Arpil 3, 2002
Woodbury Bulletin
Betsy Halden

Growing azaleas and rhododendrons in Minnesota

Several seasons ago I planted a lovely Orchid Lights Azalea in our front yard. It has bloomed every year with lovely fragrant flowers. This year I would like to add rhododendrons and azaleas to our plantings. Azaleas and rhododendrons are spectacular flowering shrubs. The keys to successfully growing these plants in our area are selection of cold hardy varieties, correct placement in the landscape, and proper planting. If you would like to grow these attractive shrubs, here are some suggestions and some information.

Botanically, all azaleas are actually rhododendrons. They belong to the genus Rhododendron, one of the largest genera of woody plants, containing over 800 species. However, the deciduous types are commonly called “azaleas,” while the evergreen species and varieties are referred to as “rhododendrons.”

Two of the most popular varieties of azaleas and rhododendrons for our area are the Northern Lights series of hybrid azaleas and the P.J.M. rhododendron. The Northern Lights series of azaleas is a group of hybrid azaleas developed and released by the University of Minnesota. All the varieties in this series have flower bud hardiness of –30 to –45 F and the word “lights” in their name. ‘Northern Lights’ was the initial introduction. Flowers range from light to dark pink. Two varieties which were selected from ‘Northern Lights’ are ‘Pink lights’ and ‘Rosy Lights.’ Flower colors are lights pink and deep rose pink, respectively. other varieties in this series are ‘White lights,’ ‘Orchid Lights,’ ‘Spicy Lights,’ and ‘Golden lights’ with white, orchid, soft orange, and gold flowers. Two of the newest members of this series are ‘Northern Hi-lights,’ ‘Mandarin Lights’ and ‘Lemon Lights.’ ‘Northern Hi-lights’ has creamy white flowers. Each flower is accented with a bright yellow upper petal. ‘Mandarin Lights’ and ‘Lemon Lights’ have mandarin orange and light yellow flowers, respectively.

The ‘P.J.M. rhododendron was named for P.J. Mezitt, the hybridizer of the cultivar. The P.J.M. rhododendron grows well over much of the upper midwest. The small, evergreen foliage is dark green in summer, but turns to a maroon-purple in the fall. The flower buds are hardy to – 35 F. The plant produces bright lavender pink blossoms in mid to late April. The mature height and spread of the P.J.M. is approximately 4 to 6 feet tall.

When planting rhododendrons and azaleas, it is important to choose a proper site. Azaleas prefer partial to full sun. Rhododendrons perform best in protected sites in partial shade. An area that receives morning sun and afternoon shade would be a good site for rhododendrons. Avoid windy, exposed sites. During the winter months, the cold, dry winds and sun can dry out the rhododendron foliage and cause extensive leaf burn.

Avoid planting rhododendrons and azaleas too deep. Most of their roots are within the upper four to six inches of soil and should not be buried deeper than they were previously growing. Dig a shallow hole and backfill around the plant with a mixture of acid peat and existing soil.

Rhododendrons and azaleas require well-drained soils with pH of 4.0 to 5.5. The pH of most garden soil ranges from 6.0 to 8.0. If your soil is not acidic, you can add peat, sulfur, or ferrous sulfate to lower the pH. Adding organic matter such as compost, manure, sawdust or acid peat moss will help. In order to determine the pH of your soil you can request a soil test by sending a soil sample to the University of Minnesota soil testing lab. For a nominal fee they will give you a computer generated soil report with recommendations for fertilizer or amendments for the types of plants you would like to grow.

Placing rhododendrons and azaleas in a wet, poorly drained soil is a death sentence. They will invariably die. Gardeners with poorly drained sites should build berms or raised beds to insure good drainage.

The University of Minnesota Extensions Service has an informative fact sheet on “Growing Azaleas and Rhododendrons for Minnesota.” You can find it at the University of Minnesota Extension Service web site www.extension.umn.edu. Click on gardening or enter ‘Growing azaleas and rhododendrons” in the search box.

Betsy Halden is a resident of Woodbury. She consulted Cornell Cooperative Extension and the University of Minnesota Extension Service materials when preparing this column. You can reach Betsy Halden at eahalden@comcast.net