I have purchased iris that say they are reblooming. Why don’t they rebloom in the fall?
There is a wealth of interest in reblooming iris. The traditional iris blooms only once, in the spring, and goes into summer dormancy. Hybridizers continue to work on iris that bloom multiple times during the year. Most rebloomers bloom in the spring and then again in summer or fall. There is even a group called “everbloomers” because they bloom constantly, until frost, if the conditions are right.
Rebloomers are almost as easy to grow as the ordinary iris. They need well-drained soil and to be fertilized in spring as well as after the spring bloom with a fertilizer that is fairly low in nitrogen such as a 5-10-5 mixed 50/50 with superphosphate. You don’t want them to go into dormancy after blooming the first time, so continue to water during dry weather. Ordinary iris can be planted under shade trees because they only need sun before they bloom in the spring. Rebloomers need at least a half day of sun all year. These reblooming varieties are said to be more resistant to rot, more vigorous in growth, with less spot and insect damage.
As fall approaches, cut off all flower stalks with buds and bring them indoors. Cut the remaining foliage to the ground. Uncut stalks usually freeze and fall over, causing rot. These reblooming iris increase faster than the standard iris and may need to be divided every second or third year.