Frost is one of a gardener’s worst foes! Learn how to predict frost, understand the difference between a frost advisory and a freeze warning, and protect your garden from frost!
What Is a Frost?
“Frost” refers to the layer of ice crystals that form when water vapor on plant matter condenses and freezes without first becoming dew.
- A light frost occurs when the nighttime temperature drops to at or just below 32°F (0°C).
- A hard freeze is a period of at least four consecutive hours of air temperatures that are below 28°F (–2°C).
Many plants can survive a brief frost, but very few can survive a hard freeze. (See more about this below.)
Frost Advisory vs. Freeze Warning
As with other significant weather events, meteorologists will often issue a “warning” or an “advisory,” depending on the likelihood of the event happening and its severity. According to the National Weather Service, the warning terms for frosts and freezes are defined as follows:
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Frost Advisory: Issued when minimum temperatures are expected to be between 33° and 36°F (0.5° and 2°C). Skies are generally clear and winds light.
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Freeze Watch: Issued when minimum temperatures are expected to be 32°F (0°C) or less within the next 24 to 36 hours.
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Freeze Warning: Issued when minimum temperatures are imminently expected to be 32°F (0°C) or less.
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Hard Freeze Warning: Issued when minimum temperatures are expected to be 28°F (–2°C) or less.
Of course, the easiest way to predict frost is to let the weatherman do it for you! However, if you want to be able to predict it yourself, read on.
Know Your Frost Dates
The first step in predicting frost involves getting to know the average frost dates for your area. Put your zip code in our Frost Dates Calculator to find frost dates for spring and fall for your location.
Note: These dates are averages, so they can only tell us what is typical. However, every year will be diffferent.
Also, the frost dates are based on a 30% probability, meaning that there is a 30% chance of a frost occurring after the given spring frost date or before the fall frost date. (In other words, these dates are NOT absolutes and should only be used as rough guidelines!)
Learn Your Microclimates
Keep in mind that the occurrence of frost can vary greatly by microclimate, too. In fact, while you may have frost in your garden, your neighbor across the street may see no sign of it!
A microclimate is exactly what it sounds like: a climate on a small scale. For example, if your garden is located at the bottom of a hill where cold air settles, it’s likely to be impacted by frost earlier than a garden at the top of the hill. Or, if your plants are abutting a rock wall in full sun, they’ll be kept warmer to some extent by the heat given off by the rocks.
5 Tips for Predicting Frost
Consider these factors when the radio and TV reports say “frost tonight”:
- Temperature: How warm was it during the day? It may sound simple, but one of the best ways of determining if a frost is due overnight is to gauge the temperature. If the temperature reached 75ºF (in the East or North) or 80ºF (in the desert Southwest), the chance of the mercury falling below 32ºF at night is slim. See our 7-day forecasts to check your weather forecast.
- Is it windy? A windy night is also likely to reduce the likelihood of a frost. A still night allows cold air to pool near the ground; a light breeze stirs things up; a heavy, cold wind sweeps away warm air near the ground.
- Is it cloudy? Observe the sky. If the Sun sets through a layer of thickening clouds, the clouds will slow radiational cooling and help stave off a frost. With clouds, the risk of frost is reduced.
- Slope: How is your garden landscaped? Gardens on slopes or high ground often survive. However, cold air sinks and will puddle down into the valleys and hollows. If your home and garden are at the bottom of a slope or in a valley, and there is no wind, then there is higher risk of frost. A landscape with trees can assist in preventing frost. Trees transpire a lot of moisture through their leaves.
- What is the dew point? As a rule of thumb, don’t worry about a frost if the dew point (the temperature at which the air is no longer able to ‘hold’ all the moisture within it) is above 45°F on the evening weather report. The more moisture in the air, the less likely a frost. A light watering of the garden a day or two before a frost is predicted can help stop it settling.
What Temperatures Cause Frost Damage?
Frost causes damage and even failure to many vegetable crops. But also there are other vegetables which actually benefit from a frost. The flavor of broccoli, for instance, actually improves if the plant has experienced a frost, and carrots get sweeter as the temperature drops.
How low can you go? The temperatures shown in the graphic below tell you when the frost will cause damage to the respective vegetable.
How to Protect Plants from Frost
Frost can hit in spring or fall in most areas. Generally, covering plants to create a temporary pocket of warmer air is the best way to protect them.
- Keep an eye on the weather forecast. If it looks like temperatures are going to drop, get ready to protect tender plants.
- Make use of season extenders like row covers, cold frames, or cloches to protect tender plants, such as seedlings or warm-weather veggies. Row covers or garden fleece can be used to help create a warmer environment beneath them. You’ll need to use posts, bamboo, or flexible PVC piping to create space for the plants to grow, then drape landscape fabric or plastic over the frame; weigh down the edges with rocks or bricks or pegs so the covers do not blow away. To protect young plants from frost, use 2-liter soda bottles cut in half as cloches.
- It’s best to have all covers in place well before sunset. Drape loosely to allow for air circulation. Before you cover the plants in late afternoon or early evening, water your plants lightly.
- Remove any covers by mid-morning so that plants can get full exposure to the warming sunlight.
For more frost protection tips, read our main article: Protecting Your Garden from Frost.
Learn More
Following these tips should help prevent your garden from taking too much of a hit when frost occurs!
For even more end-of-season gardening advice, see Preparing Your Garden for Winter and Fall Chores: Autumn Garden Cleanup.
Let us know in the comments what you do to prepare for frost!
Reader Comments
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wrong word
Mulch to keep ground from freezing not thawing
First frost
I've been told that here in middle Vermont that if the temperature at 9 PM was 40 degrees or less, there would be a frost by morning. So far, that's worked for me. If I cover my remaining tender plants that night, can usually get another week or two 'fore I have to harvest them.
Preventing frost
If you can part your car or truck next to your garden, the frost will be absorbed by it, and a light frost will be avoided. The metal of a vehicle seems particularly attracted to frost, but a hay wagon or other large object is helpful too.
let us know when they put it
let us know when they put it on new for frost
Leeks can survive a hard
Leeks can survive a hard frost? Wow! This my first year planting them and I did not know that. I'm glad to hear it, because I was a little late getting them in and our average first frost is only 5 weeks from now.
Thanks for the information, Catherine.
What kind of mulch can I use on the parsnips?
Paul
Brunswick, ME
Compost, straw or chopped
Compost, straw or chopped leaves are all good mulches for root veggies.
My family folk lore has
My family folk lore has passed down the theory that the day you first hear a cicada, you have 15 weeks until your first frost. we live just south of the Boston area, so the weeks will vary for your locations.
Last year my husband was one day off, and i was a week off. This year i was on the exact day of our first frost and my husband was a week off. Pretty good for folk lore.
For us here in Tampa Fla
For us here in Tampa Fla anything close to a frost or freeze will cause damage. Most if not all landscaping is grown in south Fla then shipped up to us. Tropical plants just will not handle cold temps. In a "normal year" we get two maybe three cold nights a winter. Last year we had ten days in a row of hard freeze. Is this our new "normal?"
first HARD freeze was last
first HARD freeze was last night, November 1st temps dipped down to 31
We had our first frost last
We had our first frost last night, Oct. 3, in central Arkansas. May do it again tonight. Very early this year.
My farmer grandfather said
My farmer grandfather said frosts generally come on or after the full moon, which pulls in high air pressure from the north-west.
That's amazing, Sil. I'd love
That's amazing, Sil. I'd love to hear more of what your grandfather told you about gardening.
As of Sept 30, 2010, we still
As of Sept 30, 2010, we still haven't had frost in my town of Dublin, NH! I will say that I didn't grow regular tomatoes again this year. Instead I grew cherry tomatoes--almost all ripened up! It was a nice long season. Hope you had some gardening successes!
Tomatoes in British Columbia.
Tomatoes in British Columbia. I uprooted my Gardeners Delight cherry tomatoes from my balcony just before our cold snap in September. (Now it's warm again). I picked off the leaves, and hung whole plants upside down to dry indoors. The tomatoes ripen a few at a time making a nice fresh snack. The tiniest will be too small to fry, but provide bright colour contrast in the arrangement! Perhaps they will make a spooky Halloween decoration for my door!
Here in Calais, ME we have
Here in Calais, ME we have had 2 or 3 frosts since late September. However, no hard frost as yet. It was a terrible year in the garden due to above average rain early on and cool temps all summer...no tomatoes to speak of this year. I have never taken to fried green tomatoes, but do like green tomato mincemeat etc..so all is not lost I guess.
We here on the shores of
We here on the shores of Oneida Lake have escaped a frost ,while others inland have had one.The unfrozen lake gives us a bit of insulation since the water holds some warmth.But watch out after it freezes,then it acts like a giant ICE CUBE!
Folklore says if we in LA
Folklore says if we in LA have fog in August we can expect frost on that same day in October, we had no fog in August so now I'm not sure! But, usually it is anywhere from mid to late Oct. when we get our first frost. Our garden has long given up it's bounty except for my sweet potatos and I'm told they need to be harvested when the leaves turn yellow or after the first frost. Seems they are much sweeter after it has frosted on them, so I shall wait for frost before harvesting them.
Our first frost in upstate
Our first frost in upstate New York usually comes anywhere from mid-to late September, and it did so last Friday night (18th). Now we can go and pick apples this coming weekend because the frost will have made them even sweeter! I covered my container tomato plants with plastic because I didn't want to harvest all the fruit just yet, since we're having much warmer weather this week (but not so much sun). I make it so that each container becomes its own little greenhouse. I should be able to prolong their season on the vines into October.
The first frost in Prince
The first frost in Prince Albert SK Canada is about the 4Th of Sept. This year the temp has been at a record level and seems more like August than Sept with Temperatures reaching 28 and 29 celsius. As of the 22 of Sept there has been no frost and no temperatures even close and it looks like there will be no frost until Oct. What a great fall.
The first frost in Indiana
The first frost in Indiana usually doesn't arrive until mid or late October. Before that, I snip my herbs, mince them, and put them in plastic containers in the freezer. They make wonderful fresh herb additions to soups and stews! Or you can simply cut down the entire herb plant, hang it upside down in a cool place, and use the herbs dried. I harvest my green tomatoes before the frost and put them in a brown bag on the kitchen counter. They will eventually ripen. However, check them frequently as sometimes they are too green and will never ripen. Then you can use them for fried green tomatoes!