@yardenman. Hello there. I'm sorry. I can't answer the question you have for the mulch and tulips. I have no experience with tulips.
To answer your lily question. Some flowers multiply faster than others. What most people do is when the flower count seems to not be as good, poor performance than previous years, then it's time to dig and divide.
Others will just dig and divide every 3 years or so. How long have you had them planted in this container?
