Keep the temperature constant. Most indoor species of ferns are tropical, although not all require tropical weather. Make sure that the temperature in your home (or at least the room in which the fern is kept) is near 70 °F (21 °C).The ferns can handle temperatures as low as 60, but they won’t thrive as well under low temperature conditions.When in doubt, turn the temperature up. 1  Consider placing your fern in a bathroom; the temperature and humidity are often higher as a result of showers and baths.eep the temperature constant. Most indoor species of ferns are tropical, although not all require tropical weather. Make sure that the temperature in your home (or at least the room in which the fern is kept) is near 70 °F (21 °C).