How many adults do you have? You need at least one of each sex for this to happen. Here in California you almost never see this... at least under P roebelleniis. All Phoenix can be pollinated by any other Phoenix species, so many of the naturally growing Phoenix here are hybrids... but for some reason, I rarely see P roebellenii have fertile seeds here. Just the bigger species. Congratulations.
I have three different multiples. I normally trim them severely in the spring to keep themmout of our way on thempool deck, so they don't look as full as they usually are in this pic. We are getting ready to have my daughters wedding in this area as the backdrop and these needed trimming and time to grow a bit before the wedding. I also usually cut off the seed stalks but sometimes they get away from me.
Thanks! I'm going to pot up a bunch this weekend and see how I do with them!