Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation. Severe or hard freeze - 25° Fahrenheit and colder causes heavy damage to most plants.
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.
WHEN TO BRING PLANTS INSIDE. As a general rule, tender plants should be brought in when nighttime temperatures are below 50 to 55 degrees F, even if they are hardy for your zone. A plant's roots are more exposed when planted in a container versus in the ground.
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.
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.
Water only when air temperatures are above 40 degrees F. Apply water at mid-day so there is time to soak in before possible freezing at night. A solid layer (persisting for more than a month) of ice on lawns can cause suffocation or result in matting of the grass. Newly planted shrubs will require more winter water.
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.
So even though the weather forecaster isn't predicting a freeze, once temperatures start to drop below 40°F you need to be aware. 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.
You'll be able to tell when your garden is suffering after a cold snap. Leaves will curl, drop, or change color — usually from a green to a white, yellow, black, or brown.
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.
If it stays cold for more than one night, can I keep my plants covered, or should I remove the coverings at some point? A. Our recommendation would be to remove the cold protection covering once temperatures are above 32 degrees.
Light freeze - 29° to 32° Fahrenheit will kill tender plants.
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.
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.
Some plants can survive outside even when temperatures hit freezing. Others need to be brought indoors when temperatures reach the mid-40s. Be sure you know this before you plant.
Hardy plants can be hardened off when the outside temperature is consistently above 40° F. Half-Hardy plants may be hardened off at 45° F.
Second, know that a light frost—32°F and colder—kills all tender plants such as tomatoes. Hardier plants such as spinach and kale will survive until there's a hard freeze—28°F and colder.
It depends on the temperature, and specifically the nighttime low temperatures. You'll want to move your houseplants indoors before night temperatures get below 45°F. Any colder, and you're likely to see damage, especially on tender new leaves and stem tips.
Low Temperatures: The signs of cold damage can be confusing, since some damage may not be evident until months later. Leaves and tender shoots subjected to freezing temperatures or chilling damage appear water-soaked and wilted. These tissues will usually turn black within a few hours or days.
The general rule of thumb is that most plants freeze when temperatures remain at 28°F for five hours. Of course, there are exceptions to this rule. Seedlings, with their tender new leaves, often give up the ghost when temperatures dip to 32-33°F. Tropical plants have differing low-temperature thresholds.
From that experience, I've found the best frost protection for your outdoor plants is either free or cheap. Cardboard boxes and brown grocery sacks make perfect frost cover and at the end of the season can be recycled. I keep various boxes on the patio and when frost is forecast simply put one over the plant.
In fact, you can leave plants covered with blankets or sheets for several days without harming them if freezes are likely for several nights in a row. But eventually the covers must be removed so the plants can get light.
Most houseplants are tropical plants that can safely grow in a heated home during the winter. They will never survive outdoors in winter unless you live where the temperature stays at least above 50 degrees. In northern zones 4 and 5, plants need to survive months of below freezing weather every winter.
You should cover plants until temperatures are back into the upper 40's to 50's. If it looks like a couple of days of cold temps, leave the coverings on for a couple of days.