I grow a lot of "re's", and I'll tell you my "secrets"....but don't spread them around
! First off, mine grow in zone 5a...so I'm WAY colder than you, but, that just means getting rebloom should be easier for you !
I'll start with a few "generalities". You will find that some re's need to be divided quite often, to get rebloom, while others really "resent" getting disturbed.....you will figure out which is which, as you go along. Also, you need plants that are "zoned" correctly (or , at least "close to correctly") for your zone....and that really won't matter too much, to you, as you are 'zoned pretty high", so almost ALL the re's should preform , for you.
I fertilize , in spring, as soon as new growth begins (all my irises)...use a "balanced" fertilizer. "Common knowledge" says don't use anything high in nitrogen (that's the first "number" in the ratio: 10-10-10, for example) I believe in soil tests!! Your extension office can fix you up with a commercial "tester", and the info you'll need to collect, and submit, the soil samples, or, there are "home" test kits, available. No sense putting something on that you don't need ! I've found that , in order to get rebloom, they need "extra", or "more" fertilizer, than the "spring only "irises, so , just before spring bloom...when you se the first stalks starting, I give the re's another "small" dose of fertilizer, and ANOTHER dose, when spring bloom is done...and by "small", I mean , maybe, 2 tablespoon per clump, scratched into the soil ,around the base of the plant. If re's are going to rebloom, they can NOT be allowed to "go dormant" ! All irises WILL go dormant, when spring bloom is over...they are "resting" before they start making increase...so, how do you keep them from going dormant ? Water, and food. When the soil gets dry, to a depth of about 1"-2"...water them well....no mulch around the plants, though, because with the extra water, and richer soil, soft rot will be a problem if the soil is mulched. If you keep them actively growing through the summer dormant period (for most irises, that's about a 4 week period, following spring bloom). I know I'll hear lots of ", Not too much water...not too much fertilizer", but, all I can say, is it works for me.
I grow most of my re's in "dedicated" re beds...that makes it much easier to give THEM the extra rations, without "overdoing it" on the spring only irises. If yours are "mixed" with "spring only" irises, just be "careful " with both the water , and the food. If I was smart enough with the computer , I'd make a graph showing "when" I feed, but, 1st dose (all iris), just as new growth starts in the spring. 2nd dose (re's) just as stalks are starting in the spring. 3rd dose (all irises) when spring bloom has ended, and you have removed all the spent stalks. Subsequent doses for the re's, about every 2-3 weeks, until the season ends (for me , that a "freeze"....for you...maybe you can get bloom all year ?!?)
Try this on a few "test plants", and see what results you get ! As I said, the extra water, and "food" sort of "goes against" all the "iris lore"....but it works for me !
