Can we assume you had the Asparagus ferns in the shade (bright indirect light) outdoors where they thrive best?
Indoors, place the Asparagus fern in a bright location. A few hours of winter sunshine is good (direct summer sun can burn leaves). Unfortunately, as the plant
adjust to the lower light of your home (light in even the brightest window is many times less than outdoor light)you can expect the plant
to shed many, if not most of its sharp leaves. New leaves that are acclimated to the indoor light will eventually replace the shed leaves. Give it time.
Or, if you don't like the apprearance of sparse growth or picking up shedding leaves - did I mention they are SHARP?! - you can prune the plant
back to any length up to an inch above the soil. It won't hurt the plant
and new growth will be lush and full, especially if you regularly prune extra long or dead stems.
Let the top 1/2 inch of soil dry out between waterings, then water thoroughly.
Asparagus ferns are fast growing
with exceptionally strong tubers but they do well rootbound. Some well-established older rootbound plants
produce red berries in early spring
Best of luck.