Most houseplants enjoy the same temperatures we live in. If you feel comfortable with the air temperature - your plants probably will too.
Relative humidity is another matter all together. In the winter, when central heating takes over, houseplants struggle because the air tends to be extremely dry. Indoor plants are tropical creatures and suffer when humidity levels drop.
Most indoor plants are happy with the same temperatures we live in.
It's easy to feel the temperature in a room by simply standing in it. Understanding temperatures from a plant's perspective isn't that simple however.
Temperatures in a typical room can vary a lot. Some windows get more sun than others. The effects of heat or air conditioning in the room also vary. Each of these spaces are called "micro-climates".
For example, the temperature close to a window can be much different than the temperature in the middle of the room. When the weather outside drops below freezing in winter, the temperature at your windowsill could be in the 40's. On a hot summer's day the temperature at that same window can soar to 120 degrees - or more!
A good way to identify micro-climates in your home is with a "minimum/maximum" thermometer. It not only shows the current temperature and humidity, they also record the highest and lowest temperatures and humidity levels over time. I use them all the time.
"You'll become a better grower when you start measuring instead of guessing."
Humidity is moisture in the air. Most indoor plants come from the tropics and they need humidity. The ideal humidity range for indoor plants is in the 40-70% range.
Providing adequate humidity can be a challenge in winter.
Humidity levels are closely tied to air temperature. To help maintain higher humidity during the winter, turn down the thermostat. Your plants will gladly trade cooler temperatures for the hot, dry air from the furnace. Don't worry about your plants getting cold - you'll be chilly long before your plants will.
In the summer, air conditioners not only cool the air, they also remove moisture, which lowers the humidity. Plants hate cold drafts from air conditioning!
Grower Tip: Don't confuse humidity (moisture in the air) with water in the pot. Watering your plant more to compensate for dry air is a sure way to kill it.
1) Lower room temperatures. Cool air holds moisture better than warm air. As long as the root zone stays warm, air temperature can go as low as 60 degrees.
2) Put your plant(s) on Humidity Trays. Moisture in the air increases as water in the tray evaporates.
3) Invest in a humidifier.
Unfortunately, misting plants to increase humidity doesn't do much. The effects of misting are short lived. Unless you mist your plant every 30 minutes - around the clock - misting won't help.