The Homeowners Column

The Homeowners Column

University of Minnesota Develops Hardy Azaleas

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

A family vacation through the Southern states in the spring will surely yield pictures of relatives standing next to the blooming azaleas. The magnificent colors and profuse blooms of azaleas capture our hearts and imaginations. We imagine that same look in our own gardens.

Unfortunately, azaleas can be difficult to grow in Illinois. One definite challenge is their lack of cold hardiness. In 1957, the University of Minnesota started its azalea breeding program. Twenty-one years later the first in a series of cold hardy azaleas was introduced to the nursery industry. They are a group of beautiful shrubs that are cold hardy to zone 3 and flower bud hardy to minus 45°F.

Plants coming out of the Minnesota program are called the 'Northern Lights' series. Under good growing conditions, 'Northern Lights' will reach a height and spread of eight to ten feet, a perfect background in any garden.

'Northern Lights' are available in a wide variety of shades of orange, pink, white or yellow. Their names include 'Lemon Lights,' 'Northern Highlights,' 'Pink Lights,' 'Rosy Lights' and 'Orchid Lights'. An added benefit is their magnificent fragrance. They bloom from mid-May to the first of June.

If all that wasn't enough to convince you of the beauty of 'Northern Lights' azaleas, they add a tremendous show of fall color. A flush of maroon to red will engulf the plant as your garden goes to sleep for the winter.

Although we often think of them as different plant groups, azaleas and rhododendrons belong to the same genus – Rhododendron. Traditionally azaleas are deciduous and rhododendrons are evergreen.

Cold hardiness is only one of the challenges to growing azaleas and rhododendrons. Since azaleas grow naturally in wooded areas in well-drained acidic soils high in organic matter, we must mimic these conditions for the plants to grow well.

Before planting, get a soil test to determine its acidity and how much sulfur is needed to lower the pH to 4.0 to 5.5. Add organic matter such as leaf compost or peat moss to the top twelve inches of soil. In areas of poor drainage, 12-inch tall raised beds may better insure the plant's survival.

Azaleas are shallow-rooted, so mulching with wood chips, a regular supply of water and no hoeing are crucial. Root rot can result if the azaleas stand in water for even a short time.

Azaleas can also be reluctant to grow out into the surrounding soil once they are planted. Pot-grown azaleas are especially prone to this. If possible, find field-grown azaleas.

To help pot-grown azaleas grow into the surrounding soil, be sure to score the root ball by running a sharp knife down the root ball in several places to encourage new root growth.

All azaleas are heavy feeders and enjoy a regular dose of fertilizer. Water-soluble, acidic fertilizers are usually the best to use.

Azaleas produce their flower buds in the late summer or early fall of the previous year so pruning should only be done right after blooming. Azaleas will grow in sun or partial shade. More flowers are produced in sun, but shade-grown azaleas require less water and offer more brilliant colors.

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