How Shifting Planting Zones in Toronto Are Changing Garden Choices

Over the past 20 years, Toronto has experienced significant changes in its climate, pushing its planting zones into warmer categories. This shift has had a profound impact on what plants thrive here and has opened up possibilities for new varieties that were once challenging or even impossible to grow. However, it also brings complications, as some native plants are now at risk of becoming invasive due to the shifting climate.

The Shifting Zones: Toronto’s Move from Zone 5 to Zone 6

Historically, Toronto fell into USDA hardiness zone 5. Over the last two decades, however, it has gradually warmed to a solid zone 6. The main reasons include:

• Warmer Winters: Winters are consistently milder, with fewer deep freezes.

  
  

• Extended Growing Seasons: The frost-free period has lengthened by several weeks, creating a longer growing season.

  
  

• Increased Summer Temperatures: Hotter summers push plants that favor cooler conditions out, while those that thrive in warmth are finding a foothold.

  
  

This transition to a warmer zone impacts every level of gardening and ecological planning, from the types of trees we plant to the ground cover we select. For urban gardens like those we create at Pollinator Gardens Canada, adapting to these changes is crucial to maintain sustainability and balance.

New Plant Options for Zone 6 Toronto

With the shift to zone 6, Toronto gardeners can now introduce plants that previously struggled to survive the colder winters. Here are a few examples:

1. Perennial Herbs

   Plants like rosemary and sage, traditionally suited to warmer climates, are now capable of overwintering in some sheltered areas. These hardy herbs can add fragrance and utility to a garden that could previously only sustain them as annuals.

   
   

2. New Ornamental Grasses

   Ornamental grasses such as Miscanthus and Pennisetum now thrive in Toronto’s zone 6. These add texture and movement, bringing additional ecological value as they provide habitat and food for native pollinators.

   
   

3. Broadleaf Evergreen Shrubs

   Broadleaf evergreens like Pieris japonica and certain cultivars of rhododendron are better suited to zone 6. These shrubs provide year-round greenery and support local pollinators with their early blooms.

   
   

4. Native and Non-Native Perennials for Pollinators

   Some perennials that previously only worked as annuals in Toronto, such as Asclepias incarnata (swamp milkweed) and Monarda didyma (bee balm), can now be reliably perennial. This change not only enhances garden beauty but also significantly supports pollinators like bees and butterflies.

Native Species Becoming Invasive?

A warming climate doesn’t just welcome new plants—it also disrupts existing ecosystems. Native species that thrived in Toronto’s cooler zone 5 conditions may now exhibit invasive behavior as they spread to warmer zones. This shift poses challenges, especially for ecological design:

1. Canada Goldenrod (Solidago canadensis)

   Canada goldenrod, a native wildflower, is known for its bright yellow flowers that attract pollinators. With warmer winters, it can now spread more aggressively and outcompete other plants, risking biodiversity in local ecosystems.

   
   

2. Virginia Creeper (Parthenocissus quinquefolia)

   Virginia creeper, a hardy native vine, has become increasingly invasive in warmer conditions. Its rapid growth can overwhelm nearby plants and reduce available resources, complicating efforts to create balanced native gardens.

   
   

3. Sumac (Rhus typhina)

   Sumac, known for its vivid fall color, is another native species benefiting from warmer zones. While it supports pollinators and birds, its aggressive growth can disrupt other native plants, particularly in managed landscapes where diversity is a goal.

   
   

4. Eastern Red Cedar (Juniperus virginiana)

   Eastern red cedar, once more confined to southern Ontario, is extending its range. In native ecosystems, its spread can hinder smaller plants and change soil conditions, reducing habitat variety.

Adapting to the Changes: Strategies for Sustainable Gardens

For sustainable garden design, recognizing these shifts means choosing plant species with care. At Pollinator Gardens Canada, we approach design with an eye toward supporting local ecosystems in the following ways:

• Opt for Adaptable Natives

  Certain native plants, such as Echinacea purpurea (purple coneflower) and Coreopsis verticillata (threadleaf coreopsis), are resilient to both cool and warmer climates and continue to support pollinators without the risk of invasiveness.

  
  

• Use Non-Invasive Cultivars

  Cultivars of traditional plants may provide the desired visual effect while limiting aggressive spread. For example, choosing compact forms of sumac can offer fall color without the same invasiveness risks.

  
  

• Plan for Layered Planting

  Integrating a variety of native and adapted plants at different heights helps balance resource competition and reduces the dominance of any one plant, supporting biodiversity.

Embracing Zone Shifts for a Resilient Future

As Toronto’s climate evolves, so must our gardens. This shift in planting zones offers an opportunity to be both creative and conscientious, adapting gardens to the changing environment while prioritizing biodiversity and ecological health. The challenges of managing invasive natives or incorporating new plants require thoughtful planning but can ultimately make urban landscapes more resilient and vibrant.