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How to protect plants and trees from frost damage


Maple leaf on the ground with frost cover
Maple Leaf in Frost

It's that time of year again where it could be anything from snow to sunshine, rain to drought and everything in-between.


What is a frost date?


A frost date refers to the average or estimated date in a specific location when the risk of frost occurrence decreases significantly. It is a guideline used by gardeners, farmers, and horticulturists to plan their planting and gardening activities.

The frost date typically consists of two important dates:


Last Frost Date: This is the estimated date in spring when the probability of frost occurring is considered low enough that it is safe to plant cold-sensitive crops and flowers without the risk of damage from freezing temperatures. It marks the end of the frost season.


First Frost Date: This is the estimated date in autumn or early winter when the probability of frost increases significantly, signalling the onset of colder temperatures. It indicates that it is time to prepare for protecting or harvesting cold-sensitive plants.


Frost dates are determined based on historical weather data, temperature patterns, and local climate conditions. They serve as a general guideline to help gardeners and farmers plan their planting schedules, ensure proper timing for crop growth and harvest, and take necessary precautions to protect plants from frost damage.


In Ontario, the frost dates are determined by meteorological organizations, such as Environment Canada and local weather stations. Organizations like Old Farmer's Almanac collect weather data and analyze historical patterns to estimate the average dates of the first and last frost in specific regions. The frost dates can vary across different parts of Ontario due to the province's large size and varying climates. Generally, frost dates are determined based on factors like historical weather records, temperature trends, and local climate conditions.


It's important to note that frost dates are estimates and can vary from year to year depending on weather patterns and specific local conditions. Monitoring weather forecasts and consulting with local gardening or agricultural extension services can provide more accurate and up-to-date information about frost dates in your specific area.


Which plants can be damaged by frost in Ontario?


Lemon tree with lemon fruit and green leaves on branches
Lemon Tree

In Ontario, several plants are susceptible to frost damage due to the region's cold climate. Some plants that are particularly vulnerable to frost include:

  • Tender annuals: Plants such as tomatoes, peppers, cucumbers, and melons are sensitive to frost and can be damaged or killed by freezing temperatures.

  • Citrus trees: Citrus trees like oranges, lemons, and limes are not cold-hardy and can suffer severe damage or death in frosty conditions.

  • Tropical plants: Plants like hibiscus, bougainvillea, and banana trees are tropical in nature and cannot tolerate frost. They require protection or should be brought indoors during cold spells.

  • Delicate perennials: Some perennials, such as dahlias, cannas, and certain varieties of roses, may be damaged by frost. While they can recover from cold snaps, protecting them can help preserve their health.

  • Early blooming fruit trees: Fruit trees that blossom early in the spring, such as apricots, peaches, and cherries, are susceptible to frost damage. Late frosts can harm or destroy their flowers, resulting in reduced fruit production.

  • Tender herbs: Herbs like basil, cilantro, and parsley are frost-sensitive and may suffer damage or die if exposed to freezing temperatures.

  • Vulnerable shrubs: Some shrubs, including hydrangeas, azaleas, and certain varieties of roses, are susceptible to frost damage. Their delicate buds or flowers can be harmed by freezing temperatures.

It's important to note that while these plants are more prone to frost damage, the severity of the damage can vary depending on the specific conditions and the plant's health and maturity.


How do I protect my plants from frost damage?


To protect your plants from frost damage, follow these steps:

Allium plant surrounded by fine compost mulch
Allium surrounded by mulch

Monitor the weather: Stay informed about frost warnings and freezing temperatures in your area. This will help you plan ahead and take necessary precautions.


Cover your plants: Use protective coverings like frost blankets, burlap, or old bedsheets to shield your plants from frost. Secure the covers tightly to the ground to trap heat and prevent cold air from reaching the plants. Make sure the cover extends all the way to the ground.


Water your plants: Water the soil around your plants before the frosty night. Moist soil retains heat better than dry soil, helping to keep the plants warmer.


Mulch the soil: Apply a layer of organic mulch around the base of your plants. Mulch helps insulate the soil, preventing rapid temperature fluctuations and protecting the roots.


Move potted plants indoors: If you have potted plants, bring them inside your house, garage, or a protected area like a greenhouse or shed. This provides them with a warmer environment during frosty nights.


Use heat sources: Consider using protective measures like frost cloth or mini greenhouses that incorporate heat sources such as electric heaters, heat lamps, or even Christmas lights. Ensure proper ventilation and follow safety guidelines when using heat sources.


Monitor and remove covers: In the morning, remove the covers once the temperature rises above freezing to allow sunlight and air circulation. Leaving the covers on during the day can cause excessive heat buildup, which may harm the plants.

Remember to tailor these methods to the specific needs of your plants and the severity of the frost.


How do I protect young trees from frost damage?


To protect young trees from frost damage, you can take the following steps:

  1. Select appropriate tree species: Before planting, choose tree species that are suitable for your region's climate and are more tolerant of cold temperatures. Hardy tree species are better equipped to withstand frost.

  2. Water the trees: Adequate soil moisture helps insulate the roots and provides some protection against frost damage. Water the trees thoroughly before the onset of freezing temperatures to ensure the soil retains moisture.

  3. Mulch around the base: Apply a layer of organic mulch around the base of the tree, extending out to the drip line. Mulch helps regulate soil temperature, conserves moisture, and protects the roots from extreme temperature fluctuations.

  4. Use protective covers: For small or newly planted trees, consider using protective coverings such as frost blankets or burlap. Wrap the cover around the tree, ensuring it extends to the ground and is secured tightly. This creates a barrier against cold winds and helps trap heat radiating from the ground.

  5. Install temporary shelters: Create temporary shelters around young trees using stakes and plastic or fabric sheeting. This provides additional protection against frost and cold winds. Ensure the shelter is well-ventilated to prevent excessive heat buildup during the day.

  6. Use heat sources: If feasible, use heat sources like incandescent Christmas lights or light bulbs under the tree cover. This gentle heat can provide extra protection against frost damage. Ensure that the heat sources are installed safely and do not come into direct contact with tree branches or coverings.

  7. Monitor the weather: Stay informed about frost warnings and freezing temperatures in your area. Cover the trees before the onset of frost, and remove the covers during the day when temperatures rise above freezing to allow for air circulation.

Remember that young trees are more vulnerable to frost damage, so providing protection during their early years can significantly increase their chances of survival and healthy growth.


With these tips, your plants should be able to survive to occasional frost that spring has in store! Share your photos and comments with us below, we'd love to hear how you deal with frost in your garden.



Ron Swanson from the show Parks and Rec just realized why it's called May. It May rain, it may snow, it may be 70 degrees or it may be 20 degrees
Gardening in May in Canada


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