Dividing Lily Bulbs
"Some of our lily bulbs have been in the ground (undisturbed) for 3 years, and are quite large (about the size of a large grapefruit). Should they be divided before we re-plant them elsewhere?"
Unless you want them to be elsewhere, the bulbs would be just fine for another year or two in the same spot. Dig and divide when you see multiple stems emerging from the same bulb and the overall height of the stems are significantly shorter. Some springs may be warmer than usual and the bulbs could be naturally shorter that year, so do not worry about the lilies unless they have multiple stems emerging and seem crowded. During transplanting, if they have "split", you will see two distinct bulbs; simply pull them apart from one another.