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Gardening in Zone 4

Are you interested in why some plants grow in certain areas but not others? Or maybe you are familiar with plant hardiness zone numbers but not quite sure what this means for you in your own garden?

Gardening in Sudbury, Ontario

Living in the City of Greater Sudbury in northern Ontario, we are in what is called plant hardiness zone 4. This is further divided into zones 4a and 4b depending where you are located in Sudbury. View all hardiness zones here from the Natural Resources Canada website.

Hardiness Zones

Hardiness zone calculations come from several climate data variables including averages of:

  • Coldest minimum temperatures in winter
  • Number of frost-free days
  • Rainfall patterns
  • Warmest maximum temperatures in summer
  • Snow depth
  • Wind gusts, and more…

These averages are calculated using a formula to produce the hardiness index. This index is then turned into a visual map showing each zone across Canada. Below is a screenshot of the hardiness zones across Ontario:

Plant Hardiness Zone Map from Natural Resources Canada zoomed into Ontario
Ontario Plant Hardiness Zone Map from Natural Resources Canada

If you travel south to Toronto or Niagara, you will find the hardiness zone has changed to a higher number (up to zone 7). If you travel north to Timmins or Moosonee, the number gets lower (down to 1 or 0 along James Bay and Hudson Bay). Therefore, a higher number means warmer winters and longer frost-free days, and a lower number means colder winters and shorter frost-free days.

Climate and Weather

Our local climate is influenced by the long-term average of weather patterns. Weather refers to short-term day-to-day or seasonal changes (i.e.: raining one day, snowing the next). When we examine weather patterns over the span of a decade, we call this our climate.

What does “Hardiness Zone 4” mean for the plants in your garden?

When selecting plants from a nursery or looking through seed packages, you can usually find the hardiness zone ranges listed. Anything you see that is zone 4 or lower would survive well in our climate as a perennial. Anything above zone 4 is likely to not survive over the winter and thus becomes an annual.

Photo of two seed packages indicating perennial and zone ranges
Photo of two seed packages indicating perennial and zone ranges

Observing Your Garden

There are some exceptions to planting in our zone (or any zone for that matter).

Take a look at your yard:

  • Where do you get the most sun or the most shade?
  • What direction is your garden facing? North, south, east, or west?
  • Is your garden against a wall or other structure?
  • Do you have raised beds or is your garden in the ground?
  • Is your property more elevated compared to surrounding properties or is it located in a low-lying area?
  • Do you use frost covers or shade cloth in your garden?
Photo of Sarah's backyard garden
Photo of Sarah’s backyard garden showing different microclimates

Some of these factors contribute to what’s called a “microclimate” in your own yard.

Microclimates are small areas (a few meters to a few kilometers) that have different temperatures and rainfall, for example. These unique factors can influence how well your plants grow in different parts of your yard.

A warmer part of your yard may have conditions similar to a garden located in zone 5, for example. This means you may be able to successfully grow “less hardy” plants in that part of your yard.

Factors Influencing Your Microclimate

Let’s examine some factors and what they mean for your garden:

What direction does your garden face?

  • South-facing gardens in the northern hemisphere will receive the most hours of sunlight based on the direction of the Earth’s tilt toward the sun. This means your garden, or parts of it, may be warmer over winter and have conditions similar to zone 5. If you observe the parts of your yard that are the first to melt in the spring, and the last to freeze in the winter, then you likely have a location that is reflective of a warmer zone. This is where you could plant your least hardy ornamental perennials, as well annuals or crops that need full sun. Examples may include cosmos, zinnias, tomatoes, pumpkins, and zucchini.
  • North-facing gardens receive less hours of sunlight and will generally exhibit cooler temperatures. You may have noticed that the north side of your yard will be the last to thaw in the spring and the first to freeze in the winter. Since this part of your yard receives more shade, you can plant the most hardy perennials here like native wildflowers. You can also plant annuals and crops that like shade or part sun such as begonias, coleus, salad greens, peas, and other cool-season crops.
  • East- or west-facing gardens will receive differing amounts of sunlight. Think of these areas as part-sun. If you are east-facing, you will get morning sunlight at a cooler time of day, and if you are west-facing, you will get afternoon sunlight at a warmer time of day. Some sun-loving plants will grow well if they receive enough morning sunlight from the east, and some shade-loving plants will be ok in a west-facing garden if they get enough shade.

Where is your garden located?

  • Observe how the sun travels across your yard and if there are structures, trees, or plants around that are providing shade to your garden.
  • Take a look at any structures in your yard. Your house, garage, or shed provides extra warmth to the soil around it. If you have a south-facing garden planted along the foundation of your house and it receives no shade, this will be the warmest and driest part of your yard. Plant sun-loving, drought-tolerant perennials here. If you are growing crops in this location, ensure they love full sun but be prepared to water them frequently!
  • Is your garden located under or near any trees? How large is the tree? What species of tree is it? Sometimes you may get a little or a lot of shade from a nearby tree. Trees also absorb A LOT of water from the soil. If you are planting native perennials which have deep roots and are more drought-tolerant, this may not be an issue. However if you are planting veggies, you may need to water more frequently. With a large leaf canopy, rainwater is less likely to reach the soil below. Also consider if the tree loses leaves or needles – this may affect the quality of your soil beneath the tree.
  • Is your property elevated compared to the surrounding area? If yes, you may have a warmer, drier, but likely windier microclimate compared to someone who is located in a valley.
  • Low-lying areas usually have cooler, more humid conditions.
Photo of a perennial garden along the side of a garage with two raised beds in the back
Photo of a perennial garden along the side of a garage with two raised beds in the back

What type of garden do you have?

  • If you have an in-ground garden, it typically takes longer for the soil to thaw in the spring. However, your soil would stay frost-free longer in the fall.
  • If you have raised beds or boxes, the soil inside will thaw quicker in the sun as it warms up the outside of the box. However, the soil may freeze quicker in the fall because it is elevated.

Do you use any covers on your plants?

  • If you use structures like tunnels, hoop houses, cold frames, greenhouses, frost covers, and shade cloth, you may be able to push your growing zone. These barriers can also protect your plants from insects and diseases.
  • If you are using an unheated greenhouse or hoop tunnel, you may see a difference of one zone warmer. When adding some heat in the spring and fall to a greenhouse, you may see up to two zones warmer. If you have a sunroom or year-round heated greenhouse, your zones would dramatically increase.
  • If you have indoor plants, you are essentially creating a tropical microclimate. This means your plants experience no frost at all so you can grow desert succulents, tropical plants, citrus trees, and other plants that would never survive outdoors!
  • Shade cloth can also be used to reduce heat and sunlight in your garden. This is useful for cool-season, shade-loving plants like spinach, kale, and broccoli.

Successful Growing in Zone 4

As gardeners in plant hardiness zone 4, we can still grow a wide variety of perennials, annuals, ornamentals, shrubs, trees, and crops.

Perennials, shrubs, and trees that are most adapted to our region will generally grow well here. However, if you have microclimates in your yard that are significantly more wet or dry, experience weather extremes, or receive a lot of road salt, for example, then you’ll need to factor this in to where you plant.

Luckily, some species are more suited than others to these conditions, and some plants are bred specifically to grow well in these areas. Cedars, for example, love consistently moist soil whereas a Spirea shrub may struggle.

Remember that the most frequent causes of plant death are due to the wrong plant in the wrong location.

Final Advice

If all of this this seems too complicated, remember that the two most influential factors to consider are sunlight and water.

Look at your yard, look at where the sun travels, and look at where the rain falls. When you become an observer of both sunlight and rainfall, you can start to identify the different areas of your yard.

  • Annuals are usually forgiving when it comes to planting location, so long as they have at least 4-6 hours of sun and consistent water.
  • Perennials, shrubs, and trees become semi- or permanent parts of your garden however, so this is where a little observation comes in handy.

Reach Out for Help

If you are ever in doubt of what to plant and where, connect with myself, a fellow gardener, or your local horticultural society. The Sudbury Horticultural Society Facebook group members provide a great amount of collective wisdom specific to our growing area.

As well, reach out to the Master Gardeners of Ontario via their Facebook group. Provide them with some information about the location of your garden including photos, and you’ll find that they are always happy to provide helpful advice 🙂

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