Trees need water to survive. Water is used by trees to carry nutrients obtained from the soil throughout the tree. During periods of hot, dry weather there is often less moisture available in the soil. In response to the dryer soil, trees will slow their normal process of absorbing water through their roots and releasing it through their leaves in order to avoid 'drying out'. This built-in survival mechanism allows trees to deal with hot, dry weather, but this cannot be sustained for extended periods of time.

Trees that are most susceptible to the effects of hot, dry weather are newly planted trees and those which are already under stress. Recognizing this, the City routinely installs moisture retaining mulch around trees when they are planted. During periods of drought the City regularly waters trees which have been planted in the last few years and those growing in sidewalks surrounded by hard surfaces with limited access to water.

Maintaining Newly Planted Trees While Conserving Water

For the first 2 to 3 years after a tree is planted, the area around the base of the tree should be kept moist at all times. During a drought, when it is important to conserve water, you should use every available method to ensure this area doesn't dry out.

1. If you have a rain barrel, connect a garden hose to it and use it to water your tree, as long as water is available. If small children are using a splash pool to stay cool, you can reuse use the water from it to water your tree. The water collected by a dehumidifier is another excellent source of water for your tree.
   
   
2. Maintain mulch around the base of the tree. Doing so will help keep the soil moist. Be sure not to pile mulch against the trunk of the tree as this can cause the bark to decay. This can also lead to insect and disease problems. Keep mulch 15 cm from the base of the tree. 
   
   
3. Direct water to the perimeter of the mulched area of the tree. When newly planted trees, like the one shown here are dug up at the nursery, they lose as much as 95% of their root system.  After planting, the tree spends the next 2 to 3 years recovering and growing new roots while establishing itself to its new environment.  That's why it's important to keep the perimeter edge of the planting area moist in order to encourage root growth outward from the tree rather than up into the surrounding mulch.
   
   
4. The amount of water needed will vary depending on the type of soil that exists, where the tree is planted and weather conditions. For this reason, it is best to keep the dashed area, shown in blue moist. Do not let it dry out!

Trees are precious. They clean our air and our water and make Toronto a better place to live. Help keep our urban forest growing.

• Trees Need Water (PDF)