I have predominantly blue irises in my yard. Some years ago, to my delight, some tall yellow irises appeared. They disappeared after two seasons. Now, more than 5 years later, three stunted, 8″ tall, pure yellow irises appear 3 ft from the original iris cluster. What do you think could have happened? (I had a similar situation of disappearing white iris in the back yard. It never showed up again.)
My guess: seeds from a seed pod got blown to the site, and it took several years for the seeds to germinate.
Thank you for contacting the Toronto Master Gardeners.
Irises can be easily propagated from seed. If you don’t deadhead your Irises immediately after blooming they form a triloculed seed pod which splits open once the seeds are ripe. If the seeds find themselves in a favourable place in your garden you will see grass-like seedlings in the spring. According to the American Iris Society: “Even if the requirements above are met, not all the seeds will sprout the first year. With garden variety bearded irises, the percentage will usually be more than 50%, and can approach 100%. Most of the remainder will sprout the following year. At the other extreme, aril irises may sprout a few at a time over a period of 10 years or more. Why is this? It is nature’s “insurance policy” against calamities and harsh conditions of various sorts. If all seeds sprouted at the same time, a drought, flood, fire, or other disaster could destroy the whole population. By having the seeds sprout over the course of several years, it is virtually guaranteed that some will survive.” This is why you are seeing Irises coming up over a number of years.
Most Irises are hybrids and do not breed true, as a result the new Iris will probably not be the same color as the mother plant. Which is exactly what you are seeing. Who knows, you may even have a unique Iris!
If you are interested in germinating Iris seeds this article gives specific instructions.