Most houseplants are tropicals and prefer temperatures between 65-75°F during the day and about 10 degrees cooler at night. For many plants, temperatures below 50°F can cause problems.
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.
It should be noted that some house plants are more vulnerable to cold damage than others and when the thermometer dips – they can suffer. Some of those more sensitive to cold temperatures: Orchids (Phaleanopsis sp.), Mandevilla, Bougainvillea, Oriental Hibiscus, and Poinsettia.
If you're searching for a failproof plant that can thrive in the north or the south, in sun or in shade, in a garden bed or in a container garden, then the Persian shield is for you. This colorful, leafy plant is more than just durable, it's also a true standout in the garden.
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.
Perennials are a flower garden's backbone, providing beautiful color, texture and form. They are easy-care, dependable performers that come back every year. They also are: Uncommonly colorful thanks to foliage and/or flowers.
Alyssum. Alyssum is a warm zone perennial plant, which means it can bloom all year in climates like California. It has small, fragrant white, pink or purple flowers and grows best in full sun.
Evergreen flowering perennials will keep their green foliage all year, long after the blooming season is over. Many herbs are particularly known for being great practical flowering plants with evergreen foliage, such as Lavender, Rosemary, and Salvia, among others.
Agave Americana Blooms Once Every Hundred Years
It's also known as a century plant because it only blooms once every 100 years (roughly) and then dies. But, because Raleigh gets more rain than the plant's usual home in the high elevations of Northern Mexico, the Century Plant is blooming after only thirty years.
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.
The snowdrop flower.
As a plant that actually despises warm winters, the snowdrop flower performs its best in frigid temperatures. This flower can withstand temperatures down to -30 F. while still displaying its bright green stems and delicate, white flowers.
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.
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.
Annual Plants
Crabgrass, petunias, and snapdragons are types of annual that will not survive cold temperatures and will need to be cared for to survive winter.
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.
Moving houseplants outside is a big change in environmental conditions, so acclimating them is important. Never move houseplants from indoors into full sun. Leaf burn, discoloration, and drop can occur. On some species, especially succulents, the damage to the fleshy stems and leaves is permanent.
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!
Temperatures below 32 degrees can freeze the leaf tissue of cold-wimpy plants and turn them to mush after just a few hours. Some of the most tender annuals and veggies might not die but suffer cold-induced setbacks even when overnight lows dip below 40.
Welwitschia mirabilis: The world's toughest plant.