Answer: I'm not sure trying to reduce the size of your century plant is a do it yourself project. In addition to the sharp spines at the ends of the leaves, there are dozens of spines along the edges of each leaf. This makes for a trechorus situation. I suppose you could carefully snip off each spine from the leaves you want to remove and then cut them at the base using a folding tree saw. They are easy to handle and quite sharp. You can reduce the size of the plant by removing some of the leaves, but you can't really shorten the leaves and have them survive, nor can you lop the top off the plant the way you might do with a shrub or a tree that's gotten too large. It may be that you'll need to have the yucca removed completely and this is a job for a professional. Wish I could offer more suggestions.
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