thank you for contacting UNH Extension Infoline.

Ornamental grasses are usually perennials. There are some varieties that are annuals and would not return. We would need more details on the varieties to provide a more detailed answer. 

I would note that warm season perennial grasses will not start to re- appear until late April / early May.

Dutch Iris may not return due to environmental issues. The bulbs may be planted to shallowly, in which case they could have frozen over the winter. Equally they nay not have adequate drainage, which could have contributed. 

Oakleaf hydrangea should begin to leaf out in late April / early May on old wood.

Given your issue perhaps a soil test would be helpful?

https://extension.unh.edu/agriculture-gardens/pest-disease-growing-tools/soil-testing-services

I also attach a link to the Native Plant Trust, which shows ornamental grasses native to New England.

https://plantfinder.nativeplanttrust.org/cat/Ornamental-Grass

I trust this helps.