Boston Fern Care. Keep the soil damp. If the soil becomes dry, the fern plants die out. Therefore, make sure you water the plant as and when the soil seems dry. You can even soak the Boston fern plant pot once a month. Another aspect of Boston Fern Care is fertilizing. You need to add a balanced 10-10-10 water-soluble liquid houseplant fertilizer to the plant just a few times in a year. They do not need a lot of fertilizer for their growth.