Certified GKH Gardening Expert
Yellowing of the bottom (older leaves) is generally ok provided that the remainder of the plant is thriving. Simply keep doing as you are and remove the old, yellowing foliage (carefully, these may still be sharp). Occasionally, this can be attributed to an over abundance of moisture or even a nutrient deficiency, but typically these plants rarely become affected by anything too serious. Water the plant only when the soil is dry to the touch.