More than 900 species and cultivars of azaleas and rhododendrons exist, but only a few perform well in Iowa. According to horticulturists with Iowa State University Extension and Outreach, Iowa gardeners must select cold hardy cultivars and proper planting sites to successfully grow the flowering shrubs. Azaleas prefer partial to full sun and rhododendrons do well in partial shade in areas that receive morning sun. Both plants require well-drained, acidic soils. Once planted, they should be mulched with wood chips, pine needles or shredded oak leaves.

Azaleas that do well in Iowa are in the Northern Lights Series, which is a hybrid developed and released by the University of Minnesota. Weston hybrids are the branch of rhododendrons that grow well in Iowa.

Azaleas in the Northern Lights Series have flower bud hardiness of -30 to -40 degrees Fahrenheit and the word “lights” in their name.
– Available cultivars include: Candy Lights™, light pink flowers with pale yellow streaks, ‘Golden Lights’, gold flowers, ‘Lemon Lights’, light yellow flowers, ‘Mandarin Lights’, mandarin orange flowers, ‘Northern Hi-Lights’, creamy white flowers with yellow upper petal, ‘Orchid Lights’, orchid flowers, ‘Rosy Lights’, deep rose pink flowers, ‘Spicy Lights’, salmon orange flowers, Tri Lights™, soft pink flowers with white overtones and yellow blotch,  and ‘White Lights’, white flowers. 

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.