Rhododendrons are shrubs, often evergreen, that are either native to North America or hybrids grown for desirable attributes such as height, color, and adaptability to regional climates. Their flowers are tubular-, funnel-, or bell-shaped—and depending on variety, can be fragrant.
With more than 900 known species in the genus and available in a range of sizes, habits, and flower color, rhododendrons are one of the most useful shrubs in the home landscape. Though we often speak of them as different groups of plants, rhododendrons and azaleas actually both belong to the genus Rhododendron.
While both stars in the landscape, Rhododendrons typically have much bigger flowers than azaleas, bloom later, and are open and not as dense in their habit (all good reasons to mix and mingle them in the landscape).
With so many gorgeous varieties in a range of mature plant sizes and temperature tolerances from which to choose, picking the right rhododendron for your garden can be a challenge. Here are the questions to ask and answer:
- What's my zone?
- How much planting space do I have?
- When do I most need color in the garden?
- What color speaks to me?
The first two things to consider are your hardiness zone and the ultimate amount of space available for the plant to grow. Most are hardy in zones 5 – 8, though there are a some varieties that can take more chill (some are hardy to zone 4) and others that can take a bit more heat (some are hardy to zone 9).
Rhododendrons range in size from compact (perfect for containers, along a woodsy walkway or in front of taller shade lovers) to hedge height (ideal under tall conifers, along property lines or to add a focal point). It's important to be realistic about how much space you have to fill because choosing the right variety now will make life easier later.
Once you have figured out these two considerations, your third decision is if would like one that blooms earlier or later in the season, and finally (the most fun) choosing from a wide variety of colors which can range from white, red, pink, purple, orange or yellow, depending on the specific variety.
Now that you have selected the perfect plant for your particular landscape there are just a few things to know about planting and care. Rhododendrons are not especially fussy, but they do have needs. Finally, as these shrubs bloom over a relatively short season, it's good to add a few companions with similar light and soil requirements to keep the show going longer into late spring and early summer. More on all of this below...read on!
North American native rhododendrons typically thrive in filtered sunlight and acidic soil, but modern varieties can tolerate a wider range of condition. If you are unsure about the light and soil condition in your garden garden ask for advice at your local garden center and always check the plant tag to make sure your site can provide what the plant needs. The warmer your region, the less hot afternoon sun the plants will tolerate and in colder zones (4) planting where there is protection of cold winter winds is helpful. 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.
When you consider that native rhododendrons thrive in the dappled woodland shade and under trees with which they have grown (planting a young rhododendron under a mature tree is tricky and they often fail), it is easy to understand their preference for moist, well-drained soils high in organic matter. Rhododendrons and azaleas have shallow fine hair-like roots and do not tolerate water-saturated soil conditions--but do require moist soils. Monrovia's rhododendrons are container-grown in a custom soil blend with added mycorrhizae so once planted in the correct soil, they will naturally get off to a great start. If your soil lacks excellent drainage, amend prior to planting with a mix made for acid-loving plants.
Once established in a location that suits their particular needs, rhododendrons are typically fuss free, needing only the basics--food, water, and pruning--to thrive.
- Watering: Because of those shallow roots plants need consistent water during the first growing season. If there is no rain, water deeply twice a week and in subsequent years, once plants are established, only dry periods (2 to 3 weeks without rain). Remember, many a rhodie has been felled by sitting in wet soils, so always allow the soil to dry between waterings.
- Feeding: If your garden's soil isn’t wonderfully rich or fertile, your rhododendrons will appreciate a balanced fertilizer if your soil is naturally acidic or a specialty acidic fertilizer if not. Either way, the time to feed is when plant and again in early spring as flower buds swell.
- Pruning: Here's the good news--rhododendrons neither need nor respond well to frequent hard pruning, so you can holster the clippers. However, pruning to remove dead or diseased wood at any time or pruning lightly to control size after flowering will not harm your plant. After flowering deadhead by snapping off spent flower clusters to encourage root growth.