By: Teo Spengler
Rhododendron shrubs provide your garden with bright spring flowers as long as you site the shrubs in an appropriate location in an appropriate hardiness zone. Those who live in cooler regions need to select hardy rhododendron varieties to be sure the bushes make it through the winter. For tips on planting rhododendrons in zone 5, as well as a list of good zone 5 rhododendrons, read on.
When you are planting rhododendrons in zone 5, you need to recognize that rhododendrons have very specific growing requirements. If you want your shrubs to thrive, you need to take their sun and soil preferences into account.
Rhododendrons are called the queens of the shade garden for good reason. They are flowering shrubs that require a shady location to grow happily. When you are planting rhododendrons in zone 5, partial shade is fine, and full shade is also possible.
Zone 5 rhododendrons are also particular about soil. They need moist, well-drained, acidic soils. Hardy rhododendron varieties prefer soil fairly high in organic matter and porous media. It’s wise to mix in topsoil, peat moss, compost or sand before planting.
If you live in a region classified as zone 5, your winter temperatures can dip well below zero. That means that you’ll need to select rhododendrons for zone 5 that can survive. Fortunately, the Rhododendron genus is very large, with 800 to 1000 different species – including the entire azalea clan. You’ll find quite a few hardy rhododendron varieties that will do well as rhododendrons for zone 5.
In fact, most rhododendrons thrive in USDA hardiness zones 4 to 8. If you are pining for azaleas, you’ll have to be a little more selective. Some thrive down to zone 3, but many don’t grow well in such cold regions. Avoid species that are borderline hardy in favor of plants hardy to zone 4 if possible.
You find some top choices for zone 5 rhododendrons in the Northern Lights Series of hybrid azaleas. These plants were developed and released by the University of Minnesota Landscape Arboretum. Northern Lights rhododendrons are not just borderline zone 5 rhododendrons. They are hardy in regions where temperatures drop to -30 degrees to -45 degrees Fahrenheit (C.).
Take blossom color into account when you are picking zone 5 rhododendrons from the Northern Lights series. If you want pink flowers, consider “Pink Lights” for pale pink or “Rosy Lights” for deeper pink.
Rhododendron “White Lights” produce pink buds that open to white flowers. For unusual salmon colored flowers, try “Spicy Lights,” a shrub that grows to six feet tall with an eight-foot spread. “Orchid Lights” are zone 5 rhododendrons that grow to three feet tall with ivory colored flowers.
While Northern Lights are reliable as zone 5 rhododendrons, your selection is not limited to this series. A variety of other zone 5 rhododendrons are available.
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RHODODENDRON ORBICULARE: Thrives in the cool summers and mild winters at the RSBG. Native to the remote misty mountains of the Wolong Giant Panda Reserve in Sichuan, China, where it flourishes deep in the forests alongside bamboos. Photo by: Andrew Drake.
For diversity of size, form, foliage and flower color, it is hard to imagine any other group of plants matching rhododendrons and azaleas. We all know about the spectacular garden hybrids with their blinding colors and huge flower heads. But there is another remarkable group known as species rhododendrons, wild plants found growing naturally in the forests and mountains of the world, many of which make outstanding garden plants. One of the best places to see them is the Rhododendron Species Botanical Garden in Federal Way, Washington, which contains one of the largest collections of rhododendrons worldwide.
AppealThousands of variations with a virtually unlimited palette of floral color blooming from late winter into late summer. Some types are fragrant. The foliage of many species is extremely unusual and attractive, providing year-round interest.
ZonesEasy to grow in cool-summer/mild-winter regions, Zones 5 to 9. Outside of these regions, it is still possible to grow many kinds if care is taken to select the appropriate cultivars or species. The RSBG is considered Zone 8.
ExposureIn general, rhododendrons require a bright but not-too-hot exposure with low soil temperatures. Exceptions are the tiny-leaved alpine and dwarf species, which are best in bright sun.
RHODODENDRON DAVIDSONIANUM AND R. AUGUSTINII: Two of the finest and easiest species to grow in their color classes, the deep pink of the former contrasts brilliantly with the lavender blue of the latter. Photo by: Andrew Drake.
SoilExcellent drainage in an organic woodland soil or in a sandy soil that has been amended with bark or other organic matter. In heavier and clay soils, plant in raised beds.
CareWater through dry periods. Regular mulching with organic material means extra fertilizer is usually unnecessary. If the plants seem unhealthy, it is usually because of poor drainage.
Read on to discover a collection of wild rhodies that make outstanding garden plants:
Easy in sun or shade, this species is slow-growing enough to cultivate as a specimen in a large container.
Large-growing species with lavender-blue flowers, suitable for sun or shade. It can be selectively cut back to reduce its size. Selected forms have flowers closer to true blue than almost any other rhododendron. Hardy to 0 degrees.
Famous flame azalea native to the forests of the Appalachian Mountains. Brightly colored blossoms occur naturally in blazing shades of red, orange and yellow. Tough, hardy, deciduous species well-adapted to gardens, performing beautifully in sun or light shade. Hardy in Zones 5 to 8.
RHODODENDRON DEGRONIANUM SSP. YAKUSHIMANUM
A perfect garden plant and probably the most popular and widely grown species in the world. Native to Japan with a dwarf mounding habit to 3 feet, foliage that is densely hairy or “indumented” on the leaf undersides and perfect apple-blossom-pink flowers fading to pure white. Used extensively in hybridizing programs. Relatively cold and heat tolerant. Hardy to -15 degrees.
Extremely variable, native to Japan, and, like many plants from that region, it is well-suited to cultivation in East Coast gardens. The pale yellow flowers of the larger growing forms shine in the woodland garden, while a diminutive selection known as ‘Yaku Fairy’, from the mountainous island of Yaku Shima, is the perfect dwarf for a rock or trough garden.
Vigorous and bushy, native to Sichuan, China, extremely floriferous. Does not require the removal of spent-flower trusses-known as deadheading. Lovely flowers range in color from pale pink to lavender or mauve, often with dark red spots. Hardy to about 0 degrees.
Always attracts attention with its smooth round leaves and rose-to-pink bell-shaped flowers. Best in light shade to maintain the mounding habit and avoid foliage scorch. Hardy to -5 degrees in maritime climates.
One of the best of the dwarf or “alpine” rhododendrons for the rock garden. Easily grown in a sunny location with excellent drainage, this species forms a dense mound to 3 feet with striking blue-purple to reddish-purple flowers. Native to southwest China. Hardy to -15 degrees.
Variable species native over a wide area of Japan, with different forms occurring on virtually every mountain range in the southern half of the island chain. Lower surface of the leaves is coated with a dense furry layer of hairs known as the indumentum, adding welcome color and interest in the nonblooming season. Pink to rose or rarely white flowers appear in late spring, and the plants are quite adaptable in most climates, even tolerating the heat and cold of the East Coast and upper Midwest if provided with proper shade and care. Hardy to -15 degrees.
Deciduous azalea, outstanding as an ornamental for a sunny border or woodland edge. Bright yellow flowers are delightfully fragrant, and autumn foliage brings a bright red splash of color. A clone selected at the RSBG known as ‘Golden Comet’ is an especially fine form with a much larger inflorescence of deep yellow flowers and good resistance to the common, disfiguring but relatively harmless powdery mildew that so often afflicts azaleas. Hardy to -10 degrees.
Looking for an evergreen shrub that loves the shade, bears large flowers, is low maintenance and will last for decades? Then look no further than the hardy rhododendron.
It's best to plant your rhododendrons in spring or early fall. If your soil is fertile, you probably won't need to fertilize them. Otherwise, feed them with a product labeled for azaleas and rhododendrons and follow the package directions for how much to apply and how often. Torn between azaleas and rhododendrons for your landscape? Both kinds of shrubs are in the Rhododendron genus and thrive in well-drained, acidic soils, although rhododendrons are usually bigger plants with bigger leaves and flower clusters, also called trusses. For best results, plant rhododendron varieties recommended for your region.
'Dandy Man Color Wheel', shown here, spins through four colors: lipstick-red buds and ruffled blooms that open to soft pink inside and deep pink outside. The fourth color? The flowers age to pure white before they drop. The plants, which are hardy in USDA Zones 5-9, hold their leathery leaves throughout the winter. They're also deer resistant and take part sun to sun. They grow from 48 to 96 inches tall and wide and make good hedges, border plants or specimen plants.
Bright lavender-purple blooms and dark green leaves make 'P.J.M.' rhododendrons show-stoppers. This variety is hardy in Zones 4-8 and attractive even in winter when its evergreen foliage takes on a mahogany-brown tint. Try it in borders, mass plantings or containers.
Despite its name, 'September Song' opens its loose, showy clusters of orange, pink and yellow blooms in spring. This evergreen shrub is hardy in Zones 6-8 and works beautifully as a foundation plant or in a mixed border. It grows at a moderate rate to reach four to five feet tall, with a wider spread, and, like most rhododendrons, it's easy to care for. Plant it with camellias, gardenias, azaleas or coral bells. Give it partial sun and regular water, especially if you're in a warm region or if it's planted in a container.
With pink buds that open to ruffled pink blooms, 'Southgate Brandi' is a heat-tolerant, evergreen rhododendron for Zones 6-9. This petite shrub stays small, maturing at around three to four feet tall and wide, so it's ideal for containers or growing along the edge of a path or walkway. Give it part sun to full shade. It has good resistance to pests and tolerates heat. The leaves remain on the plants and stay colorful in the winter. 'Southgate Brandi,' like most rhododendrons, doesn't need much pruning, but if you do want to trim it, it's best to do so just after the flowers fade in spring.
Bright red flowers make 'Nova Zembla' a winner in the garden. Hardy in Zones 4-8, this small, evergreen rhododendron can become deep pink in sunny areas. It needs partial sun and regular watering, but you'll probably need to water weekly or more often when the temperatures climb. Thanks to its upright, dense growth habit, 'Nova Zembla' can be grown as a privacy screen or hedge, and it works equally well when planted in masses or in a mixed border. This showy shrub needs lots of room, maturing at five feet tall and wide. Hollies, hydrangeas, astilbes and coral bells are good companion plants.
Need a flowering shrub for a small space? 'Amy Cotta' fits the bill. This semi-dwarf shrub has ruffled, pink-lavender blooms and grows to two or three feet tall and about three to four feet wide. It prefers part to full sun and is hardy in Zones 4-9. This evergreen rhododendron has azalea-like leaves and slowly grows into a mounded form, so it’s fine for planting around foundations or in a mixed border or woodland garden. Be conservative if you prune it. A light trim is usually all it needs and make sure you prune in the late spring after it blooms.
'Black Hat' is a very early spring bloomer with bright purple ruffled flowers and deep purplish-green, leathery foliage. Hardy in Zones 4-8, this small shrub holds its leaves year-round. Expect it to mature at just 36 inches tall and wide, so try it in a small garden spot or a container. Give it part sun to sun and prune lightly, if at all. Try 'Black Hat' in a border or in masses and enjoy the color changes that cold weather brings when the foliage becomes very dark green with hints of purple and black.
This plant with a yummy-sounding name has blooms that you could describe as decadent. The ruffled, dark pink and white flowers have red margins and a deep-red smudge on each upper lobe. Hardy in Zones 5-7, 'Cherry Cheesecake' is an evergreen with a slow, mounding growth habit in time, it reaches four to five feet tall and wide. Plant it with hydrangeas, bleeding hearts (Dicentras) or coral bells in partial shade to partial sun, where it will often attract birds and butterflies. It's excellent as an accent plant or in a hedge, woodland garden or container.
'Chionoides' blooms in mid to late spring, so you can use it to extend your flower show if most of your rhododendrons are early bloomers. Each large, round flower cluster can contain over a dozen bell-shaped white blooms splashed with yellow. The plants are compact and dense, growing an average of four feet tall and four to six feet wide, so they're great for planting in an informal hedge or along a foundation. This evergreen shrub takes part shade to full sun and is hardy in Zones 5-9. It's easy to grow, but like most rhododendrons, water it regularly and often in hot weather or if it's in a container.
Vigorous 'Roseum Elegans' is an evergreen rhododendron prized for its large, rose and lilac-colored flowers. This late-spring bloomer likes partial sun and is recommended for Zones 4-8 it doesn't mind cool temperatures but its large, broad leaves need some protection from harsh winter winds. It can reach six to eight feet tall and wide, so give it plenty of space in a woodland garden or naturalized area. It also makes an attractive specimen plant.
Some rhododendrons are more adaptable to shade during any season. The P.J.M group of rhododendrons are some of the most reliable shade bloomers. Because they do not develop seeds, the energy goes directly toward producing flowers. Within this group are varieties with pink-to-lavender blooms such as Elite and Waltham. Henry's Red is the color its name implies. The true red flowers have even deeper red eyes that appear almost black. A choice white P.J.M rhododendron for shade is Molly Fordham. The petals are much sturdier than most white flowering shrubs, so they hold up well to spring rain. These are particularly cold-tolerant selections, hardy to USDA zone 5.
I spotted some "dwarf rhododendrons" at my favorite nursery. Would I be able to grow these rhododendrons in a pot, and would they need any special care?
Answer: Whether you are limited on space or just want to add detail and focal points to a certain garden area, container gardening is a wonderful way to create spectacular showcases for favorite plants.
Rhododendrons, with over 1,000 varieties in an abundance of breathtaking colors, are great for adding often-evergreen appeal. With the right care, they can thrive beautifully in containers.
Here are a few tips on how to successfully grow rhododendron in containers:
• Choosing the right container: When selecting the right pot, you must take into consideration the size of your rhododendron because the size of the plant and the size of the container go hand in hand. A good rule of thumb is that if you have purchased a rhododendron from a nursery or garden center, choose a pot that is about a third larger than the original container your rhododendron came in. The key factor in container selection is to make sure there are lots of drainage holes. Rhododendrons can often fail when grown in pots due to poor drainage. (Try using pot feet to not only keep your wooden floorings safe but to also keep your plants from sitting in excess water.) lastly, rhodies are shallow rooted, so they may like a wide, shallow pan rather than a tall, narrow pot.
• Soil: Once you have selected the right container, plant your rhody with a potting mix formulated for azaleas, which will be at the acidic pH that rhododendrons love. Make sure to set the shrub so it sits at the same level it did in its previous container, or even a bit above that level (in relation to the surrounding potting mix). Rhododendrons prefer this position they do not want to be planted deep. Do not fill all the way to the top of the container. You want to make sure to leave a few inches at the top so you can apply a thin layer of compost, shredded leaves or mulch around the base of the plant to help lock-in moisture. Reapply as this layer becomes depleted.
• Maintenance: Place the container in a location with lots of indirect sunlight, part shade or dappled shade—somewhere that the plant has access to the sun but without risking the flowers and foliage of becoming scorched and damaged. Make sure to water rhododendrons thoroughly when the soil feels dry to the touch. Apply fertilizer for acid-loving plants, like HollyTone, every spring to help encourage growth. Remove any spent/wilted flowers. Repot every 1 to 2 years.
• Plant selection: Choose a dwarf variety that thrives in your climate for the best results—try to keep within 3 to 5 feet in height. Shrubs (and other plants) in containers should be rated to at least one cold-hardiness zone colder than yours. For instance if you live in USDA Zone 6, choose a variety that's hardy to at least Zone 5. Otherwise you should offer winter protection. Some popular dwarf selections include: most yaks (R. yakushimanum cultivars), Rhododendron lutescens and ‘Ostbo’s Red Elizabeth’.
If you are considering growing rhododendrons, the first step is to test your soil for its acid/alkaline balance. If your neighbours are growing these plants successfully you can assume they will grow for you, but otherwise a soil-test kit can be found cheaply at any garden center or hardware store.
It just takes a few minutes to test your soil and if it is less than 5.5 on the pH scale, you are set to go as a rhodo grower. If your soil is pH7 or less you can still grow these plants, but it is a good idea to get some chelated iron and apply it every spring before new growth begins. No matter what your soil, if your plants have yellow new leaves or leaves that are light-green with darker-green veins, use chelated iron on them.
If your soil is more than pH7 you may still succeed, especially with the Lavender Rhododendron or with the Nova Zembla Rhododendron if you use the chelated iron once or twice a year and if they do well then you could try some others as well. However with their fine root-systems rhododendrons do well in planters, so pick up some potting soil for acid-loving plants and some of the same kind of fertilizer too and you can have a beautiful rhododendron season no matter what your soil is.
The less acid your soil, the more important soil preparation will be for these plants. Digging plenty of peat-moss into the planting area is the first step. Well-rotted leaves are also a good soil addition. After you plant mulch the area with a layer of peat or leaves two or three inches thick and renew the mulch annually in early spring.
When planting, dig a hole that is three times the width of the pot and just a little deeper and plant at the same depth as your plant was in the pot. Rhododendrons should not be planted deeply at all. Use plenty of water during planting – a good trick is to only put back part of the soil, flood the hole with water and put the rest of the soil back when it has all drained away. The lower levels of the soil will now be nice and moist.
The best of the many "PJM" cultivars available. In early spring this small-leaved evergreen shrub is covered in a profusion of deep red-purple flowers – definitely a harbinger of the season! The aromatic foliage often changes to almost a mahogany color when the temperature becomes colder and provides striking wintertime interest. Reaches roughly 5 feet tall.