My pond was installed in June '04. At that time, the pond company planted some marginal plants for me - including some Iris plants. When they put them in, they were about 8-10 inches tall - without blooms.

Just now, ONE of the 4 iris plants bloomed. The others dont show any signs of producing flowers yet.

How old does an Iris plant need to be in order to bloom?

I repot my iris in September. I've found that the following spring, those that were repotted rarely produce flowers or very few. By the next spring, they do pretty good. After that, they produce fewer as they become root bound unless they jump the pot and grow wild; then, all bets are off as it's iris city! I repot some iris in my 153 gallon pond in March, and they don't bloom. I have to repot them due to a confined space. The larger the pot you can provide, the more likely you are to get flowers. They also like being free-growing in gravel or even just from a pot jump with their roots in the water. Certain varieties flower more readily. The more delicate iris produce just a flower or two a year while the same size plant of yellow flag iris will produce a dozen flowers.

There is a difference between the age of the iris (the rhizome) and when it was potted up. By that, I mean you can pot up a 1-year-old rhizome, and it may take a few years to bloom while a large chunk of 10-year-old rhizome even if freshly repotted, may bloom right away. I've had yellow flag iris that set themselves from seed bloom about the second year after I saw leaves but they are almost a different plant because they grow so easily and fast and big compared to my other water iris.