Once temperatures drop below 40°F, you may want to start covering your plants with a frost blanket depending on what you're growing, which we'll get into in just a bit. Freeze – A freeze is when the air temperature is 32°F or below.
As gardeners, our frost dates are based on 32 degrees Fahrenheit (0 degrees Celsius) to avoid the risk of any plant death. However, know that even if air temperatures are as high as 38°F, frosts may occur on the ground and on plants. It's better to protect plants just in case!
To know when to cover your plants, you need to know when the plants you have are susceptible to frost damage. Some frost-tender plants need to be covered as soon as the temperature hits 32°F, while others can handle lower temperatures and/or longer freezing periods.
I did some research and found out that houseplants need to be taken indoors before overnight temperatures dip below 45 degrees. Most tropical plants suffer harm from temperatures below 40 degrees.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants. Cover plants before dark to trap warmer air.
Frost Advisory - This is when the temperature is expected to fall to 36 degrees to 32 degrees Fahrenheit. Freeze Warning - This is issued when there is at least an 80% chance that the temperature will hit 32 degrees Fahrenheit or lower. Light freeze - 29° to 32° Fahrenheit will kill tender plants.
When Should You Cover Plants? Cover your plants at night and remove them during the day when the temperatures rise above 32 degrees F, so that the soil can warm up again. Some outdoor plants won't survive the harsh conditions of winter, bring them inside and use these tips for caring for them through winter.
Once temperatures drop below 40°F, you may want to start covering your plants with a frost blanket depending on what you're growing, which we'll get into in just a bit.
Signs Your Plants May Be Too Cold
The leaves brown and fall off. If your plant is too cold, it may begin to die, and its leaves will brown and fall off. The leaves turn yellow.
The easiest way to protect from a freeze is simply by covering plants with a sheet or a blanket. This acts like insulation, keeping warm air from the ground around the plant. The added warmth may be enough to keep a plant from freezing during a short cold snap.
Time It Right
While it might be tempting to ship indoor plants outside at the first sign of spring, it's best to wait until nighttime temperatures stay at or above 60°F, and after any threat of frost has passed. If you're planning ahead, use the average last frost date for your area as your guide.
Should I cover my plants at 36 degrees? As a whole, all tender plants should be brought indoors or protected with garden fabric to prevent frost when it is 36°F outside. For cold-hardy plants, this is entirely optional. But it's better to err on the side of caution when the temperature falls below 40°F.
A frost can occur anytime temperatures drop to 37° or lower. Most often, frosts are associated with clear skies and calm winds overnight and during the early morning hours on a cold day. On the other hand, a freeze only occurs when surface temperatures drop below 32°, or the point at which liquid water freezes.
Here's a quick summary: Between 36 and 29 degrees, your most vulnerable flowers are your “tender annuals.” Tender annuals are your one-season flowers that like warm air and warm soil to grow. They like having “warm feet,” meaning they want their roots to be comfortably warm.
Yes – if you secure the plant properly. Garbage bags work to cover plants and protect from frost, but they must not be allowed to touch the plant's surface. Use stakes and supports to create a tent-like structure over the plant, which will retain warm air. Make sure the trash bag goes all the way to the ground.
A covered porch usually provides protection from light frost, but the garage or sun room is better for freezing temperatures. A couple days in darkness won't hurt the plant. Or move them out during the day and back in at night, if cold temperatures persist.
When should I wrap my plants for winter? This Old House landscape contractor Roger Cook suggests to start wrapping your plants in November. If your plants are new, be sure to cover them for the first two years. The older your plants get, the sturdier they become in surviving winters.
Semi-hardy cool-season crops (beets, carrots, Swiss chard, lettuce, cauliflower, potatoes, parsley) grow in minimum daytime temperatures of 40 degrees and higher. They cannot withstand hard frost without some kind of covering or protection.
Thoroughly Water plants if it's not going to rain before the freezing temperatures arrive. It may sound illogical. However, a moist ground stays warmer than dry soil. Watering the night before the freeze comes will insulate the root structure of the grass and plants and decreases the potential for cold injury.
Indeed, a plant that is drought stressed will often show more damage after a light freeze. So if they are dry, always be sure to water your potted plants before a freeze to help them better handle the cold.
It is best to water in the afternoon or evening the day after a freeze so plants have had a chance to slowly raise their temperature. After a freeze, soft-stemmed, non-woody plants such as impatiens, cannas, elephant ears, agapanthus, amaryllis, begonias, philodendron and gingers may be pruned back to living tissue.
If you're wondering at what temperature threshold you should be bringing your plants, there's a short answer: when nighttime temperatures reach 45 degrees (F), it's time to bring your plants indoors.
The National Weather Service (NWS) says that a frost can form when the temperature falls below 36 degrees Fahrenheit, with it being more than likely in rural areas. Frost becomes more widespread when the temperature falls below 32 degrees.
It's important to keep an eye on the weather – specifically the night ranges – and ensure that your green friends are never outdoors in degrees lower than 45 degrees. If you care for tropical plants, anything lower than 40 degrees will cause severe harm.