Do you know which Asparagus Fern you have?
Here in Florida the Asparagus sprengeri:
Asparagus Fern (Asparagus densiflorus 'Sprengeri') is an extremely noxious weed, almost impossible to kill. I've never fertilized the Sprengeri's in my yard and you can see from the photo's in the database that they are quite large and healthy. I don't think anything can kill these things! The needles sometimes yellow and fall when the plants get too dry. Over fertilization can also cause yellowing and dropping of foliage.
Your plant may perhaps be responding to the fertilizer, the cool temperatures in the room it's located, or it could be a moisture issue. If it's root bound to the point where the water is running right through it will need a larger pot.
