Azaleas & Rhododendrons

- St. Louis

The most vivid spring color display in St. Louis is the annual celebration by azaleas and rhododendrons.The breathtaking colors of lavender, red, white, violet, pink, scarlet, and even yellow and orange is unmatched in the landscape. This article will address the evergreen varieties mainly.  The cultural practices for azaleas and rhododendrons are very similar.   

Growing Azaleas and Rhododendrons

One of the most important keys to growing azaleas and rhododendrons is selecting the proper location.  Protecting the plant from the winter elements is important to the survival of these plants.  The north and west side of the residence will greatly enhance the winter hardiness of the plant especially in partially shaded areas.  It is best to maintain constant temperatures during the winter; the freeze/thaw cycle subjects the plant to severe winter stress. 

Purchasing plants from climates similar to St. Louis will aid in the plants survival.  Greenscape Gardens purchases most azaleas and rhododendrons grown in Pennsylvania and Northern Illinois.  These northern grown varieties have a better chance of survival when properly planted and sited.  Discount and hardware stores are purchasing southern grown plants which can not survive our winters.

Another important factor to consider when planting azaleas and rhododendrons is to properly prepare the planting site.  Select a planting site away from shallow rooted trees such as maples and ash.  Grouping of three or more plants are much more attractive than single plants.  Arrangements of the same flower color are also more breathtaking than a checker board of colors. 

Our heavy clay soil must be properly amended.  The following plant preparation should be followed for maximum results.  Remove 6 inches of soil in the bed area, replace with composted topsoil.  In areas where drainage is poor, create a raised bed or berm in the area to a height of twelve inches using composted topsoil.  Develop a berm which has natural landscape appeal.  Do not make a gravesite hill but a visually appealing, sweeping kidney shaped mound. 


Dig a hole for the plant approximately 50% wider than the root ball.  The depth of the hole should be less than the height of the root ball.  We prefer to plant the azalea and rhododendron two inches higher than in the previous plant medium.  Settling will occur and mulch should be placed around the plant.  Planting too shallow is better than too deep.  Another important care factor is to tickle the roots.  Plants grown in containers will have a mass of feeder roots along the plastic wall.  After you remove the root ball from the container, cut the root ball ¼ inch deep at approximately 1” intervals.  This allows the root system to expand from the previous enclosure and radiate into the surrounding soil.  If the bottom is root bound do the same procedure.  Backfill the root ball with a 50% combination of existing soil and compost.  Thoroughly soak the planting zone.  A liquid root stimulator will greatly enhance the plant’s growing conditions 


Apply a two inch layer of hardwood bark mulch around the base of the plant.  Azaleas and rhododendrons are shallow rooted and need a heavy mulch to conserve moisture around the roots and reduce potential winter damage.  Do not disturb the root system by cultivating the soil, this will destroy the small feeder roots.  Planting annual flowers in azaleas is not recommended because of the damage incurred during planting.  Keep the mulch around the plants all the time.  This will improve the overall quality of the plant plus it will reduce potential lawn mower damage. 


NO FERTILIZER SHOULD BE APPLIED TO THE NEWLY PLANTED AZALEA OR RHODODENDRON THE FIRST YEAR.  Sufficient nutrition will be available from the compost which was used in the planting process.  Non-organic fertilizer will burn the tender feeder roots. 


Azaleas and rhododendrons require a minimum amount of care once properly established.  Do not cultivate around the root zone of the plant.  Serious feeder root damage will occur.  Maintain a two inch layer of mulch around the base of the plant at all times. 


Use Fertilome Azalea and Rhododendron Feed.  This specially formulated fertilizer is for acid loving plants.  Follow label recommendations.  The initial fertilization should be in early May (when the plant has finished blooming).  The second treatment should be applied on June 1st and the final application on July 1st.  Add sufficient water around the base of the plant after fertilizing.  This three step fertilization program will create a healthier plant with many more blooms the following year.


Avoid excessive watering.  More azaleas and rhododendrons have been killed by over watering.  The soil should be thoroughly moist before cold weather sets in.  Remember around Thanksgiving to give these plants a thorough soaking. 


Proper pruning is the secret to a great spring display.  After the plants have completed their flowering cycles, remove the flower stems on rhododendrons.  This is not as important on azaleas but it will make the plant much more presentable. Azaleas and rhododendrons should only be pruned after they are finished blooming.  When properly pruned an azalea will regenerate four to seven new shoots and rhododendrons will normally produce three or four new shoots.  Selectively prune the plants to improve the form by removing the soft, new shoots of vigorous growing stems.  This will make the plant more compact and it will also increase the amount of stems and potential flowers for the upcoming year. 

Winter protection

Winterization of the plant is necessary to insure the vitality of the plant.  Winter sun and cold wind are the two main problems for winter survival.  Planting location is key in reducing both of these situations.  Placement on the east side of the house is the optimum location since it will have the most winter protection.  Applying Wilt-Pruf will significantly reduce winter desiccation.  Insulating the base of the plant with a two or three inch layer of hardwood mulch will also reduce winter damage. 


  1. Properly prepare the plant site

  2. Choose only winter hardy plants

  3. Score the root zone of the plants (tickle the roots)

  4. Thoroughly water after planting to reduce air pockets

  5. Do not fertilize for the first year

  6. Properly fertilize after the first year with specific feed, three times.

  7. Selectively prune for natural compactness and maximum flower production

  8. Winterize the plant


Greenscape Gardens Recommended Azaleas & Rhododendrons

Azaleas Evergreen Varieties

Ashley Marie

Extremely unusual azalea.  Foliage is variegated green with white fringe on the edge.  Needs good winter protection.


Flowers are a watermelon pink.  A very striking color in the landscape.

Delaware Valley White

Flowers are pearl white. 

Girard Hershey Red

Flowers are a very deep red color.  Interesting winter color.

Girard Hot Shot

Large flowers in a deep orange-red to scarlet.  Plants develop an orange-red color in the fall for winter color.

Girard Renee Michelle

Flowers are a clear pink and are large and showy.  A very cold hardy variety.

Girard Rose

Large wavy rose colored flowers.  The leaves turn reddish in the winter.  A very cold hardy variety.

Girard Pleasant White

Flowers are white with a cream center.  The flower is very prolific, great bloomer.  Plants are hardy and one of the last to bloom.


Flowers are vivid red.  Very hardy variety.


Lavender flowers.  Plant is very open and extremely cold hardy.



Album Elegans

The flower is a soft lilac color fading to white.

Catawbiense Album

White flowers in round trusses.  Narrow leaves, tall and vigorous

Nova Zembla

These flowers are a deep red color.  Plant is cold and heat tolerant.

Purple Splendor

A very deep violet purple with a dark blotch.  Very hardy.


Lavender pink flowers.  The leaves are small and turn purple in fall.

Roseum Elegans

The flowers are a lavender pink color.  Plant is very hardy.