Dealing with frost can be an exercise in frustration, damaging your tender seedlings, annuals, and heat-loving vegetables.
Learn how to protect your plants from frost damage with these easy and affordable tips.
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There are few things as disappointing as losing plants to a cold snap.
Whether it’s a beautiful annual that you bought from the garden centre, or (worse, in my opinion) a tender new plant that you’ve grown from seed, losing a plant to frost damage sucks!
So what can we do to protect our plant babies from getting frostbite?
First, we need to understand what we're dealing with.
❄️ The Difference Between Frost and a Freeze
Frost can develop when temperatures reach 0°C (32°F).
There are technically different kinds of frost, but for the sake of keeping things simple let's say that frost is a thin layer of ice that forms when the water vapour in the air becomes solid on the ground or on solid surfaces.
When frost forms on plants it can cause various kinds of damage. The extent of the damage will depend on the cold hardiness of the plant and the length of the exposure, among other things.
On the other hand, a freeze is pretty much what it sounds like. The temperature is so cold that water will turn into ice, including the water inside of your plants.
If you live in a cold climate, you know that your garden will freeze over winter. However, there are times in spring or fall where you might get a flash freeze, which requires you to protect your plants.
Did You Know? We don't usually have to worry about snow harming our plants. Snow actually acts as an insulator and keeps the soil warm, which can protect plants from cold temperatures.
Why Does This Matter?
Protecting your plants from frost requires a different approach than protecting your plants from a freeze.
Not all plants are negatively affected by frost. In fact, some vegetables (like carrots, kale and Brussels sprouts) actually taste better after they've been exposed to frost.
A freeze, on the other hand, can be damaging to even cold-tolerant plants.
🌱 Which Plants Should You Protect from Frost?
If a plant thrives in warm weather, it probably needs to be protected from frost.
Think about the types of annual flowers, herbs and vegetables that you plant in the warm months. These are all likely to be cold-sensitive plants that need protection.
This includes (but isn't limited to):
- tomatoes
- eggplants
- peppers
- beans
- okra
- melons
- citrus
- basil
- begonias
- impatiens
- hibiscus
- bougainvillea
Additionally, any tender young plants and seedlings will benefit from frost protection.
Now that we know what frost is, and which plants can be damaged by it, let's talk about an action plan for dealing with it.
🗓️ Learn Your Frost Dates
The first course of action when it comes to protecting your garden from frost is understanding when there’s likely to be frost in your area.
Frost dates are based on historical data and gives us an estimate of when we may have frost in the spring and fall seasons.
A mistake that new gardeners sometimes make is planting out warm-weather plants before the threat of frost has passed.
By learning your frost date, you can get a better idea of when the weather will be warm enough to safely plant out cold-sensitive plants. This can also help you plan when to start your seeds so your seedlings can be planted out at the appropriate time.
🌨️ Check the Weather Forecast
In addition to knowing your frost dates, you also need to keep an eye on your local weather forecast.
Here in Southern Ontario (Canada), our spring weather can fluctuate from 30°C (86°F) to -2°C (28.4°F) in a matter of days.
Monitoring both your short and longterm forecast will help you figure out how to best protect your plants from extreme weather.
Tip: The Weather Network app and website are excellent resources for monitoring the weather forecasts across Canada.
🪨 Gather Materials for Covering Plants
When I worked at my garden centre job, we had something called a frost kit. This was essentially a giant storage bin filled with the supplies that we needed to cover up the tender plants that were exposed to the elements.
You can create your own frost kit by collecting the following supplies and keeping them in an accessible place for last-minute frost protection.
Frost Cloth (Garden Fleece)
Frost cloth, sometimes called floating row cover or garden fleece, is a breathable non-woven fabric made out of polypropylene that has multiple uses in the garden.
Lightweight garden fleece (weighing about .5oz per square yard) allows about 90% of light to shine through and is great for protecting seedlings from insects. Since it has a high amount of light transmission, it can be left covering the plants for long periods of time. However, it may provide little to no protection against frost.
In order to properly protect your plants from frost, look for a medium or heavy weight row cover that specifies how much protection it can provide.
For example, a medium weight garden fleece (weighing .9oz per square yard) might say that it provides "up to 4°C frost protection" or "protects down to -3°C (26°F).
A heavy duty garden fleece (weighing 1oz per square yard) might state that it "offers protection down to -5°C (23°F)". Heavy weight row cover can also be used to wrap shrubs, trees, or perennials to protect them from a freeze.
How to Use Frost Cloth
- Loosely drape the material over your plants and secure the ends by weighing them down with bricks or rocks.
- If your plants are tall, support the weight of the fabric with plant stakes or hoops to make a tent-light structure over your plants.
Note: If you have purchased "frost protection fleece" from a popular Canadian dollar store (like I have in the past), you may want to try doubling the fabric to make a thicker layer over your plants. Even though the product says "frost protection" it's actually a lightweight fleece (weighing approximately .4oz per square yard) which is better suited to insect control than actual frost protection.
Garden Cloches
A cloche is a just a cover that you place over your plants to protect them.
The original garden cloches were bell-shaped and made from glass, but modern cloches are usually made of plastic.
You can make a DIY cloche out of any large plastic container, like a 1 gallon milk jug, or just use a plastic plant pot or a cardboard box.
To cover a plant that it’s the ground or a raised bed, place the cloche over the plant and push it about an inch deep into the soil.
If you’re covering a large heavy pot that can’t be moved, you can rest your cloche on the rim of the pot and weigh it down with a rock on top.
You'll be covering up your plants to protect them overnight, and you'll need to remove the cloches by mid-day or your plants may overheat or collect too much condensation (which will subsequently freeze on your plants the following night).
🪴 How to Protect Plants in Containers
Plants that are in pots are more susceptible to damage in cold temperatures, as they don’t have the benefit of in-ground heat. Luckily, they’re also the easiest plants to protect.
Here's an easy method that I use:
- Group pots and containers together and place them under shelter. This could be right next to the house, where it tends to be a bit warmer. For more protection, you can tuck them inside of a garage or shed overnight where they won't be exposed to the elements.
- Moisten the soil. That might seem counterproductive, but water actually increases soils capacity to hold heat. You're aiming for damp soil not soaking wet soil.
- Cover the group of pots with frost cloth, or cover them individually with a cloche. This will help to trap the ambient heat that comes up from the soil.
You're going to cover up the plants in the evening so they're protected overnight and into the early morning.
Once the threat of frost has passed the next day, uncover your plants or bring them back outside so they can get light.
If you're expecting a flash freeze, you can move the containers into a cool place in your home instead. Just inspect the plant for insects and pests first, to avoid bringing anything unwanted into your home.
🌿 How to Protect Plants in Raised Beds and Planters
Any plants that are in raised beds or planted directly in the ground can also be protected with damp soil and some kind of cover.
The method is similar to above, with a few minor differences:
- Moisten the soil around the plants. Again, you're aiming to make the soil damp not soaking wet.
- Optional: add mulch around the base of your plants for additional warmth.
- Cover your plants with frost cloth or with cloches. You can cover an entire raised box or bed with a single piece of frost cloth if it's large enough.
🙋🏽 Frequently Asked Questions
If you don’t have frost cloth, you can use an old bedsheet, blanket or towel.
Just keep in mind that these options are heavier than frost cloth and therefore should not be placed directly on top of plants. Instead, drape them over stakes or hoops to create a tent above your plants.
You will also need to remove these items during the day to allow your plants to get light.
Yes! You can definitely cover your plants with a cardboard box. Make sure it is large enough to cover the entire plant. If you are going to have consecutive nights of frost, you may want to make sure that your box isn't getting soggy or it could collapse onto your plants after a while.
When temperatures dip anywhere near 0°C (32°F) you should take precautions to protect your cold-sensitive plants.
Cloth provides excellent protection for plants, but if there's a risk of your plants freezing you can drape a layer of plastic over your frost cloth for extra protection.
Lightweight frost cloth can be laid directly over plants with no issues. Plastic can get very cold and actually freeze to your plant leaves, causing more damage. If you're going to use plastic, be sure to drape it over stakes or a frame so it's above your plants.
This article about how to protect plants from frost was originally published in 2021. It has since been completely re-written and re-published with new information and photographs.
Michelle says
Oh it’s so tempting to get out in the garden but I will wait for Victoria Day weekend. In the meantime, I’ll enjoy looking at the seedlings I started indoors that are starting to outgrow their pots.
Shareba says
That's fair! We should be past the threat of frost around then too - I can't wait! Hope your seedlings do well!