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.
Most plants prefer a temperature of no less than 60° F, though many can tolerate as low as 40° F. Along with this, while the improper temperature can certainly be an issue, fluctuations in temperature are the true killer. Learn the ideal temperatures for your green friends so they can be healthier and happier.
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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.
Remember to protect electrical connections from moisture. 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.
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.
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.
Luckily for gardeners in mild-winter regions (the warmer parts of Zone 8 and south), container-grown plants require little or no winterizing beyond moving pots to more sheltered locations and perhaps covering them with frost blankets when freezing temperatures are expected.
In warmer zones, the winter planting window is wide open. You can sow seeds for winter vegetable crops, like salad greens, radishes, carrots, onions, Swiss chard, English peas and kale. Look for transplants of other cool-season vegetables, including Brussels sprouts, broccoli and cauliflower.
Leaves Wilt or Droop — As the cell damage occurs, the leaves will lose their rigidity and start to droop or even curl in on themselves. If you have been watering as usual, it is time to consider other causes for your plants' wilting and drooping appearance including cold shock.
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.
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.
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.
Viola, winter jasmine, calendulas, and many plants love cooler temperatures, and they don't hesitate to take advantage of winter's pollinators. Plants like black-eyed Susans and lavender won't be making an appearance in winter. They prefer the warm weather of summer.
Welwitschia mirabilis: The world's toughest plant.