Which rhododendrons can be successfully grown in Iowa?

FAQ
Question: 

Which rhododendrons can be successfully grown in Iowa?

Answer: 

The most widely grown rhododendrons in Iowa are the Weston hybrids.  Introduced by the Weston Nursery in Massachusetts, these cultivars possess excellent cold hardiness.  Weston hybrids include ‘PJM’ (lavender pink flowers), ‘PJM Compact’ (compact plant, lavender pink flowers), ‘PJM Elite’ (blossoms are slightly more pink), ‘Algo’ (light pink flowers with dark pink throats), and ‘Olga Mezitt’ (bright pink flowers).  

The Marjatta hybrid rhododendrons are another group of hardy rhododendrons.  Introduced by the University of Helsinki in Finland, cultivars include ‘Elvirra’ (bright red flowers), ‘Haaga’ (rosy pink flowers), ‘Hellikki’(violet red flowers), ‘Helsinki University’ (shell pink flowers), and ‘Mikkeli’ (white flowers).