Early or late frosts can be disastrous if you’re not prepared. A single moderate frost can decimate your less hardy fruit and vegetable plants. Knowing how to protect your plants from frost, both unexpected frosts and regular frosts, can keep your plants productive for longer, which is always a good thing. We try to plan our growing areas with frost protection in mind to extend our growing season for as long as possible. But there are always those unexpected frosts that can still kill off tender fruits and veggies too early, so we’re always ready to take some last-minute action to protect our plants.
When to Expect Frost
When to expect frosts really varies based on your location, of course. You can use the USDA’s plant hardiness zone map to find your zone, (just place your cursor over the map below to zoom in). Then look at our table of first and last frost dates to get the general guidance for when to expect frosts in your area.
First and Last Frost Dates
|USDA Hardiness Zone||Approximate First Frost||Approximate Last Frost|
|1||Aug 25 – Aug 31||May 22 – June 4|
|2||Sept 1 – Sept 8||May 15 – May 22|
|3||Sept 8 – Sept 15||May 1 – May 16|
|4||Sept 21 – Oct 7||April 24 – May 12|
|5||Oct 13 – Oct 21||April 7 – April 30|
|6||Oct 17 – Oct 31||April 1 – April 21|
|7||Oct 29 – Nov 15||March 22 – April 3|
|8||Nov 7 – Nov 28||March 13 – March 28|
|9||Nov 25 – Dec 13||Feb 6 – Feb 28|
|10-13||No frost||No frost|
Remember, though, that this is only general. There’s no way to give you specific dates. But what you can do is get better at predicting when a frost is likely, which we’ll discuss in more detail below. I would also assume a frost is likely two weeks either side of these first and last frost dates so you’re less likely to be caught off guard.
Remember, too, that these dates cannot compensate for the microclimate in your growing area. If it’s very exposed or in a deep valley, for example, it’s more likely to experience frosts earlier and later than the dates specified in this table. Similarly, if you’ve got lots of protection in the form of trees, walls, and natural heatsinks, your growing space won’t be as troubled by freezing temperatures as early or late.
How to Protect Your Plants From Frost
We use a combination of methods to protect our plants from frost. We plan in advance as much as we can, and we’re ready to leap into action if it looks like there’s going to be an unseasonal frost. We still get caught out from time to time, of course, but less so now we plan our gardens for frost protection, we know our soil and our local climate, and we are getting a little better each year at predicting if a frost is likely.
1. Use Frost Blankets for Plants in Rows or Beds
Frost blankets or garden fleeces (these ones are good value) are a nice, simple answer to frost protection for most crops. The fleece is light enough to allow light and moisture to penetrate, but insulating enough to ward off light to moderate frosts. Frost blankets are one of my main go-to’s for protecting long rows and beds quickly and easily.
Remember to weigh them down well so they stay in position during harsh weather and strong winds. I’ve been caught out a few times by not weighing the fleece row covers down properly, only to find they’ve blown off during the night and I’ve lost the delicate plants beneath to the frost.
In a pinch, you can also use actual old sheets and blankets to cover crops overnight. Don’t do this until evening, though, as you don’t want to unnecessarily block out the light. And for the same reason, you’ll need to remove the covers in the morning as soon as the temperature rises above freezing.
We try not to do this, and always keep a supply of garden fleece or frost blankets on-hand, but when you’ve got more ground to cover than yards of fleece available, you’ve got to protect your crops somehow, so we have been known to throw old blankets over hoops to cover late strawberries, tomatoes, and similar.
2. Use Individual Plant Covers or Winter Cloches
Some plants need extra protection, you have a few frost-tender seedlings growing early in the season, or you’ve still got a handful of plants trying valiantly to ripen as winter draws near. You don’t need a whole fleece blanket in these situations – and cutting them down just to cover a few plants is wasteful (and will bite you in the ass later in the year when you need to cover a large area).
In these situations, we use individual cloches. But we don’t tend to go buy the fancy ones. Instead, we use plastic bottles. 2-liter soda bottles are great for small or young plants, like early peas and beans. And for larger plants, we like the big 1-gallon jugs.
Now, if you only plan to leave the cloches on overnight, you can just cut the bottom off the 1 gallon jug or cut a 2-liter bottle in half and place them over your plants. But if you want to use these as frost protection and mini-greenhouses any longer than that to help you get an early crop or just because the weather is going to stay colder for longer, then you need to cut another hole at the top (or take the lid off the bottle) to let the plant breathe and to let moisture escape. If you don’t, the plant you’re trying to save will die.
3. Add an Extra Thick Layer of Mulch
Mulch provides vital insulation. It protects root systems by trapping moisture and warmth and retains and radiates warmth to the plants above ground, too. The key to using mulch to protect your plants from frost is to add a layer of around 3 to 6 inches across the top of the soil. But, you should also leave around a 1 inch gap around the plant stem to allow the warmth captured in the soil to radiate up to the plant.
Leaf mold works really well, as does wood chips (assuming that you don’t have chips from pines or other wood that inhibits the growth of other plants). You can also use straw.
4. Wrap Young Trees and Blossoming Trees
Tree wrapping is pretty self-explanatory. If a frost is likely, get outside and wrap up your young trees. I’d recommend doing this at the first sign of winter anyway if you have very young trees, particularly fruit trees. Many young trees (up to about four years old) are particularly at risk of significant frost damage which can stunt or slow growth, reduce crop yield, or, in the worst-case scenario, can kill them outright.
In spring, even if a fruit tree is older and generally able to withstand winter frosts, if it already has blossoms or very full buds, an early frost can wipe out this early growth and decimate any crop yield for that year, so providing insulation at any hint of a late frost is a sensible precaution.
You can use burlap, rags, cardboard, fleece frost blankets, old blankets – anything that’ll provide some degree of insulation. You can also use these felted tree protector wraps which are a good option in colder climates. Another clever natural idea is to use rush or straw screens to wrap around the trees to act as insulation.
To successfully protect a tree from frost with wrapping, take your wrapping material and, starting at the base, place it around the trunk, overlapping each layer and working your way up. Periodically secure the wrap with twine as you work your way up. Stop when you reach the lowest branches. If the tree is very young, you may also want to consider adding some of the same frost protection to the branches you can reach, too.
You can also add a layer of plastic sheeting, like a tarp, over the wrapping at night or for a few days if an extra hard cold snap is forecast. This adds an additional layer of insulation and traps warm air between the plastic and the wrap beneath.
If you’re trying to protect delicate blossoms and buds, you can use bubble wrap to gently wrap those branches and insulate them against frosts.
5. Plant Your Garden to Minimize Frost Damage
If you take frost into consideration when you’re planning your garden for the year, you can minimize the likelihood and extent of frost damage. It just takes a little bit of forethought.
If your garden is uneven, make sure you place tender plants (those most likely to sustain frost damage) at the highest elevations. Hot air rises and cold air sinks to the lowest points, so plants in the highest locations available in your growing space will stay warmer. When there is a significant difference in elevation, such as in a deep valley, the temperature can be as much as 18 degrees colder in the depths of the valley than the surrounding high points.
Plants that are exposed are at greater risk of frost damage, so don’t plant delicate things out in the open with no protection. Use taller or more robust plants as well as rock formations and walls as windbreaks.
If necessary, create some windbreaks from plastic sheeting and bamboo canes to keep tender plants from exposure-based frost damage. Consider where you already have natural windbreaks, such as fences, trees, and hardy shrubs and make use of those features when planning where to plant your tender edibles.
Additionally, rock formations and brick walls absorb heat during the day and it slowly dissipates overnight, meaning they act as natural heatsinks. So make use of this – plant tender plants and those only able to withstand the mildest frosts close to walls and large rocks.
For the tenderest plants, think about planting them in raised beds. These warm more quickly and are usually easier to cover than regular crop rows.
6. Bring Delicate Potted Plants Indoors
If you’ve got things like herbs and other plants that don’t tend to overwinter very well, and you’ve sensibly put them in pots already, bring them inside. Even if it’s just overnight when you suspect a frost is on the cards. Just make sure that you leave them in a garage or unheated conservatory – you don’t want to overheat them, particularly if you want to get them back outside in a few days or early in the year. They’ll never survive the intense temperature change. So make sure the room you choose to store them in gets plenty of light but not too much heat.
Remember, plants in pots are much more likely to sustain damage from frost than those planted directly in the ground, because they don’t benefit from the insulating properties of the earth and mulch.
7. Learn How to Predict a Frost
There’s no way to predict a frost that’s 100% foolproof, but you can use your knowledge of your local climate and good old fashioned commonsense to predict a frost with a pretty good success rate. If it’s cloudy and windy, it most likely won’t freeze, because the clouds act as a layer of atmospheric insulation, preventing the heat of the day from escaping so rapidly during the night. And the wind keeps the air moving, stopping pockets of cold air from settling.
However, if the sky is clear and the air is still, this has a cooling effect, allowing the warmth of the day to escape into the atmosphere. This will most likely lead to a frost.
Keep an eye on the thermometer during the day, too. Did the temperature in your garden reach 75F (or 80F in the Southwest)? If so, there’s very little chance of you seeing a frost during the night.
8. Make a Simple Heatsink For Your Cold Frame or Covered Rows
This one is a simple tip that works surprisingly well. Fill up large 5-gallon jugs with clean water, tighten the lids, and place them all around the edges of your greenhouse or around the perimeter (but on the inside) of your frost blanket, surrounding your plants. The water absorbs heat during the day and slowly releases it overnight, helping to prevent frost damage. It’s simple but very effective.
You can also fill up the milk bottles or jugs with hot (but not boiling) water and place around your plants in the early evening as temperatures start to drop. That’ll keep your plants warmer for longer.
9. Add Plenty of Good Compost to Your Beds
This one is a preparation tip: Make sure you dig in plenty of rich compost before you plant. If your soil contains lots of rich organic matter, it has better structure, retains moisture without getting boggy, and overall performs better. And, because of all that organic matter and healthier structure, your soil will stay warmer and protect delicate root systems.
The breaking down of the organic matter also releases heat in the soil, further raising the temperature.
10. Water in the Middle of the Day
If there’s any sign of a frost and the ground is dry, get out there and water – in the middle of the day. Wet soil holds heat better than dry and watering in the middle of the day ensures the water has time to soak right in before the temperature drops and freezes the water, which can kill the roots of your plants.
Just make sure you don’t saturate the soil as you increase the risk of the water not soaking in effectively and then freezing overnight which can kill the roots and therefore the plants.
What to Do After a Frost
If you are caught unawares by an unseasonable frost or all your preparations still resulted in some plants getting frostbitten, try not to be too disheartened. First, check for signs of damage – these usually include wilted, brown, or black leaves and foliage. Or the whole plant may have shriveled and fallen over.
Firstly, don’t warm them up too fast. Let them warm naturally or give them a little gentle encouragement with some bottles of hot water placed around them to raise the temperature. But don’t handle them yet – plants are exceptionally fragile while they’re frozen, so wait until they’ve thawed before you touch them.
Don’t be overly eager to prune or pull up the plants. Wait at least until the afternoon before you decide which ones need to be culled. If at this point only a few of the uppermost leaves are wilted, simply prune them off and your plant will recover.
However, plants that have a lot of blackened leaves and stems most likely will not recover – or, if they do recover, they won’t be healthy or productive. These are the plants I’d pull up and (if possible) replace.
Which Vegetables are Vulnerable to Frost?
Any of your heat-loving crops and summer season crops cannot tolerate even mild frosts. Other vegetables and fruits can survive exposure to mild frosts, while others can tolerate and even thrive in harder frosts.
Plants Susceptible to Even Light Frosts
Here are a few of the common edibles that are susceptible to any frost
- Pole beans
- Dwarf beans
- Cucumbers, melons, pumpkins, and squashes
- Peppers and tomatoes
- Sweet potatoes
Plants Tolerant to Light Frosts (up to 32F)
Moderately hardy vegetables include:
- Potatoes (if they’re well-mulched or have a frost blanket)
- Leafy greens
- Cold-hardy pea varieties
- Chinese cabbage
Cold-Hardy Plants Tolerant to Hard Frosts (Up to 20F)
Cold-hardy vegetables are those that can tolerate hard frosts, which are sustained temperatures of 20F, and they include:
- Brassicas – kale, winter cabbage, cauliflower, broccoli, Brussels sprouts, romanesco
- Alliums – onions, garlic, leeks, salad onions
- Winter-hardy lettuce like lambs lettuce
What is frost?
Frost is the result of the air temperature falling below the freezing point of water. Your plants can be damaged by any type of frost – air frost, ground frost, or hoar frost. In plants, frost causes damage because it freezes the water in the plant’s roots or foliage which damages a plant’s tissues and prevents the movement of water and nutrients.
What plants should I cover in a freeze?
It depends on how hard you expect the freeze to be, how long you expect the freezing conditions to last, and what plants are growing. I’d always advise to be cautious and cover everything that’s at risk.
What temperature to cover plants?
What plants you’re growing and how hardy they are determines when you should cover your plants. As a general rule, you should cover tender plants and those that can only handle a mild frost if the temperature is set to dip below 32F. If it’s going to fall below 28F, I’d cover everything but the hardiest plants. And if it falls so -20F, cover everything.