Nobody wants their plants to be damaged by an unexpected frost in the spring and fall. If you live in a part of the world where the danger of frost looms over your gardening efforts, this article is for you.
A sudden and unexpected light freeze in the late spring or fall can be devastating for certain plants in your garden.
When the temperature falls below the freezing point during your region’s growing season, it can kill your frost-sensitive plants, including tomatoes, peppers, and cucumbers.
However, you can still help your frost-tender plants come through cold snaps unscathed with these frost protection strategies and tips.
A Word on Freezing Temperatures
When the weather forecast provides a frost advisory in early fall and late spring, that is your heads-up to protect your vulnerable plants and annuals.
Types of Frost Damage
Frost can occur in two forms: hard or light.
What is Hard Frost?
A hard frost occurs when the temperature remains at or below 0 degrees Celsius (32°F) for a few hours.
A hard frost can kill all parts of a plant that are above the ground. It’s much harder to protect plants against a hard frost.
What is Light Frost?
Many folks are surprised to learn that frost can occur between 0 and 2 degrees Celsius (32-35.6 degrees Fahrenheit). This is known as a light frost or light freeze. A light frost causes damage to the tips of tender plants, while the larger parts often remain green.
A late spring or early fall cold snap usually involves a light frost.
Know Your First and Last Frost Dates
The growing season for your climate has a first frost date and a last frost date. While these dates cannot guarantee safety against the threat of frost, you can use them as a guide to help you thwart that unexpected fall or spring frost.
As a gardener, your frost dates should be based on 2 degrees Celsius (35.6°F) to avoid the risk of any plant death.
Which Plants Require Frost Protection?
The following types of plants are most susceptible to frost damage
- Most flowering plants
- Most plants that bear fruit in warm temperatures
- Colorful annual flowers
- Trees and shrubs that blossom in early spring
- Most potted plants
- Tender perennials
For these frost-sensitive plants, you’ll want to keep an eagle eye on the weather forecast until the danger of frost has passed, and be ready to jump into action at any impending cold snap.
Obviously, tropical potted plants such as string of turtles and calamansi cannot handle the winter season outdoors if you live where temperatures dip near freezing. Keep plants like these indoors from the first warning of cold temperatures until the last frost of spring is well behind you.
Choose Cold-Hardy Plants for Frost-Prone Climates
One aspect of protecting plants from freezing temperatures is choosing plants that are less frost-sensitive.
Even cold-hardy plants, however, are still susceptible to being damaged by frost if the cold temperatures drop below 32°F (0 Celsius) and stay there for a prolonged period of time.
Plus, sometimes you just want to grow frost-tender plants, anyways. Here’s how to provide your plants with adequate protection.
Ways to Protect Your Plants from Freezing Temperatures
Here are some tried-and-true frost-protection strategies for those light frosts that come at the most inopportune times.
1. Move Container Plants Indoors
When plants are young, they require shelter from the frost to prevent damage. Protect tender plants by moving them indoors whenever possible. Plants that are in their nursery, as well as small-container gardens, are usually easy to move around.
For example, if you’re growing pepper plants in pots, you can easily move those indoors. Ditto to potted tomatoes, cucumbers, and other garden plants
To protect against a light frost, even an unheated and un-insulated indoor location is sufficient. A garden shed or garage will suffice.
However, if the temperature drops well below 32°F (0 Celsius), you’ll need an insulated and/or heated indoor space to provide adequate frost protection. Move plants indoors to your home, a heated garage, or some other indoor space that can maintain temperatures above 2 Celsius (35.6°F).
2. Keep Plants Warm By Choosing Frost-Resistant Locations
The cold air and wind will pass through plants located on slopes or higher ground as it sets in on lower ground. Therefore, it is best to place susceptible plants on higher ground.
In addition, if plants are facing west or south, try to ensure that there is a wall, fence, or bench nearby. This will be helpful if you use dark-colored structures as they will be able to absorb heat during the day, keeping plants warmer throughout the night.
3. Water Plants During the Day
Before the prediction of evening frost, water your plants thoroughly during the day. This is because damp (but not entirely wet) soil can hold four times more heat than dry soil. Plus, it will also conduct heat once the soil releases moisture.
So, when the temperatures dip overnight, the soil will be able to retain more thermal heat that will help protect the plants.
4. Use a Cold-Frame or Clothes
Seed-raised perennials, hardy shrub cuttings, and autumn-sown hardy annuals are young, hardy plants that will benefit from the shelter of a cold frame during winter. You can open the lid when the days are warmer to deter fungal diseases and prevent overheating.
Alternately, you can also cover the plants with clothes during frost to retain heat and moisture. Providing adequate shelter and protection to winter crops during harsh frost can make all the difference to their chances of survival.
5. Add Mulch
Adding an extra layer of mulch, including compost or shredded bark, can provide insulation for tender plants. Be sure to cover the plants before frost begins (a night before) and remove it when the weather starts to warm up again.
For large planting areas, however, labor-intensive and messy mulching may not be the best solutions. Generally, this method should be reserved for plants that are in an area where extra mulch can easily be spread out when the weather warms up or for plants that are sturdy but small.
6. Harden Off Seedlings
Acclimate the seedlings to the outdoors before setting them out. This will gradually get them used to the outside conditions. This process is known as hardening off and will help plants grow stronger.
The process should ideally begin 14 days before transplanting during mild weather. You can place the seedlings in a shady spot outside when the weather is warm. Be sure to bring them in at night, though. The seedlings will eventually grow sturdier and stronger after two weeks.
7. Cover the Plants
If temperatures aren’t going to get too cold—a degree or two below freezing—then covering plants can often prevent frost damage.
Cover your plants before dusk to prepare them. Most of the heat in the garden will dissipate if you wait until darkness falls. Make sure that the cover falls down to the soil on either side, no matter what type of covering material you use.
Do not cover up the plants all the way to the trunk. This will prevent the heat from the soil from reaching the plant. Make sure that there are no openings left for the warmth to escape.
If you want to prevent the cover from touching the foliage, you can use stakes. The covers can be removed after the frost has thawed in the morning and the weather is warmer.
Remove the cove r when the frost danger has passed, such as during the day. If you do not remove the cover, the plant will start growing again, which can cause more damage during the next frost.
8. Place Containers over Tender Plants
In the spring, you can place large containers over tender young seedlings that are most vulnerable to frost. If it is too windy, use bricks or rocks to weigh the containers down. Buckets, storage totes, and other large containers work well.
The container will create a pocket of insulation around a plant, preventing cold air from seeping in. In addition, it will also trap heat from the soil near the plants, helping them stay warm. When the temperature warms up in the morning, remove the covers.
9. Warm Plants Using Water Jugs
Use jugs of warm water to prevent plants from freezing. Use water jugs, plastic milk jugs, or juice jugs. Fill them with water. Allow them to soak up the heat during the day by placing them under the sun in warm weather. Set these jugs around the plants during the night and cover them up with a sheet.
The warmth that each jug emits emit will protect plants from a light frost.
10. Wrap the Trees
Wrap the trunks of the fruit trees in the fall to prevent damage from frost. You can use a tree wrap or burlap strips for coverage. When temperatures fluctuate, trees with thinner barks are more susceptible to damage and splitting.
Hence, using a tree wrap can prevent splitting (also known as frost crack).
It is better to keep the wrapping loose and cover the trunk with weatherproof paper or cloth layers to provide better insulation. Extend the cloth as high up s the lower branches or limbs and extend it all the way to the ground. You can leave the wrapping on throughout the winter.
11. Allow the Air to Pass
Professional farmers often move air at large volumes to keep a light frost at bay.
This method involves the use of a large fan with a chimney that allows warm air to reach the ground while it pulls up cold air. Some farmers also use low-flying helicopters that hover over the plants to keep the air moving.
Although these are great solutions, they are not viable for a home gardener. As a home gardener, you may use an electric fan to create an artificial breeze.
Alternately, you can also use a powerful blower to stimulate the air. You can place the fan or the blower near the pot.
Frost Susceptibility Factors
1. Age of the Plant
The age of the plant matters a lot when it comes to dying from frost. Younger and tender seedlings are usually the most vulnerable to frost attacks.
The proximity of other plants and structures can make a difference in the plant’s chances of survival. Without having any close plants or structures, such as a fence, to provide shelter, plants can die as they are exposed to cold winds.
Having a shelter ensures that heat is radiated back to the plants during the winter season.
3. Type of Soil
The heat typically radiates off the soil at night when it is warmed up by the sun during the day. The soil will release more moisture in the air if it is fertile, heavy, loose, and deep.
Higher humidity reduces the chances of frost being formed on the plants as it slows down the rate of temperature change and raises the dew point. This also explains how the temperature in desert areas is changed from extremely hot to freezing cold.
The plants will eventually become more susceptible to the cold of the night if they don’t have enough wind to mix the falling cold air with the rising warm air.
6. Cloud Coverage
Your plants will stand a better chance of defending themselves against frosts if there are more clouds in the sky to reflect and absorb heat back down to the earth.
We hope that this article helped you understand how to protect plants from frost. If you notice any frost damage, don’t panic and don’t take any drastic steps. Many plants are surprisingly resilient to frost and might even bounce back afterward.
The best thing you can do is wait until the weather starts to warm up again and check if any new plants sprout.
Looking for more ways to protect your plants? Read this article on making All-Natural Pesticides to keep your plants safe from pests.