In general, foliage plants grow best between 70 degrees and 80 degrees F. during the day and between 60 degrees to 68 degrees F. at night. Most flowering plants prefer the same daytime temperature range, but grow best when nighttime temperatures range from 55 degrees to 60 degrees F.
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.
For many plants, temperatures below 50°F can cause problems. Adjust thermostats to cater to your comfort, but remember your plants need some consideration. Avoid placing plants near cold drafts or heat sources. Keep plants several inches away from exterior windows.
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.
Like all living things, houseplants have specific temperature requirements. In order for them to survive and thrive, these must be met. Most plants prefer a temperature of no less than 60° F, though many can tolerate as low as 40° F.
It's safe to move your plants outside when the outdoor temperatures stay consistently above 50°F. Pay attention to the weather report. If nighttime temperatures are set to fall below 50°F, bring your plants in for the night.
Most plants: You will find most house plants grow at their best between temperatures of 60 – 75°F (15 – 24°). Some (not many) need less and other's need slightly more, but plants that grow well within this range are well suited for homes and offices (because many rooms are kept close to these temperatures, already).
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
Check the water needs of plants after a freeze. Water that is still in the soil may be frozen and unavailable to the roots and plants can dry out. To make sure a plant is getting its needed water, apply water to thaw the soil and the ice.
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.
Add a Thick Layer of Mulch
Just like slipping on a sweater when it's chilly, adding a layer of mulch to your garden beds will help protect the soil from sudden swings in temperature. Use straw, wood chips, leaf mold, or even just a heap of leaves to provide crucial insulation for the plants' root systems below ground.
It's important to pay attention to the temperature dropping when the sun goes down. Once temperatures are consistently between 60 and 45 degrees Fahrenheit, it's a good idea to start bringing your plants inside at night. However, you can keep them out during the daylight hours if the temperature stays above 45 degrees.
Most flowering plants prefer the same daytime temperature range, but grow best when nighttime temperatures range from 55 degrees to 60 degrees F. Lower nighttime temperatures help the plant: recover from moisture loss, intensify flower color and prolong flower life.
Use a frost blanket, cloche or row cover material – not plastic — to insulate the ground around your outdoor plants and keep them warm. Prop the cover with sticks or stakes to keep it from coming into direct contact with the new growth. And, make sure to remove the cover the next morning after the temperature warms up.
The easiest way to harden transplants is to place them outside in a shaded, protected spot on warm days, bringing them in at night. Each day, increase the amount of sunlight the transplants receive. Don't put tender seedlings outdoors on windy days or when temperatures are below 45° F.
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.
Evening watering gives plenty of time for the water to penetrate the soil and for the plant to take it up, but there is a concern that leaves staying damp overnight will provide access to disease.
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.
Try not to water at night. Night-time watering is not ideal because your plants' leaves may not be able to dry off as quickly as other times of day. Wet leaves are more susceptible to diseases. That said, water your plants the moment you notice they look wilted.
Use water that is about room temperature to avoid shocking the plant's roots. Tap water can get very cold in some winter climates, so let the water sit for several hours before watering your plants. Gradual warming in this way also allows dissolved gases, such as chlorine, to evaporate out of the water.
When To Stop Watering Plants in Fall. When the air and soil temperatures consistently fall below 40 F, it's time to stop watering. The ground can't absorb water once the top few inches freeze. Continue to water your plants up until this point so they're as well-hydrated as possible going into winter.
It has to do with the relative humidity. A higher indoor relative humidity makes the 68 degree temperature feel more comfortable; a low relative humidity makes it feel chilly.
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.
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.