of business. Just 20 litres of water on a regular basis — that’s two pails or two minutes with a garden hose — will help preserve this natural resource.

Trees are precious. They clean our air and our water and make Guelph a great place to call home.

Guelph’s Outside Water Use Program doesn’t restrict tree, shrub, flower or garden watering during Level 0 Blue and Level 1 Yellow conditions, and allows for alternate day and time watering restrictions during Level 2 Red.

Common tree problems

Powdery Mildew

Fungi that grow superficially on the leaves causing a grayish fungus layer. Resulting from a lack of air circulation.

Black Knot

Black, rough cylindrical shaped galls. Treatment – prune knotted twigs and excise knots on large branches during winter.

Tar Spot/Black Spot

Irregular, shiny black tar-like discolourations that can be up to 1/2″ in size. Treatment – rake and compost leaves.

Leaf Hopper/Aphids

Small insects that suck and chew on a variety of trees (i.e. Locust) and give the appearance that sap is dripping from the tree. The insects feed for approximately 4-8 weeks, depending on weather conditions.


A sudden wilting or dying of leaves on individual limbs. Does not spread rapidly and lives in soil. Fertilization is the only recommended practice.


A drying up of the upper side of the exposed tree bark giving the tree a bleached appearance, causing slow decay.


Many different varieties. Majority of these growths live on decaying matter that can be found on either the tree or on the ground.

Girdling Roots

A growth habit of certain roots – circular in fashion, causing slow death of trees in urban environments.


Primarily caused by a variety of mites laying eggs on upper side of foliage.


A variety of fungal fruiting bodies that can cause structural problems as they grow.

Leaf Scorch

The leaves of many deciduous trees, particularly Maples, may be scorched on warm windy days, resulting in a discolouration of the leaf surface.