It’s been years since I had a rose of Sharon. I don’t remember how long it bloomed but it did get very big. At least 10’
I live in SE Wisconsin and I've seen some that have been pruned into what look like small flowering ornamental trees! That's how big they can get. I cut mine back after blooming season every year a good 2-3 feet -- they can grow that much in a single season. As for length of blooming, mine start late, usually not until September, but then they will bloom for a good six to eight weeks, depending on the weather conditions. If they get good water and lots of sunshine, the blooming period lasts longer. They are the final things to bloom in my garden, outlasting even my late-blooming hostas that start in the 3rd or 4th weeks of August.
Thanks for the information, I thought they bloom in spring, wow they grow that much in one season. I also live in Wisconsin.
I live in Milwaukee County in the SW corner of the City of Milwaukee close to Greenfield. If you live further north I imagine the shrubs will adapt and bloom earlier because - as you know - the further north you go the earlier the first frost and snow comes, sometimes in October. Spring was late here this year so my 3 shrubs will be blooming later. They appear to be fully leafed out now, but haven't started forming flower buds yet. That will happen now over the next several weeks. If it stays warm as it has been here and we get enough rain instead of the mini-drought for July and August like last year, they would probably bloom earlier. I've already watered my back yard once, that is where the shrubs are located. They are planted in a raised bed that is about a foot off the ground, backed by a 6 foot tall privacy fence. Typically the shrubs will shoot up at least a couple feet taller than the fence by the end of the growing season, and I will cut them down an addition foot below the top of the fence so, about 3 feet is removed. They're tough and hardy, they can take it.