Question
How often should this plant be waterd ? & why are the leaves at bottom of plant healthy , but leaves at top  are going crispy & brown , thank you

Answer
Hi Craig

Yuccas are watered every two to three weeks in summer and every four weeks through winter.

These are tough plants and are resilient to shade, heat and dry soil.

One reason why upper leaves crisp up is dry air. Keep it humid by spraying but also look for pest in the crown.

Another reason is that it is getting too much light or not enough food.

I think that the more possible reason for your plant is that it is not humid enough and the reason why the upper leaves are crisping is that they are more tender and need more humidity than the lower ones.

Look after it and it will recover.

Jonathan.