Planting, Growing, Caring & Pruning Rhododendrons

While driving through the Appalachian Mountains during the spring and early summer you'll notice flashes of color on the hillsides. Those are the huge native rhododendrons blooming with abandon. They thrive in in the cool summer conditions and dappled shade provided by the pine and oak forests in the mountains. Lucky for home gardeners, the wild shrubs have been selected and tamed into well-behaved garden specimens suited for even the smallest courtyard spaces. While their flowers are the flashiest attributes, the evergreen leaves of most rhododendron varieties make a great garden backdrop year-round.

Here's how to grow rhododendrons.

How to Choose Rhododendrons

The two main things to consider when selecting rhododendrons are your hardiness zone and the amount of space available for the plant to grow. There's a broad range of mature plant sizes and temperature tolerances among rhododendron varieties.

For example, P.J.M. hybrids are among the most reliably cold-hardy rhododendrons. Korean rhododendrons (Rhododendron mucronulatum) are also a good cold-hardy choice, though they lose their leaves in the cold months. 'Scarlet Wonder' is a red-flowered dwarf variety with a maximum height and spread of just 2 to 3 feet, perfect for small spaces.

Where to Plant Rhododendrons

Traditional rhododendrons thrive in filtered sunlight and acidic soil. Newer varieties can tolerate a range of sunlight conditions, but always check the plant tag or description when shopping to make sure the plant needs match your garden conditions. The warmer your region, the less hot afternoon sun the plants will tolerate. All rhododendrons grow best in soils with a pH between 4.5 and 6.0. Use a soil testing kit to check; if the pH tests higher than 6.0, apply aluminum sulfate to the soil according to package instructions.

How to Plant Rhododendrons

Read the plant tags and determine the optimum spacing for the rhododendrons you've purchased. Rhododendrons do not need (or like) frequent pruning, so the initial spacing is important for long-term plant health. Follow these steps:

  1. Dig a planting hole that is twice as wide and just as deep as the root ball of your rhododendron plant.
  2. Remove the plant from its container and place it in the planting hole. The top of the root ball should be even with the soil line.
  3. Mix the soil you removed from the planting hole with Miracle-Gro® Garden Soil in a 50:50 ratio, then fill in around the plant. Adding Miracle-Gro® provides a boost of nutrition and will help your plant grow strong roots.
  4. Water thoroughly.
  5. Add a 2- to 3-inch layer of mulch around the base of the plant to help keep soil moist. Be sure you don't mound the mulch against the plant.

How to Water Rhododendrons

Rhododendrons are shallow-rooted plants that require water twice per week during the first growing season. Once plants are established, though, you should only have to water during dry periods (2 to 3 weeks without rain). Though rhododendrons need consistent moisture, they do not do well when sitting in wet soils, so always allow the soil to dry between waterings.

How to Feed Rhododendrons

A month after planting, begin feeding rhododendrons with Miracle-Gro® Water Soluble Evergreen & Acid Loving Plant Food, which is specially formulated for acid-loving plants. For easy application, consider the Miracle-Gro® Garden Feeder, which lets you feed and water at the same time. As with all products, be sure to follow label directions.

How to Prune Rhododendrons

Unlike their close cousins, the azaleas, rhododendrons neither need nor respond well to frequent hard pruning. That's why initial selection and spacing of the plants are so important. Still, you can prune to remove dead or diseased wood at any time, and it's fine to prune lightly to control size after flowering. You can also deadhead rhododendrons after flowering by snapping off the flower clusters where they meet the stems. This will encourage the plants to direct energy into growing roots and developing next year's flowers instead of developing seeds.

How to Grow Rhododendrons: Recap

Ready to start growing rhododendrons? Click on any of the product links above for more information, to purchase the product online, or to find a retailer near you.