They have been growing in the same spot for about 10 years.

This is what I discovered.

It takes a season or two for the bulbs to get established, and for you to see hopefully 12 blooms.
Those bulbs will multiply by growing, and then the bulb dividing/splitting, making 2 bulbs. They are much like any other bulb, that in time, there will be fewer and fewer blooms because they have grown too crowded. I'd suggest once they are finished blooming, and the flower stalk has dried somewhat, digging and dividing them up, so they won't be crowded.

I tend to try and do things when I have the time, and am thinking of it, so I don't know for sure what might be the best time for digging and dividing, and resetting them. Maybe someone else here has some input on that.

Sue

I'd second that opinion, and I'm glad you asked.

I noticed this week that I have only 3 stalks from my plants. My situation may be exacerbated a little by the fact that the peonies and other plants I put in at the same time have really taken off, and there's more competition for light and water when it comes time for the flowers to bloom -- I certainly get a ton of leaves in the spring.

I would imagine early fall, once it cools off a bit, would be a good time to separate and transplant the bulbs. You might even get flowers next year if they have the fall and winter to adjust.