In an ideal situation, rebloomers are grown separate from the spring-only blooming irises. The two types of irises have different requirements. About six weeks following spring bloom, the non-rebloomers go dormant for the summer. In drought conditions they will even lose their fans until the cooling days of fall. Forcing once-blooming irises to continue growing can, and will, lead many to soft rot in the hot days of summer.
The care of rebloomers needs to be considered when deciding how many you need to grow. Rebloomers require faster increase, and more strength to supply the double bloom season. This often creates a faster increase of clump size. Existing advice is to grow two clumps of each iris, digging them on alternate years, so that you always have one mature clump. In tighter circumstances, you could plant just one clump and dig alternate sides each year.
Irises need a minimum of approximately 6 hours of sunshine per day. Although winters can get below zero in my zone 6 garden, summers can be brutal. Any blooms in the summer or early fall will be greatly enhanced if some shade is provided. When you don’t have space available on the east side of a building, planting tall flowers down one side of the bed can provide shade. Get creative! If this isn’t possible, know that non-shaded temperatures above 90-degrees tend to reduce any open blooms to the consistency of wet tissue; later blooms will be fine.
Spring blooming irises go dormant about six weeks after bloom season -- this is normal. If rebloomers go dormant they do not produce rebloom, so it is necessary to continue growth. Fertilize after the spring bloom season has ended. Water approximately every ten days. Supplement when Mother Nature is not on the job, but never water when the temperature reaches 90 degrees and above. It’s best to water early in the morning. Wet foliage may cause rot, so soaker hoses are a good option.
Once you determine the size and location of your new planting, it’s time to choose the reblooming irises. If you choose zone 8 or 9 rebloomers for a zone 5 or 6 garden you are sure to suffer disappointment! This is why iris research becomes very important.
If you want the opportunity of summer and early fall rebloom your best bet is to go with irises that have been reported to bloom in the summer and fall in your area. Some of the irises that have summer bloomed in my garden are 'Over and Over,' 'Immortality,' ‘Just Call Me,’ ‘Over and Over’ and ‘Echo Location.’
|'Over & Over' (Innerst 2001)|
|'Immortality' (Zurbrigg 1982)|
|'Just Call Me' (Wilkerson 2008)|
|'Echo Location' (Wilkerson 2007)|
If your goal is a fall season bloom then you might want to buy some of the fall cycle bloomers. This list includes ‘Star Gate,’ ‘Earl of Essex,’ ‘Halloween Treasure’ and ‘Harvest of Memories.’
|'Star Gate' (Wilkerson 2005)|
|'Earl of Essex' (Zurbrigg 1980)|
|'Halloween Treasure' (Wilkerson 2008)|
|'Harvest of Memories' (Zurbrigg 1985)|
In the spring you can visit gardens in your region. Many clubs maintain a display garden. This is a mission, so carry a notebook. All rebloomers do not bloom in all gardens. Even those that are reported to rebloom in your area may not be happy in your garden. It’s advisable to quiz established iris growers in your general area to determine the irises most likely to rebloom in your area.
You can conduct research on the Internet. Many of the online gardens have information about rebloomers. Remember to pay attention to the zones they are reporting. The Reblooming Iris Society has a website. A membership in the RIS includes two issues of ‘The Recorder’ each year, which contain rebloom reports from most regions. Reports of rebloom are compiled in a cumulative checklist, available though the RIS website. You can find many discussions on rebloom in the archives of both iris-talk and iris-photos. Many things iris can be located at the website of The American Iris Society.