Rhododendron
Rhododendrons and Azaleas are so closely related there is little distinction between the two. The two are addressed separately on this site, even though all Azalea are Rhododendrons. Rhododendrons are typically evergreen but typically thought of as a deciduous shrub. Azalea are typically deciduous. The flowers are also different.
Rhododendron Rhododendron ‘April White’
Hardiness Zones: Zones 4-8
Light Requirements: Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 3-5 feet
Mature Spread: 3-4 feet
Shape: Compact, upright and rounded
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, rich organic soil with peat. Requires acid soil.
Foliage: Glossy dark green evergreen leaves
Blooms: Pure white double blooms
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
Lightly fragrant pure white double blooms grace ‘April White’ in spring. Double blooms are unique among Rhododendrons. Foliage emerges coppery in spring and matures to a deep glossy green. Leaves turn a coppery bronze again in autumn. ‘April White’ is a PJM hybrid, doesn’t get much hardier for northern climates.
The ‘April White’ bush may reach about 3 feet in 10 years time, but will continue to grow over its’ lifespan to 5 feet tall and 4 feet wide. It will not tolerate west soil and is a bit fussy about having rich well drained acidic soil. Mulch heavily in winter in coldest climates.
Rhododendron Rhododendron ‘Milestone’
Hardiness Zones: Zones 4-8
Light Requirements: Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 2-3 feet
Mature Spread: 3-4 feet
Shape: Rounded, Upright
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, organic soil. Requires acid soil.
Foliage: Glossy dark green leaves, maturing to mahogany in winter.
Blooms: Deep pink blooms in spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
Trusses of 3 to 10 deep pink blooms cover ‘Milestone’ each spring, generally in the late spring to early mid season. Autumn will sometimes bring brilliant red leaf color depending on when cold snaps hit, otherwise foliage will turn a lovely burgundy. All in all ‘Milestone’ is a robust specimen with outstanding blooming.
This hybrid, a part of the PJM family, has inherited both heat tolerance and cold tolerance. It does seem to prefer a bit of sun. This very slow grower is ideal for small spaces and foundation plantings where you do not want plants to outgrow the space. ‘Milestone’ is semi evergreen. ‘Milestone’ has previously been known as ‘Marathon’.
Rhododendron Rhododendron x ‘P.J.M.’
Hardiness Zones: Zones 4-8
Light Requirements: Part Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 3-6 feet
Mature Spread: 4-7 feet
Shape: Upright and rounded
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, organic soil. Requires acid soil.
Foliage: Glossy dark green leaves, maturing to mahogany in winter.
Blooms: Lavender pink blooms in early spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
P.J.M Rhododendron is one of the hardiest of the hybrids, developed by the University of Minnesota. It is a small leafed variety that begins its showy blooming at an early age, unlike many Rhododendrons that require a few years to mature before blooming. Glossy rich dark green leaves turn mahogany in winter and holds its leaves most, if not all of winter.
Although preferring part shade, P.J.M is more sun tolerant than large leaf cultivars, but should be protected from burning winter sun. Winter sun and wind can damage the evergreen foliage, so select an appropriate spot (keeping in mind sun and wind patterns are not the same summer to winter). Rhododendrons are shallow rooted and should not be planted too deep and mulch to retain soil moisture. Rhododendrons continue to grow well into autumn and are susceptible to early freeze damage. Water thoroughly until the ground freezes to allow the plant to properly acclimate to winter.
Plant P.J.M. anywhere to add bright color to your spring landscape and rich foliage color in fall. A perfect specimen or accent plant, foundation plant, hedge or lining a fence or walkway. You can expect P.J.M Rhododendron to live as long as 40 years in ideal conditions.
Rhododendron R.carolinianum x dauricum ‘P.J.M. Northern Starburst’
Hardiness Zones: Zones 4-7
Light Requirements: Part Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 4-5 feet
Mature Spread: 2-5 feet
Shape: Upright and rounded
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, organic soil. Requires acid soil.
Foliage: Glossy dark green leaves, maturing to mahogany in winter.
Blooms: Mauve purple blooms in spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
‘Northern Starburst’ is an improved, much more sturdy, variety of ‘P.J.M’. It is an early bloomer, in May, with strong stems. Clusters of intensely colored mauve purple flowers have more substance than the ‘P.J.M.”. Blooms have frilled edges and can be as much as 2 1/2 “ across. Each flower truss holds 4 to 5 flowers.for huge impact.
It has a compact growing habit with leaves that are thick and leathery, turning mahogany in autumn. ‘Northern Starburst’ has a compact dense form with thick strong stems.
Rhododendron Rhododendron x ‘Haaga’
Hardiness Zones: Zones 4-8
Light Requirements: Full Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 4-7 feet
Mature Spread: 4-5 feet
Shape: Upright and mounded
Growth Rate: Slow to Moderate
Soil Preference: Prefers a cool, moist, rich organic soil with peat. Requires acid soil.
Foliage: Glossy dark green evergreen leaves
Blooms: Deep pink blooms in spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
‘Haaga’ is one of the Marjatta hygrids from Helsinki, Finland. It is one of the best large leaf Rhododendrons for the north, bred from a very tough Korean species. ‘Haaga’ is a super hardy upright shrub with dark green evergreen foliage. Dark pink flower buds appear in May and June, and open to a lighter pink with dark streaks. Blooms are lightly scented and blooms reliably even when young.
‘Haaga’ is just a bit fussy about conditions. It must have excellent drainage, mulch and peat moss soil additive. It will not do well in wind. It prefers shade to part shade. Has been successfully grown in zone 3. Plant beautiful ‘Haaga’ as an accent plant, a low hedge, foundation plant, or anywhere spring impact is desired.
Rhododendron Rhododendron ‘Karin Sleger’
Hardiness Zones: Zones 5-8
Light Requirements: Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 1-2 feet
Mature Spread: 2 feet
Shape: Compact mounded
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, rich organic soil with peat. Requires acid soil.
Foliage: Glossy dark green evergreen leaves
Blooms: Purple blooms in spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
Trusses of 5 to 7 vibrant purple blooms cover beautiful ‘Karin Seleger’ in late spring. The dwarf evergreen shrub is very compact and forms a perfect mound of deep green foliage. It grows to a low height of usually only one foot high and spreads to about two feet wide. Morning sun will be enjoyed but shade in the afternoon heat is necessary.
‘Karin Seleger’ is a perfect front of the border or foundation shrub, or with its rich purple color a lovely accent shrub. Don’t let it dry out in heat or drought. In ideal conditions ‘Karin Sleger’ may live up to 30 years while continuing to grow, perhaps to 3 feet tall and wide.
Rhododendron Rhododendron ‘Thunder’
Hardiness Zones: Zones 4-8
Light Requirements: Sun to Part Shade
Water Requirements: Prefers a moist soil and is not tolerant drought periods. Water regularly
Mature Height: 2-3 feet
Mature Spread: 3-4 feet
Shape: Rounded, Upright
Growth Rate: Slow
Soil Preference: Prefers a cool, moist, organic soil. Requires acid soil.
Foliage: Glossy dark green leaves, maturing to mahogany in winter.
Blooms: Deep fuscia purple blooms in spring
Fruit: Insignificant
Disease and Insects: Susceptible to lace bug, leaf spot, chlorosis and winter injury.
Fertilize: Apply acidic fertilizers made for rhododendrons in spring and every 8 weeks, yellowing of the foliage is an indicator of low acid.
Pruning: Prune after flowering
Big round trusses of 3 to 5 purple flowers are breathtaking in spring. The blooms fade to white as they mature. ‘Thunder’ is part of the PJM Group of Rhododendrons, hybridized in 1971 from a seed parent and a pollen parent, producing the rich jewel toned purple of ‘‘Thunder’s” blooms.
A compact shrub with a lovely rounded for, ‘Thunder’ is perfect for any planting bed or as a specimen plant. Like most of the PJM Rhodendrons, there has been much success growing ‘Thunder’ in zone 4.