Yes, the + after an OGB means that the iris has a
high amount of aril blood. Even here in my climate, in a raised bed,
some of the OGB+ varieties are not reliably hardy. It depends on whether
the greater amount of aril blood is oncocyclus or regelia (regelia is
hardier). The - designates that there is but a quarter aril blood in the
mix. Of the two iris you pictured (nice photos!), Omar's Gold and Persian
Sapphire, both of these have SDBs in their backgrounds, and that makes them
hardier, in my estimation. The fact that you grow them in a raised bed has
a lot to do with your success.
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