Azaleas & Rhododendrons 4/23/21

RHODODENDRONS & AZALEAS

Tony Fulmer

“Large leaf” Rhododendrons

·         Rounded, generally as wide as tall

·         Moderate numbers of large flower clusters in May – June

·         Growing season: Prefer half day sun, half day shade

·         Winter:  Avoid full sun and open northwest winter wind

·         Moderate growth rate

“Small leaf” Rhododendrons

·         Broad vase shape, taller than wide

·         Large numbers of smaller flower clusters in April-May

·         Growing season:  Full sun to ¾ shade

·         Winter: Will tolerate some winter sun & wind

·         Moderate growth rate

Evergreen Azaleas

·         Semi-evergreen

·         Flat-topped, rectangular, wider than tall

·         Large numbers of flower clusters throughout the plant in May

·         Growing season:  Prefers ½ day sun, tolerates shade

·         Winter: Avoid full sun and open northwest wind

·         Slow growth rate

Deciduous Azaleas

·         Broad oval to vase shape

·         Moderate numbers of flower clusters at ends of branches in May-June

·         Growing season:  Full sun or ½ day shade

·         Winter:  Sun or shade, winter wind acceptable

·         Moderate to fast growth rate

THE CARE & FEEDING of RHODODENDRONS & AZALEAS

Site – Avoid planting under black walnut due to juglone toxicity ½ sun (AM preferred)

• ½ day sun (AM preferred), ½ day shade during growing season. Larger the leaves, the more shade that’s require
• Well-drained (NEVER wet or boggy), coarse, highly organic soil
• Avoid hot box sites (where summer temps can rise above 90° F.)                   
• Avoid open, windswept northwest winter wind-facing sites (most important for large leaf rhodies) OR against open south winter walls where reflected heat can cause wild winter temp swings

Soil Preparation

• Soil must be acidified, ideally to a pH of 4.5-5.5
• Must be coarse, high in organic matter and well-drained.
• Create an artificial mix that will be used to plant - 2 parts shredded pine bark, 1 part topsoil, 1 cup sulfur.
• Do not use peat moss (unless your soil is quite sandy and dries out very rapidly).

Planting

• Remove plant from container and presoak for at least 5 minutes
• to wet root ball.
• If roots are tangled, make vertical slits. Even if roots are not tangled, “rough up” soil ball. White root tips should be showing all over the root ball.
• Dig a shallow depression 2-3 times wider than the diameter of the root ball.
• Incorporate the pine bark/topsoil/ sulfur mix into this hole.
• The root ball should be 1/3 to ½ above the finished grade.
• Fill ½ way with the bark/topsoil mix, then water.
• Mound the balance with bark/topsoil mix so that the top of the root ball is even with the surrounding grade. Water.
• If top heavy, may need to “spearstake” until plants are established.

Mulching

• Buffers soil temperatures year ‘round, reduces weeds and soil compaction, retains moisture, and adds organic matter as it decomposes.       
• We recommend: shredded pine as the very best mulch for acid-lovers. Second choices: Pine needles, shredded leaves or organic compost.   Place mulch 2-3” deep, but never touching trunk or stem tissue.
• Extend the mulch at least to the dripline, and well beyond is better.
• Replenish as needed to maintain a consistent level.

Watering

·         Water deeply and then allow the plants to dry slightly between watering, especially if they are in shade.

·         Hand watering with a watering wand or similar device is preferred. Concentrate on watering the soil ball the first year and less on the surrounding soil.

·         Sprinkler systems are NOT an appropriate way to water rhododendrons and azaleas.

·         Avoid flooding. Of the 4 classes, deciduous azaleas are the most tolerant of “wet” sites.

Fertilization

·         An organic granular fertilizer like Espoma’s “Holly-Tone” (3-4-4 plus 5% sulfur) is a great non-burning choice @ 1 cup per plant.

·         Avoid applying quick acting water-soluble fertilizers before bloom as they may cause flower buds to abort.

·         Avoid high nitrogen fertilizers, especially for plants located in deep shade- This will encourage foliar growth at the expense of flowers.  

·         Apply ½-1 cup of sulfur per plant annually (any time of year since it is not a fertilizer, but an acidifying agent). Mulch must be pulled back and sulfur applied directly to the soil surface.

·         Avoid fertilization after mid-July to allow plants to harden properly.

 

Pruning/ Deadheading

• Light pruning (for shaping) should be done right after flowering as soon as the new leaf and stem growth has expanded. Cuts should be made immediately above a set of leaves.
• Deadhead large leaf rhododendrons and deciduous azaleas as the flowers fade. Hold the stem under the flower with thumb and forefinger, gently snapping the spent flower head off.
• Small leaf rhododendrons and evergreen azaleas tend to be prolific, so deadheading can be time-consuming and tedious.
• If you have the time and inclination, do it as you will be rewarded with more bloom the following year.

Disappointing/ or no bloom?

• Plants are too young or not well established.
• Too much nitrogen, excessive foliar growth.
• Too much shade.
• Profuse bloom previous year (mainly large-leafed rhodies and deciduous azaleas), but not deadheaded.
• Cold temperature damage in the winter.
• Any combination of the above.

Winter Care

• Apply ¼ cup superphosphate after September 1 to maximize winter hardiness.
• If the fall is dry continue watering regularly so plants are well hydrated, whether they are established or new.
• Top mulch off if it has decomposed or otherwise disappeared.
• Apply antidessicants to evergreen types, esp. large-leaf rhodies.

Large leaf Rhododendrons:

• ‘Capistrano’ - 5’, 5’- Frilly clear yellow flowers, very dark green foliage. -15° F.     
• Midseason
• ‘Haaga’ – 4’, 4’ - Wavy-edged, deep purplish-pink. Really flower bud hardy to -29° F.                                      
• Late
• ‘Janet Blair’ – 6’, 6’ - Pale mauve-pink, fragrant. Nice plant habit. -15° F.
• Mid-late
• ‘Nova Zembla’ - 5’,6’ Dark red with black throat markings. Glossy leaves. -25° F.
• Mid.
• ‘Scintillation’ - 4’,5’ Purplish-pink with wavy edges. Great foliage plant. -15° F.
• Early-midseason
• ‘Spring Dawn’- 6’, 4’ Rounded, rosy-pink with yellow throat blotch. Dense, vigorous plant. -20° F.
• Midseason.

Small leaf Rhododendrons:

• ‘Olga Mezzitt’ – 5’, 5’ Peach flowers bloom 7-10 days after ‘PJM’. Dark reddish fall/winter coloration. -25° F.
• Early-midseason
• ‘PJM’- 5’, 5’ Lavender-purple flowers. Nice green summer foliage, mahogany-purple fall/winter color. -25° F.
• Early
• ‘PJM Elite’- 5’, 5’ Pinkish-purple flowers, slightly pink being the differentiator from ‘PJM’. Mahogany fall color, too. Slightly taller, faster growing than ‘PJM’, last to bloom. -25° F.
• Early.
• ‘PJM Landmark’ – 5’, 5’ Deep rose pink to the point of being almost red. Opens deep, deep pink. Glossy foliage is mahogany over the winter. -25° F.                                                        
• Early
• ‘Planeview Appleblossom’ – 5’, 5’ A pale pink branch sport of ‘PJM’ that blooms at the same time!
• ‘Sugar Puff’ -3’, 3’ Pale, pale pink buds open to soft white with a hint of pink at the edges. Fine-textured foliage with nice reddish-brown stems. -15° F.                                                    
• Early-midseason.

Semi-evergreen Azaleas:

• ‘Bixby’- 2’, 3’ Deep rose-red flowers in tight clusters. Mushroom-shaped plant with small dark green leaves. Almost black in winter snow. -20° F.                                                        
• Midseason.
• ‘Elsie Lee’ - 3’, 3-4’ Semi-double pink flowers with lilac undertones. Plant is upright, but broad.
• Midseason.                       
• ‘Herbert’ - 3’, 4’ Dark purple-pink, “double” flowers with a dark throat blotch and ruffling. -10 F.
• Early-midseason.
• ‘Karens’- 4’, 4’ Bright lavender-purple in clusters. Unusually flower bud hardy, plant is tolerant of alkaline soil. Lower leaves drop off over the winter, with the leaves right under the flower buds persisting. -25° F.                        
• Midseason.
• Poukhanense compacta (Dwf. Korean azalea) – 3-4’, 4-5’ Pale lilac-orchid flowers are spotted on upper petals. Flowers are lightly fragrant. May assume orange and red fall color in sunny sites, but quite shade tolerant. -18° F.
• Midseason.

Deciduous azaleas:

• ‘Gibraltar’ - 4’, 5’ Large, fragrant flowers of intense orange with frilled edges. Great fall multi-color potential when grown in full sun. -25° F.  
• ‘Mt. St. Helens’ – 3’, 4’ Multi-colored coral, pink and yellow with a large yellow throat blotch, lightly scented. -25° F.                                                                    
• Northern Lights – A series bred specifically for their flower bud hardiness which reaches -35° F. More upright and vase-shaped than spreading, good fall            color potential when grown in sun. Also, tolerates alkaline soils.

• Examples: ‘Northern Hi-Lights’ 4-5’, 4’ Creamy white with bright                yellow upper petals.
• ‘Tricolor’ – Deep rose buds open soft pink with white overtones and a yellow throat blotch.
• ‘Pennsylvania’ - Aka ‘Weston’s Pennsylvania’ 5’, 5’ Summer-blooming in July/August with pink flowers that have an orange blotch, good fragrance. Copper-yellow fall color. Hybrid with native parents, one of which is               
• Swamp Azalea. Compact plant habit and powdery mildew resistant. -20° F.
• Swamp azalea – R. viscosum. 4’, 4’ White/very pale pink fragrant late spring/summer flowers. Potential for yellow, orange, purple fall color. Loose, upright shrub great for naturalizing in wet soils.
• Swamp azalea ‘Pink Mist’ 5’, 5’ White flowers tinged with the faintest hint of pink in June-July. Powdery mildew resistant. -20° F. 
• ‘Weston’s Innocence’ – 5’, 5’ Sweetly scented, small white flowers in early summer (July). Mildew-resistant. Burgundy red fall color. Hybrid with parents: Swamp & Sweet Azalea.  -20° F.