Question
What would an ideal humidity for a Boston Fern be?

Answer
Billy Bob
Ideal humidity for a Boston-fern would depend on numerous factors - location (indoors/outdoors), lighting (sunlight/artificial), etc. They don't like direct sunlight but will tolerate morning sun. You can increase humidity by spray misting the foliage periodically or putting the pot on a saucer filled with rocks and water.
Proper watering is more important than the amount of humidity. Water your plant based on how much it weighs when thoroughly watered VS when it is ready to be watered again. Plants die from too frequent waterings (or going too long in between waterings), not from how much water you give them at one time. Pick the pot up and feel how heavy it is after watering it thoroughly. Don't water it again until it feels considerably lighter and the top of the soil is lighter in color. Depending on plant types, sunlight exposure and pot size plants will need water at many different rates from once a day to once a month or more.
Get to a local garden center and buy a good fern fertilizer. Ask them which fertilizer they recommend and read the directions before applying it...Plants do need to be fertilized periodically to stay healthy...

Hope this helps.
Rick in southern NJ