Q. I love azaleas and rhododendrons but I have a hard time getting them to grow at my home. What can I do? Signed John K.
A. Flowering rhododendrons and azaleas steal the show each spring. Their beautiful blooms are so spectacular it is no wonder that they are so popular. Rhododendrons are not native to Michigan, but are very adaptable to our landscape. Azaleas and rhododendrons will do well with the right soil conditions and the proper planting location. We can amend the soil to create the proper soil conditions, but for best results we need to carefully choose the best planting location.
Proper planting is essential for azaleas and rhododendrons. The exposure of the plants to winter winds and sun needs to be limited. Generally azaleas and rhododendrons do best on the north side of a building, solid fence or wall. Another spot may be between established evergreens for protection from high winds and the winter sun. Some of the smaller leaf varieties of rhododendrons and azaleas will tolerate more exposed locations.
These plants like moist soil conditions but not soggy soil. A well-drained location that will receive rainfall or irrigation is best. To test your soil for drainage simply poor a bucket of water in your hole, if it does not drain in a few minutes you have poor drainage. The soil drainage can be improved by raising the level of the soil. Do this by tilling into the top 6” of the soil a mixture of compost and topsoil. Raise the soil level up to the point that your soil will drain when you do the water test. This is usually 3-4” of soil at a minimum. Adding organic material such as sphagnum peat moss, compost or pine bark will help keep the soil loose and even lower the pH of the soil.
The pH of the soil for azaleas and rhododendrons should be between 5.0 and 6.0. You can test your soil if you are unsure of the pH level with some simple one-time testers. With these testers you simply add a small amount of soil to the test container provided and then fill with water and shake. After the soil has settled you compare the color of the water to the chart provided to determine the pH. There are some more elaborate testing methods available also, but for 99 cents it gets the job done. To lower the pH you add iron sulfate (Ironite works great) or aluminum sulfate. Lime will raise the pH if you soil is too acidic. In most cases you will be lowering the pH. Mix the Ironite or aluminum sulfate as directed on the package into the soil before planting and around existing plants.
Azaleas and rhododendrons do not require as much maintenance as most people think. If you prepare the soil as we described above the soil will hold enough moisture between watering and still drain off the excess. A layer of mulch will hold the moisture in the soil so watering will only be once or twice a week depending on how dry the weather has been. Avoid daily watering for it may lead to root rot diseases. The easiest way to test the soil to see if your plants are receiving enough water is to gather a small amount of soil from just below the surface. Squeeze a handful of soil. If the soil is crumbly when released you need to water more. If the soil is wet enough that your hand gets wet then you need to cut down on the watering.
Fertilize your plants with granular fertilizer made just for azaleas or rhododendrons in late spring and again in late summer. A soil acidifier such as Ironite is also recommended in your fertilizing program. Liquid fertilizers such as Miracid are fine, only they need to be applied more often since they are not slow release. Organic fertilizers like Espoma Azalea and Rhododendron Food will last for months giving your plants a steady supply of nutrients.
Pruning the azaleas and rhododendrons should be done after they bloom. Pinching off the spent flower will transfers the plant’s energy to growth instead of seed production. By removing the terminal bud on the taller branches you can push the growth on the lower branches, producing a more dense plant.
A healthy plant is your strongest defense against insects and diseases. Black vine weevils are the insects that have been known to attack rhododendrons. A saw-toothed chewing on the leaf margins indicates the presence of adult weevils. The larva from these weevils does the most damage to the plant by eating at the plants roots. Control can be achieved by using nematodes (a beneficial microscopic worm) or Merit, produced by the Bayer company, a systemic insecticide which travels throughout the plant killing the insects when they eat the plant.
Proper installation of azaleas and rhododendrons is the key to success for you. By following the guidelines above your plants should thrive. Try planting exbury hybrid azaleas or P.J.M. rhododendrons if you do not have a protected northern exposure. These varieties are hardier and can withstand more exposure to the wind and sun. Now lets enjoy the show of our azaleas and rhododendrons.