By Brenda Bye, Master Gardener Volunteer
One of the reasons that I love spring in the Willamette Valley is the masses of colorful rhododendrons. It’s hardly surprising that this flowering shrub is so popular, because it comes in a wide range of sizes and colors. Many species are evergreen which is an additional bonus to add structure to your garden in grey winter months. Spring is a great time to plant rhododendrons and it’s not too late.
There are about thirty species of rhododendron native to North America. They are found naturally in temperate deciduous forests and enjoy the acidic soil found in these wooded hills and mountains. If you are looking to plant a Northwest native, consider Rhododendron Macrophyllum, the Pacific Rhododendron. Its flowers can range from pale pinks to deep purples. It will grow to be 8 to 10 feet in the garden but can grow much bigger in the wild.
Another interesting native is Rhododendron Occidentale, the Western Azalea. Its flowers range in color from white to pink, but all have a yellow spot on the upper petals that adds interest and beauty. Their flowers are known to be quite fragrant. Unlike the Pacific Rhododendron, the Western Azalea is deciduous and can have very pretty autumn foliage.
Regardless of which rhododendron you choose, they require similar growing conditions:
- Acidic soil with a pH usually between 4.5 and 6
- Soil that drains well and is rich in organic matter
- A consistent level of moisture
- Dappled shade, although it will tolerate a variety of sun exposures
Having the right soil conditions is very important before you plant your rhododendron. Many of us in Western Oregon already have acidic soils but if you have questions about getting your soil tested or how to interpret a soil test, I would recommend reaching out to your local OSU Extension Office. You can also reach them online at https://extension.oregonstate.edu/ask-expert.
Rhododendrons can be prone to root rot. That is one reason to mix in a good amount of organic matter into your planting site. Some sources recommend a mix of 50% organic matter. In addition to building healthy soil this organic matter will make sure the roots are getting oxygen and not becoming soggy. Organic matter also helps to feed your plant to keep it healthy.
Before you place your new rhododendron in the ground make sure to water it well. When you place the root ball in the ground it should be planted at the same level as it was in the pot. Then mulch it with a thick layer of pine bark mulch, which is good for those acid loving plants. Make sure there is a nice ring of space between your trunk and your mulch to prevent fungal diseases. As the mulch breaks down it will also provide more nutrients to your rhododendron.
Although rhododendrons have specific soil requirements, they are very easy to care for once planted. The mulch and organic soil you used will help the soil have consistent moisture, but they may need additional watering in the heat of summer. They generally don’t need to be trimmed but do benefit from deadheading spent flowers. Rhododendrons appreciate a yearly fertilizer in the fall and a refresh of their mulch.
Rhododendrons look great as foundation plantings around your home. Their range of colors will fit into any planting scheme and they will bloom for years to come. If you don’t have one yet, consider planting a rhododendron.
If you are looking for more information about this flowering shrub, check out the resources of the American Rhododendron Society, www.rhododendron.org. And here is a very in depth article from the Pacific Horticultural Society about the Western Azalea https://www.pacifichorticulture.org/articles/western-azalea-beauty-and-fragrance/.