For flowers in general, light is the number one determining factor as to whether or not they bloom, especially when the foilage looks healthy otherwise. Sometimes too much fertilizer will cause a problem with excess green growth at the expense of flowers, but I doubt that is the case with this indoor plant. My wife was given an amaryllis three seasons ago, each year the bloom has gotten bigger and better. This year it made two flower spikes, one having five flowers and the other having four. Each year the plant is left outside until a killing frost kills the top growth back. The bulb is then repotted into fresh potting mix, with about 20% extra perlite to help with drainage and avoid root rot. The plant is lightly watered about once per month during the winter. In the spring the plant shoots up a bloom which is enjoyed in the house. Then after all danger of frost is over, we fertilize with a balanced slow release fertilizer and set the plant outside in filtered light under an oak tree. The plant sits there growing its lush green leaves and storing energy for the next bloom until the killing frost comes and it is time to repot and move the plant inside again. We now have three amaryllis that have been through this process for one or more season, all of which bloom vigorously each year. The only change that I may make is to start adding a bit of super phosphate at repotting time, but then when some isn't broke.......
Here is a photo of that first plant my wife got. It is in full bloom now and its the best bloom ever.
Eclectic gardening style, drawing from 45 years of interest and experience. Mostly plant in raised beds and containers primarily using intensive gardening techniques.