Issue 68
September 14, 2006

Weather Trivia

 You Asked Us

Environment Canada's knowledgeable specialists answer questions about wildlife, air pollution, water, weather, climate change and other aspects of the environment.

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Can I plant a tree in fall? How do I prepare the young trees in my yard for winter?

Planting trees is one way to help improve the environment. Trees clean the air by taking in carbon dioxide, storing carbon, giving off oxygen and recycling moisture into the atmosphere. They also help prevent soil erosion, modify temperatures and light, act as windbreaks and provide food and shelter for birds and other wildlife.

Although there are some general guidelines to planting trees, your best bet is to consult an expert at your local greenhouse or nursery – they will have specific expertise on planting certain species in your region.

When to Plant

Deciduous trees – those that seasonally shed their leaves – can be planted in the spring, as soon as the frost is out of the ground, or in the fall, from leaf-fall until freeze-up.

Conifers, or evergreens, can be planted early in the spring until four weeks after deciduous trees have opened their leaves. They can also be planted in the fall, from about the first week of August to the end of October.

Planting trees in fall can be risky if the following winter turns out to be particularly severe. Certain species, like poplars, willows, ash, elms and birches tend to overwinter better if planted in the spring.

Where to Plant

Select trees that grow well in your local climate and soil. Each species has a different tolerance to late spring or early fall frosts, flooding or drying, high winds, low light levels and different soils. It is always best to plant species native to your region and to avoid introducing species that are considered invasive.

Think about what the tree will look like at maturity – very large trees can be overpowering on a small property. Do not plant trees close to overhead and underground utility lines or near underground piping.

Deciduous trees on the southeast, southwest and west will eventually provide cooling shade in summer without obstructing the low winter sun. An evergreen windbreak along the north side of a property blocks cold winter winds.

Winter Preparation Checklist

Winter is a stressful time for trees, even for species native to colder regions. Below-zero weather, storms, ice and rapid temperature fluctuations take their toll on trees, particularly on the young, exposed trees of residential landscapes. Some of this stress is unavoidable; however, there are some steps you can take to minimize the damage caused by winter stress.

• When adding new trees in the fall, purchase only those species native to your area's hardiness zone. Trees native to even slightly milder areas than yours might experience significant stress during your region's winters.
• Maintain good tree upkeep throughout the year. Strong healthy trees will always have an easier time than weak and damaged ones.
• If pruning in the fall, do so only after your trees have entered dormancy. Pruning too soon might encourage new growth and increase the risk of frost damage because late season tree growth is more vulnerable to cold stress.
• Branches are more vulnerable to breakage during the winter. Particularly for deciduous trees, the wood hardens and becomes more brittle and susceptible to wind damage. The weight of ice and snow accumulation affects both deciduous trees and evergreens. Very small trees may need to be entirely covered with a sturdy tent-like housing.
• Apply a good fall fertilizer that promotes root growth over leaf growth. Avoid using fertilizers with high amounts of nitrogen, which can reduce hardiness if applied too late in the growing season. When applying fertilizer, always ensure adequate availability of moisture for the uptake of nutrients.
• Spread a layer of mulch down around the bases of your trees to moderate temperature fluctuations and moisture loss. Winter drought, which can be a real problem for evergreens, occurs when a tree loses more water than it can absorb from the frozen ground. Windy conditions can worsen winter drought. Laying down a thick layer of organic mulch around the base of the tree in late fall can help to slow moisture loss and runoff while acting as a temperature buffer for the roots. Don't forget to leave a space between the mulch and the trunk of the tree to discourage mice.
• Check occasionally during the cold season for signs of rodent damage. During the winter, trees can become a target for rodents – mainly mice, rabbits and squirrels – foraging for scarce food.

Related Links:

• Green Side Up – A Guide to Tree Planting
• A Guide to Planting Trees for Urban Residents
• Native Plant Crossroads
• Tree Canada Foundation
• The Cold Facts About Winter – Nursery Fact Sheet