Yes, keeping houseplants is considered a hobby, since a hobby is just an activity that you enjoy doing in your spare time for one’s enjoyment. Houseplants require care and attention, and many people enjoy talking to and tending to their plants in their spare time.
The houseplants hobby offers people an opportunity to nurture and care for something. The joy of keeping a plant alive and seeing it grow can be very relaxing, rewarding and is sometimes considered therapy.