Question
why don't some of my yucca plants bloom every year

Answer
Hi Rhonda,
Thanx for your question.  I think it depends upon the species of yucca.  Some do not bloom every year.  If you live in an area that gets cold a particularly cold or wet or otherwise severe winter can inhibit blooming.  The last factor has to do with how many nutrients the plant is getting.  If the soil is lean and not healthy the yucca can only save energy for a bloom.  It requires a lot of nutrition and energy for the plant to bloom.  I hope this helps.
Tom