I would appreciate advice about how to make my reblooming irises rebloom. They did not rebloom last year. Spring blooming is finished.
Firstly, reblooming irises (remondtants or repeaters) are not guaranteed to preform as promised. But there are several things that you can do to encourage them to rebloom in the late summer early fall. These irises have a rapid growth spurt after the first blooming sending up new bloom stocks several weeks after the first blooming period. Therefore feeding with compost and composted manure, together with a sprinkle of low nitrogen chemical fertilizer after the first blooming is warranted . Do not cover the rhizomes with compost or let fertilizer come in contact with them. Irises need full sun, well drained soil and neutral pH. Give irises room as they will grow into a patch. When the patch becomes large it is likely that reblooming will be less and the patch will need dividing. After division it may take one or two years to achieve reblooming potential.
https://www.rebloomingiris.com/