Are Rhododendrons Annual, Biennial, or Perennial Plants?
So you've decided you want to add some rhododendrons to your garden this season, but want to know if you'll have to replant them each year before you do? In this article, we take a look at the rhododendron life cycle, and if they are considered annual, biennial, or perennial plants!
Perennials are often the standout features in landscaping. These plants make things easier on gardeners and homeowners because they’ll keep coming back year after year. You plant them once, then, with proper care, get gorgeous blooms year after year.
Rhododendrons are one of the most beautiful ornamental shrubs. They start out as smaller flowering bushes and can grow into a central feature after a few years. In some cases, you could even use them to build a floral privacy screen. But will they come back each year, or will you be stuck replanting them each season?
The first step in properly caring for these blooming beauties is understanding their life cycle and what type of plant classification they have. Keep on reading to find out everything you need to know about the Rhododendron life cycle, and if they are considered annual, biennial, or perennial plants!
The Short Answer
Rhododendrons are ornamental perennials that thrive in USDA Hardiness zones 4 through 8. However, that doesn’t mean you can’t grow them in your zone 3 or 9 gardens. In fact, rhododendrons are one of the hardiest perennials you could put in your garden.
The Long Answer
Annuals are plants that need to be planted again each year. They die back at the end of the season and will need to be removed and then replaced. Annuals tend to be showier, brighter in color, and larger than perennials.
Plants that do not die each season and can typically survive winter cold are called perennials. You should not have to ever replant perennial plants. They can last from two or three years up to 30 or more! Of course, this all depends on their growing environment and care.
Rhododendrons are classified as perennial evergreen shrubs. Evergreen means they will not lose their green foliage. It will remain even through their dormancy period in the winter.
A shrub is a woody plant that is not big enough to be considered a tree but has many stems that come out of the ground. It can be taller and has thicker foliage than what is considered a bush. Bushes are typically wild-growing whereas shrubs are more often pruned or shaped.
Rhododendrons originated in Asia, which is where you’ll still find the greatest diversity of the species. However, you’ll find this flowering shrub scattered around the world on nearly every continent.
There are more than 1,000 known species, along with countless hybrids and cultivars. This includes tropical and alpine species that can be either evergreen or deciduous. Depending on the species, you’ll find them in the form of small shrubs and trees rising up to 20 feet or higher.
Azaleas are one of the most well-known subspecies that provide a smaller version of this colorful ornamental. So, if you want a deciduous rhododendron in a warmer climate, an azalea will be your best bet.
Rhododendrons are easily identifiable by their smooth, thick leaves and bright clumps of soft flowers. You’re most likely to find them in shades of red, pink, purple, and white. However, the most common shades are vibrant magenta or fuchsia.
If you want a reliable perennial that attracts pollinators, you’d be wise to pick a rhododendron. This bush is incredibly attractive to hummingbirds, bees, and butterflies. It’s pretty common to walk up to a bush and find a cute buzzing surprise nestled among the petals.
The hardiest Rhododendron varieties thrive in zones 4 through 8. However, as more hybrids and cultivars come into play, gardeners in warmer or cooler zones have more options for what they can plant.
Growing zones are based on a region’s minimum average winter temperature. If you’re unfamiliar with growing zones, here’s a quick breakdown.
Average Temperatures By Hardiness Zone
- Zone 1: -60 to -50 degrees Fahrenheit
- Zone 2: -50 to -40 degrees Fahrenheit
- Zone 3: -40 to -30 degrees Fahrenheit
- Zone 4: -30 to -20 degrees Fahrenheit
- Zone 5: -20 to -10 degrees Fahrenheit
- Zone 6: -10 to 0 degrees Fahrenheit
- Zone 7: 0 to 10 degrees Fahrenheit
- Zone 8: 10 to 20 degrees Fahrenheit
- Zone 9: 20 to 30 degrees Fahrenheit
- Zone 10: 30 to 40 degrees Fahrenheit
- Zone 11: 40 to 50 degrees Fahrenheit
- Zone 12: 50 to 60 degrees Fahrenheit
- Zone 13: 60 to 70 degrees Fahrenheit
So, when we say rhododendrons are hardy perennials in zones 4 through 8, that means most species will tough out a winter that could drop to 3 to 20 degrees Fahrenheit. But, if you want your rhododendron to be a true perennial, you’ll have to make sure the species you pick will handle the winter chill in your zone.
You might be wondering if you can grow them in zones 1 through 3 or 9 through 13. The answer is, it depends. While most species do really well in 4 through 8, only a few thrive in other zones.
For example, the Northern Lights variety can grow in some areas of zone 3. However, you might need added shelter and more specialized care to keep it coming back each year. Unfortunately, you’ll only be able to grow them inside in zones 1 or 2, and maintaining them as a perennial will be difficult.
For warmer climes, you can choose a species that are more accepting of heat. Azaleas are your best option since they tend to thrive in warm weather.
If you’re planting in zones 3 through 6, where the winters tend to be very cold, you should plant in an area that gets a bit more sun. A spot that gets about six hours of full sun is ideal because it’ll help prevent mildew. Also, don’t forget a burlap or lattice windbreak, especially in wind-prone regions.
In warmer zones, you can plant your shrubs in a spot that gets less direct sunlight each day. You also won’t need to worry about a windbreak or winter prep once you get into zones 7 and up.
Dormancy in Cold Weather
A rhododendron’s ability to go dormant in winter is why it makes it such an excellent perennial shrub for your garden. As evergreens, they’re naturally tough. However, even the hardiest of plants can still suffer winter damage.
Once the frost season hits, you’ll probably notice your rhododendrons’ leaves curling in on themselves. This allows them to conserve water, which helps them survive the cold months. You can do a few things to help give their protective nature a boost, though.
First, remember that they have pretty shallow roots, making them very susceptible to frost damage. For that reason, piling on a thick layer of mulch can help insulate those roots from the cold.
You could also consider adding a windbreak made of burlap or wood to protect your shrubs from winter winds. These winds can take precious moisture away from leaves, which means blocking the wind will help prevent that moisture loss.
Maintenance & Care
Rhododendrons are fairly easy to maintain. Since most varieties are hardy, they don’t need much care throughout the year, aside from any trimming or shaping you might want to do.
These ornamental shrubs do really well in shady areas. In fact, they thrive under large trees that are away from direct sunlight. So, for best results, plant yours in a spot that gets a fair amount of morning sun with dappled sunlight throughout the rest of the day.
Before you plant, make sure to test your soil a few months ahead of time. They thrive with a soil pH of 4.5-5.5. If your soil pH is more or less than this, you’ll need to properly adjust it to make it perfect for your plants. You can do this by adding agricultural limestone or sulfur to make it more basic or acidic, respectively.
Another thing to consider when choosing a spot is proximity to paved areas. Sidewalks, pathways, and driveways all leach alkali materials into your soil. Since this can drastically alter the pH, you want to avoid planting perennials too close.
Your soil should also be well-drained. They don’t do well in soil that’s constantly wet. However, since their root systems are pretty shallow, your soil still needs to be moist. If your soil isn’t ideal, you can add compost or peat moss to help with moisture. Or, if that’s not an option, you can choose a raised bed instead.
As perennial shrubs, they can get quite big. For that reason, pick an area that’ll allow for 2-6 feet of growth. This’ll let your plants thrive over the years without roots getting tangled up. Plus, you’ll need the space if you want your bushes to grow to a size where they provide yard privacy.
Like many plants, rhododendrons can fall victim to diseases. However, to keep yours coming back every year, there are some steps you can take to prevent damage.
One common problem is root and crown rot. This is a surefire way to end the life of your shrubs. It’s generally caused by poor soil, which is why it’s so crucial to test and prep your soil months before you plan to plant.
Another prevalent disease is dieback. This fungal infection can cause branches and leaves on your shrubs to die. You can prevent dieback by choosing varieties that aren’t susceptible to the fungus and proper pruning.
Leaf spots are another common problem. Fortunately, these brown spots are mainly an aesthetic problem. However, more extreme cases can cause leaves to drop early and affect your shrub’s health. The best prevention is a fungicide spray and keeping the leaves dry when you water.
Popular Perennial Varieties
- ‘Blue Diamond’ has bluish-purple flowers and grows to about 5 feet. Best in zones 7 through 9.
- ‘Cecile’ grows up to 7 feet and boasts salmon-colored blooms. Best in zones 5 through 8.
- ‘Cunningham’s White’ reaches 4 feet and grows best in zones 5 through 8.
- ‘Purple Gem‘ has purple flowers, will reach about 2 feet, and does best in zones 5 through 8.
- ‘Yellow Petticoats’ reach about 4 feet and thrive in zones 6 through 9.
Rhododendrons are beautiful perennial shrubs that can add depth and color to any landscape. They require little care throughout the year, although some TLC will help keep them strong through the winter. As long as you choose the right option for your growing zone, you’ll have gorgeous blooms for years.