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.
One way or another, when a warm spell during winter is forecast to be followed by a cold snap, make sure to protect not only the pot and the roots but also the top of the plant. Cover plants with plastic film, burlap, blankets or other cloth material at night.
If low temperatures loom, cover plants with cloth, burlap or plastic at night. If you use plastic, be sure to remove the covering during the day since temperatures can heat up, causing premature bud growth. Also, when covering, avoid damaging the top part of the plants.
Know Your Plants' Cold Tolerance
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. You'll need to look up each of your plants to verify its cold tolerance.
Plastic can be used to protect plants from frost, but it's not the best or most effective material. In fact, the horticultural experts here at Green Impressions actually recommend against it. Plastic materials such as vinyl and traditional camping tarps aren't breathable, causing moisture to get trapped inside.
A fabric covering is best because it will allow moisture to escape while still protecting your plants from frost. Fabric coverings will prevent the freezing air from coming into direct contact with the moisture on the plant while also capturing the heat that is radiating from the ground.
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.
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.
Cover them during the cold hours of night. During the day, the soil absorbs the heat from the sun. By covering plants in the evening, the covering captures the heat the the soil re-radiates out into the night.
Plants to move inside: Tomatoes, peppers, eggplant and others that will not survive frost. Plants to cover: Potatoes, radishes, spinach, leaf lettuce, beets, mustard. Plants that do not need to be covered: Onions, cabbage, broccoli, cauliflower, carrots, turnips, kale.
When not in use, during the winter months we recommend that the pot is emptied, cleaned and stored ready for further use the following season. It is our view that terracotta pots are not 100% frost proof, nor for that matter are other similar materials such as concrete or cast iron.
If it is not going to rain before the freezing temperatures arrive, you should water plants thoroughly. This is because moist ground stays warmer than dry ground. Watering the night before the freeze arrives will insulate the root structure of the grass and plants, decreasing the potential for cold injury.
While some plants can survive light frosts, others will die as soon as their cells freeze. Depending on their hardiness, some potted plants will respond to the first frost by going dormant just like garden plants do. However, as the temperature continues to drop, their roots might die unless they are protected.
A frost blanket is a sheet of fabric, plastic, or other material used to cover plants in cold. There are different types of frost blanket, some designed to protect crops, others designed to shield plants in a home garden.
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. Well, we have temperatures forecast to dip into the 40s again on Thursday and lower 40s on Friday.
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.
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.
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.
40 to 50 degrees can cause death in one to three hours. 32 to 40 degrees can cause death in 30 to 90 minutes. 32 degrees or less can cause death in as little as 15 to 45 minutes.
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.
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.
A local study done on frost formation relating temperature to dew point has these guidelines for frost: temperatures from 38 to 42 F can lead to patchy frost, 33 to 37 areas of frost, and 32 and below widespread frost/freeze.
The best type of frost protection is frost cloth, which is a breathable fabric because it can 'breathe,' you can leave the frost cloth on your plants for a longer period. But, use it only when there is a threat of frost. After three days, uncover your plants during the day to allow the sun to reach your plants.