It could just be me, but I've had problems with yellowing plants and Miracle Gro. There's a lot of salt in it, and a lot of my houseplants resent that. I get yellowing and burned tips. Maybe cut back on how much you put in, and/or the time between treatments. If you only had the asparagus fern for two weeks, maybe it still had some fertilizer left in the soil that you bought it in, and got a bit overdosed. If that's so, then regular watering and time may be all that you need. You are likely, however, to lose the yellowed foliage. If the plant continues to grow though, then it should recover nicely in spite of the loss.
