The common advice on yucca in my area (Kansas) is that the only way you're likely to harm one you want to keep (outdoors in the ground) is by watering too much. If the roots and crown don't get a chance to dry out pretty well they may "rot" - which usually is due to fungus/mildew growth.

Naturally the previous owners of our place planted a couple of them immediately adjacent to a couple of river birch trees that require massive and constant amounts of water. We've tried very hard to keep the birch trees wet enough, with only moderate success; but thus far the yuccas haven't seemed to mind.

"Benign neglect" is the recommended management method, and one may omit the "benign" in most cases, for yucca planted in the ground with reasonably good drainage.

Potted yucca are a little more difficult, since the pot may hold too much water for too long when you water, and pots tend to dry out a little too much even for yucca if you ignore them for long periods. It's also difficult to find pots that accomodate the very long taproot, so they tend to quickly become "root bound." For those who for some reason feel the need to have potted yucca, the usual recommendation is "replace as needed."

John