imo... grasses never need water ... after the first year...

new plants this year ... need to be protected against drought ...

first things first.. let you lawn go dormant ...pshaw on lawn .. lol ...

but the base question is.. how do you water ... do you insert finger.. and find out when the soil is dry ...

or do you just go out there every day for your meditation .. and just water everything???

what is your base soil.;. is there mulch ... how do you water ... i hope you are using a water wand.. rather than sprinklers.. to put the water on the ground.. not in the air ...

the hardest thing you could learn.. would be to let fully established plants wilt.. before you water again ... take notes.. and learn how long that is.. in your micro climate ... in your soil.. with your plants .... you would probably be amazed.. how little water is really needed .. and how much you have been babying your plants ... and plants arent children ... show them who is in charge ...

ken

https://duckduckgo.com/?q=water+wand&t=ffcm&iax=1&ia=images

Everything Ken says... plus I might add I never water my hostas; sedum are succulents, no need to water. Don't drown those arborvitae; check moisture level first. Hydrangeas would be the first to need water; at least for me.

Ken's questions: "what is your base soil.;. is there mulch ... how do you water?" are important. If they aren't mulched, plan to do that to help preserve moisture as well as suppress weeds. Natural precipitation amounts are important as well, so get a rain gauge and set it up far enough away from buildings and trees so it is reasonably accurate. Consider adding a rain barrel or two as well. You can get a diverter to put in the downspout so the water only does to the barrel when there is room, and you can empty the barrel for the winter.

Of the plants you listed, I have Ninebark, Techny arborvitae, and Hydrangea paniculata (different cultivars than Little Lime, but I don't think different as far as watering needs) in a bed that hasn't been watered since its third year. The bed is in full sun and has good organic content in fine sandy loam soil and is mulched with shredded wood, and despite having an official drought here last year that was only broken this May, I didn't water and I didn't see any issues with any of these plants. I would continue watering new plantings such as the Techny arborvitae, boxwood, etc as needed. Stick your finger down into the soil at the base of the plant and see if the soil is moist to know if watering is needed. Long slow soaks are best, and I have used soaker hoses under mulch to make sure that the water goes to the soil, not evaporation. Annabelle in sun will need plenty of water, so you might consider moving it to a morning sun spot and planting something more drought tolerant in the sunny spot. I almost never water my Annabelle in afternoon shade.

Generally grasses and Sedum are pretty drought resistant.

Water the newly-planted when they need it (finger-sticking for gauge) and watch the older plants for drooping. And mulch everything.

The biggest problem you are going to have is getting the plants adjusted from overwatering. If this has been going on since they were planted, they probably have very shallow, poorly developed root systems since they have never had to forage for water. So they are going to be a lot less drought resistant than plants that have been watered appropriately. Long term, the only one I'd expect to need anything like regular watering is the Annabelle hydrangea.

Not enough info to answer. In a perfect world, these are planted individually and competition does not play a role. In practice, people make beds and there are often trees.

Beyond that, if you are in your third year, it's time to think about letting them go rogue...feral...whatever. a lot of that depends on the year, though, and what else is going on (competition).

The easy answer is, let the grass go. Each of us have different priorities, however, and we each get to make our own choices.