If you’re a “fresh-out-the-oven” plant enthusiast, you might wonder what temperature is frost for plants exactly? An accurate answer to this question is difficult to give, mainly because plants, like humans, can perceive various degrees of cold.
It’s one thing to have to endure 32 °F (0 °C) for a couple of hours and an entirely different thing to spend a couple of minutes at 5 °F (-15 °C), especially for a plant.
Plants and Frost Temperature
Frost is the first thing you should worry about when you add plants to your outdoors – gardens, balconies, or terraces. When wondering what temperature is frost for plants, you should also consider the frost and freezing date and duration in your location.
Some plants can withstand harsh temperatures every night as long as daytime provides warmth to keep them alive. Others, however, will die if exposed to certain temperatures, even for a short period.
What Temperature is Frost for Plants?
Most plants develop and blossom mainly in the spring. Unfortunately, this is also the time when temperatures are at their harshest, especially in temperate-continental climates.
Low temperatures become dangerous for plants when they cause the ground temperature to drop below 32 °F (0 °C).
When this happens, frost begins to form on the plants. Slowly but steadily, frost impacts the way water moves through the plant.
At the same time, the more frost is present on a leaf, the less water a plant receives, as the leaves’ cells practically freeze.
What Plants are More Susceptible to Frost Damage?
As a general rule, frost can damage or kill plant cells. Consecutive freezing and thawing of the plant strengthen this effect. In short, even the most resilient plants will have difficulty resisting exposure to below-freezing temperatures every night.
On top of that, stronger winter winds bolster the effect of frost. These become cold; low-temperature winds remove moisture from leaves faster than the plant can supply.
Young plants, especially those freshly planted, are more susceptible to frost damage as they’re not fully developed. The air close to the ground’s surface is also colder, making it extremely difficult for growing plants to resist frost.
On the other hand, hardy plants survive the cold seasons better, but they still need to be sheltered away from the wind. Few plants can withstand both frost and cold winds in an open field.
Young tender plants don’t resist frost well at all. On the other hand, adult plants that have had the chance to mature are more resilient and can resist winters a bit better. Remember that they still need more protection than hardy plants.
What are the Different Types of Frost?
There is a single type of frost, namely the one that appears when temperatures drop below 32 °F (0 °C).
When it comes to frost, the single most important thing (for plants) is the duration of this phenomenon. The longer plants suffer from frost exposure, the fewer their chances of survival.
Instead, there are different types of “freeze” – in theory, different frost temperatures. The three types are:
- Light freeze – occurs between 29 °F and 32 °F (-2 °C and 0 °C). This type of freeze will kill young tender vegetation but has little effect on other types of plants.
- Moderate freeze – occurs between 25 °F and 28 °F (-4 °C and -2 °C). This type of freeze has wide destructive effects on most types of plants and will likely kill vegetation classified as tender, semi-hardy, and fruit blossoms.
- Severe freeze – occurs when temperatures drop under 25 °F (-4 °C). This type of freeze damages most types of plants.
As you can see, when it comes to “what is freezing temp,” things are different for plants as they are for humans.
Excessive temperature variations, however, are too much for plants, as even changes of a couple of degrees can make the difference between a rich harvest and a dead plant.
What are the Frost Dates?
The term “frost dates” refers to the first and last days of the year when you should expect frost to occur. As such, the first frost date usually occurs during fall, when temperatures start to drop.
Freezing temperatures follow frost, and there’s a first freeze date as well! It usually occurs when temperatures drop below 32 °F (0 °C).
On the other hand, the last frost date usually occurs during spring, when temperatures start to rise back up. Most states do keep a record of the first and last frost dates (the averages result from 30 years of historical weather data for most states and countries out there).
Don’t forget that these dates might change from year to year. It’s a good idea to keep an eye out for the daily weather report in the fall and spring for safe measures.
What are the Least and Most Resistant Garden Plants?
If you’re looking for a quick and to-the-point answer regarding the resistance of your garden plants, here’s some essential information on that. We don’t get into flowers and such since people usually keep them indoors – or at least you can easily move them indoors if frost takes you by surprise.
Some of the least resistant garden plants are spinach, asparagus, cucumbers, tomatoes, sweet corn, and beans. Frost will damage these plants at temperatures between 30 °F and 34 °F (around -1 °C).
Some of the most resistant garden plants are okra, broccoli, cabbage, carrots, and peas. Frost will damage these plants at temperatures between 26 °F and 30 °F (-3 °C and -1 °C).
How to Protect Plants Against Frost
Now that you know everything about frost and freeze regarding plants, it’s time to show you some tips, tricks, and strategies you can use to protect plants from frost.
Remember that most of these work before the first frost actually kicks in. There is little that you can do to reverse frost damage – mostly, you just have to hope that it wasn’t too serious and that your plants will eventually snap out of it!
Avoid Planting Vegetation in “Frost Pockets”
OK, we might not have told you everything there is to know about frost – let us make up for that right now!
We mentioned that the air closer to the ground’s surface is cooler. This occurs primarily on near-sloped surfaces. When meeting slopes, cold air flows downward and stops when it meets a barrier or when it reaches the lowest point of your garden in this scenario.
Cold air becomes trapped in those points, becoming a frost pocket that can cause permanent and continuous damage to your plants.
This is the main reason why planting location is just as important as planting time, for example.
Plant Vegetation That Fits Your Growing Conditions
Avoiding frost pockets is not enough if the plants you chose are not hardy enough to survive in your region. But how do you choose vegetation that fits your growing conditions?
Well, when it comes to garden plants such as vegetables, we’re talking about planting and harvesting times. The latter occurs, in most cases, right before the first frost date.
As such, you must determine the first frost date of your region and then the latest harvesting date for the vegetables you want to plant.
If the two don’t intersect, then you’ve found the plants that will fit in your garden and, at the same time, that you’ll harvest right before the first frost and freeze dates.
Rely on Horticultural Fleece if Needed
Horticultural fleece is essentially nonwoven fabric consisting of polypropylene. People use it to cover plants for frost or as “floating mulch.” Unlike actual wool, it is pretty thin.
It has the purpose of protecting delicate plants, as well as early and late crops. Naturally, it does wonders when you use it on plants susceptible to frost and cold weather.
You should just “throw it over” the plant or plants in question, and it will keep them warm. If you don’t have access to horticultural fleece, you can rely on other types of plant covers for cold weather – comforters, bed sheets, towels, pillowcases, and cardboard boxes.
Mulching is the Friend of Tender and Evergreen Plants
Covering plants for frost is sometimes not enough, especially if the first frost date has occurred already. In this scenario, you can rely on mulching!
You can mulch tender perennials (and shrubs) and evergreen plants with organic matter around the root area before the cool season. Mulch helps the soil maintain a steady temperature and prevents frost, as it has an insulating effect.
In contrast, you can also use organic matter mulch during summer to keep the ground cooler and prevent overheating in vegetation. Naturally, mulch works best in regions with excessive temperature fluctuations.
Prioritize Plants and Come Up With a Course of Action
A general rule for protecting plants from frost refers to identifying your hardy and tender plants and ultimately focusing more on the tender ones. Depending on your region, most hardy plants won’t have any issues getting through the first weeks of winter. They will resist through some frosty days as well.
Conversely, tender plants will let go of their harvest, so to speak, as soon as frost or freezing temperatures come around.
Once you prioritize your plants (separate the hardy from tender ones), the second wave of prioritization follows. More specifically, you have to separate between plants that you know have a rich harvest and those that haven’t been fruitful lately.
Obviously, you’ll want to focus your protective measures on the tender plants that are likely to have a lot of fruit, and that will ripen during the first frost period.
Water is Still a Plant’s Best Friend, Even During Frost
Water insulates the soil around plants. As such, wet soil conserves heat and will increase temperatures at the root level of your plants. At the same time, water-rich plant cells are stronger against frost, freeze, and subsequent damage.
When you know the first frost or freeze date is nigh, you can soak the soil of your plants as a damage preventive measure, at least in the case of hardy plants. Still, you have to move or protect tender plants.
Plant Late and Harvest Early
Horticultors plant garden vegetation mostly during spring. Spring is also the season when significant frost can occur. As a result, you should plant sensitive crops a bit later. Remember that doing so won’t affect the growing process of your plants. Warm weather is enough for them to catch up.
Late planting is also helpful to your plants in the long term. If you do not expose your vegetation to cold temperatures, it will become more resistant to diseases and pests.
When it comes to harvesting, remember that most fruits and vegetables (such as plums, tomatoes, and apples) continue the ripening process even after you’ve picked them.
Therefore, you can play the “cautious” card and harvest them right before the first announced frost date (to avoid damage).
Keep a Close Eye on the Daily Weather Report
When fall settles in, it’s a good idea to keep a close eye on the daily weather report. As soon as the officials predict the first night with freezing temperatures, you should start taking the appropriate measures (mentioned above) to protect plants from frost and freezing.
If you’re new to vegetation planting and growing, this is probably the best thing you can do. It gives you a much-needed heads-up that your plants might soon be in danger!
The Bottom Line
In the end, it is safe to say that horticulture can be quite difficult, especially when your garden starts taking shape and there’s a plant in every corner that you need to take care of.
Naturally, like with many other hobbies or professions, things are difficult until you get the hang of them.
As such, consider this article an introduction to frost and low temperatures regarding vegetation, as well as to how to protect plants from frost.
You will gain access to the remaining information as you experience frost and freeze dates, as well as some vegetation damage – it’s bound to happen, after all!
Remember the best piece of advice, however – namely, keep an eye on the weather report. As soon as temperatures revolve around the 32 °F (0 °C) mark, you must start focusing on and protecting the plants in your garden!