With winter behind us, let’s think about spring and big, bold flowering shrubs.

Is the name Ericaceae familiar to you?

It’s just a fancy title for the King and Queen of shrubs: rhododendrons and azaleas.

All azaleas are members of the genus Rhododendron.

These plants are related. There is no clear-cut definition for distinguishing between the plants we commonly call rhododendrons and azaleas.

Rhododendrons are usually evergreen. Azaleas usually lose their leaves in fall. But there are exceptions to this general rule.

The flowers of the two groups tend to be different in shape and in number of stamens.

Even botanists have trouble categorizing some of these plants. This difficulty does not in any way detract from the beauty of these plants and the enjoyment that comes from growing them.

Care in planting, selection and protection of the plants is of utmost importance.

Pennsylvania has an ideal climate for rhododendrons. If you are planning to add some to your garden this spring, knowing more about their growing needs will help you select just the right spot.

There are more than 1,000 species of rhododendrons. Horticulturalists have developed improvements in foliage, flower color and quality, hardiness and growth.

Rhododendrons are native to many parts of the world, but are found primarily in China, Japan and eastern United States where soil and atmospheric conditions are ideal.

Many species of the broad-leaved evergreen shrub are popular landscape plants valued for their color, shape, low maintenance and spectacular flower display in April and May.

Flower colors vary from deep red and pink to clear white, including various shades of lavender and purple, and even orange.

Sizes vary from two- to three-feet-high to as large as 10 to 15 feet. They frequently have a spread equal to their height. It’s important to match your selection to the size of your planting site.

Before you decide which rhododendron is right for your garden, you need to understand the needs.

Most rhododendrons that you purchase at a nursery or garden center have been raised in a plastic pot. As the plant grew, the roots expanded to the wall of the pot, turned around and grew, forming a solid wall of roots.

When you remove the plant from the pot, take note that there are probably no free-growing root endings sticking out of the ball. You need to create new root endings, so that when you plant it, the free roots will grow into the surrounding soil, allowing the plant to become established and promote future growth. Failure to free these roots will most likely kill the plant within one year.

How do you solve this problem? Remove the plant from the pot and lay it on its side. Hold the plant by the trunk directly above the crown. With a sharp knife, starting at the top of the ball, make four cuts, 90 degrees apart, one-inch deep, all the way to the bottom of the ball. You have now freed the roots. Reach into the slits with your fingers and gently pull out several roots.

Rhododendrons require acidic soil for proper growth and nutrient uptake. Try to adjust the soil pH to as close to 5.5 as possible. The pH is the standard measurement of soil acidity with a scale that runs from 0 (acidic) to 14 (alkaline). A pH of 7.0 is neutral, neither acid or alkaline. Soil can be acidified with applications of sulfur, aluminum sulfate or ferrous sulfate.

Rhododendrons also respond to applications of iron chelate if the soil pH is on the high side. The best way to know your soil pH and to know what you need to add for optimum growth and good leaf color is to take a soil test.

You can purchase a Penn State soil test mailing envelope from your local Extension Office. You send your soil to Penn State for an analysis.

For the best growth and development, you will need a site that is protected from strong winter sun and wind, where humidity is high and where soil is well-drained, acidic, and has higher than normal amounts of organic matter.

Azaleas are an ideal choice as a companion for a planting of rhododendrons. Again, you have a wide selection. The old reliable evergreen azalea should be used with caution, because hardiness in the Lehigh Valley can be a problem.

We are familiar with the mass of blooms on the plants that Mom gets for Easter and Mother’s Day. Some, but not all of these plants, are hothouse varieties and cannot be added to your landscape.

A better investment would be to ask your nurseryman to help you select a hardy azalea that will bring beauty to your home for many years.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613.