Sweet Azalea (Rhododendron arborescens), also known as Smooth Azalea, is a native perennial shrub from the Ericaceae family, originating in eastern North America. This woody plant typically reaches heights of 1.5 to 1.8 meters and is celebrated for its fragrant, lily-like white flowers that bloom in summer, attracting butterflies and hummingbirds.
The plant’s funnel-shaped blooms make it a standout in any garden, while its green foliage transitions to a striking reddish-purple in the fall, adding seasonal interest. Thriving in full sun to partial shade, Sweet Azalea prefers moist, humus-rich soil, making it a versatile and beautiful addition to a variety of garden settings.
| Common name | Smooth Azalea, Sweet Azalea |
| Botanical name | Rhododendron arborescens |
| Family | Ericaceae |
| Species | arborescens |
| Origin | Eastern North America |
| Life cycle | Woody |
| Plant type | Native Plant |
| Hardiness zone | 4, 5, 6, 7 |
| Sunlight | Full Sun |
| Soil condition | Sand |
| Soil ph | Acid |
| Drainage | Well-Drained |
| Growth rate | Fast |
| Spacing | 12 – 24 ft. |
| Harvest time | Fall |
| Flowering period | Spring |
| Height | 8 ft. – 20 ft. |
| Flower color | Gold, Yellow |
| Leaf color | Green |
| Flower benefit | Fragrant |
| Garden style | Butterfly Garden |
| Uses | Naturalized Area |
I. Appearance and Characteristics
Rhododendron arborescens, also known as smooth azalea or sweet azalea, is a species of flowering plant in the family Ericaceae, native to the eastern seaboard of the United States.
It generally blooms in late spring and early summer. The name “sweet azalea” refers to its sweet aroma.
The official credit for the discovery of R. arborescens goes to Frederick Traugott Pursh and John Bartram. It was first observed in John Bartram’s garden in Philadelphia as well as Blue Mountain, Pennsylvania.
It has also been mentioned that the plant was initially noticed by André Michaux in 1795 in the state of North Carolina. However, after further investigation, no more species were found in his conservatory. Therefore, the recognition for the discovery of the plant was given to Frederick Traugott Pursh and John Bartram.
Rhododendron arborescens was first named Azalea arborescens by Pursh in 1814. However, John Torrey renamed it Rhododendron arborescens in 1824 because he believed that it should not be taxonomically separated from the rhododendrons.
Rhododendron arborescens is a deciduous shrub up to 18 ft (5.5 m) tall, with terminal inflorescences growing from the end of the stems. These plants also generally have yellowish-brown twigs. The green, waxy leaves are 1.75–3 in (4.4–7.6 cm) long, oval and entire with round tips and hairy midribs. Plants found at higher altitudes are generally smaller with smaller leaves. The plant produces from 3 to 7 flowers after a white or blue shade has appeared on the leaves. The stigmas are quite visible all the way up to the petals.
The flowers are also known to contain poisonous substances and must not be consumed by humans. The effects of consuming this plant include depression, vomiting, diarrhea, difficulty in breathing, and most dangerously coma.
R. arborescens grows best in soil that is slightly acidic at a pH of 5.5-6. It does not grow well in excessive water and drainage is necessary for healthy growth. It is tolerant of full sunlight but must not be overexposed. It is beneficial to plant it with the roots slightly above the ground and accumulating soil up to the plant roots. Organic matter such as sawdust and pinebark may aid the growth of the plant. Depositing a few inches of pine bark or wood chips may help in keeping moisture and preventing weeds from growing around the plant. However, mature R. arborescens do not need to be fed with fertilizer.
This plant has gained the Royal Horticultural Society’s Award of Garden Merit.
II. How to Grow and Care
Sunlight
Rhododendron arborescens need ample protection from wind and direct afternoon sun. Do not plant them in windy spots. Around buildings, they do best on the east or north side. In open areas, they like alternating sun and shade. Plants may survive continuous shade if trees have branches pruned high. Fences, shrubbery, or screens may also give protection from afternoon sun.
Temperature
In spring and summer, the ideal temperature for growth is 18–22 ° C. In autumn and winter, these plants goes to a rest period which last 1.5 – 2 months with a temperature of 12–15 ° C. Winter damage may occur at infrequent intervals, usually due to lack of dormancy in the plant when cold weather occurs. To help develop winter hardiness, avoid adding large amounts of nitrogen after July.
Watering
Azalea arborescens need ample water during the summer. If they are planted under wide eave overhangs, furnish water during the entire year. Keep in mind that although these plants need moisture, they will not thrive in wet, poorly aerated soils.
Use mulches to control weeds, conserve moisture, and provide more uniform soil temperatures. Mulches can be made of sawdust, bark dust, peat moss, straw, or other organic materials. If these materials are incorporated into the soil after serving as a mulch, add some nitrogen to assist in decomposition of the woody materials.
Avoid excessive irrigation in fall. Plants kept dry in September will tend to harden off and be better prepared for the winter. If the fall has been excessively dry, watering should be done after the first killing frost. At that time watering will not reduce winter hardiness but will prepare the plant for winter. The soil should be thoroughly moist before cold weather sets in. The best time for fall watering is about Thanksgiving.
Soil
Sweet azalea enjoys rich, loose, and slightly acidic soil. Because the plants do not like too much accumulated water, the soil must be well-drained. Leaf mold, pine needle mulch, peat soil, or fully decomposed groundwood are good choices. These are all acidic culture mediums with strong draining ability. Alkalic or sticky soil cannot be used.
These plants are suited to soil with a pH of 4.5-6. Before planting, it is best to test the pH level of your soil. If it is slightly alkalic, you can moderately add an acidic fertilizer like aluminum sulfate. Mix it with the original soil, and ensure the soil is within the suitable pH range before planting sweet azalea.
Fertilizing
Avoid the excessive use of lime or alkaline fertilizers around azalea and rhododendron plants. If necessary, apply nitrogen fertilizers or mixtures (either organic or inorganic) containing nitrogen, phosphorus, and potassium soon after flowering in the spring. Relative merits of an organic fertilizer as compared to a chemical fertilizer depend on whether the slow availability and less frequent application of the organic type can justify the extra cost. A light application of a fertilizer formulated for acid-loving plants may be added to the surface before the mulch is applied. Fertilizing should be done in April or May, but don’t fertilize after July. Late summer fertilization may force out tender fall growth that will be killed by the winter.
Planting Instructions
Sweet azalea is suited for planting in spring or fall. As a shrub, it takes a long time for the seeds to grow. Therefore, it is best to purchase seedlings or potted plants. If they are planted in the garden, make sure the distance between plants is 61 cm. Dig a planting pit with a diameter of three times that of the root ball of the sweet azalea. The roots cannot be buried too deeply, and the root crown should be level with the ground. When the planting pit is half-filled with soil, water it once. When filling is completed, water it again.
Pruning
If new plants are selected properly, taking into consideration mature plant size and space to be filled, little pruning should be necessary. Remove dead and injured branches. If pruning is necessary, prune the plants soon after flowering to allow flower bud formation for the following year. “Dead-heading” is a pruning operation that involves removing spent flower clusters. It should be done annually.
The plants’ form can be improved by pinching out the soft, new shoots of vigorous growing plants. Do not pinch after July because flower buds will not have time to develop for the following year.
Propagation
Rhododendron arborescens can be propagated by air layering or stem cuttings. They can self-propagate by sending up shoots from the roots. Sometimes an attached branch that has dropped to the ground will root in damp mulch, and the resulting rooted plant then can be cut off the parent rhododendron. Cuttings may be made at any time, but June to July cuttings seem most ideal for rooting azaleas, and August to September cuttings seem best for rhododendrons. Make cuttings 3 to 4 inches long, remove lower leaves, and place the cut end in the rooting medium. Equal parts of peat moss and clean sharp builder’s sand make an ideal rooting medium. After roots are formed, place the plants in pots or in a protected area and keep well watered.
III. Uses and Benefits
The sweet azalea’s most prominent feature is its abundance of showy flowers that grow in the summer, although its fall foliage is also stunning. This bushy plant makes a great ornamental hedge or screen in coastal and cottage gardens, and the blooms also draw in butterflies. It is resistant to rabbits but susceptible to deer.
IV. Harvesting and Storage
Collect the flowers of sweet azalea for cut flowers, focusing on ones that have not yet fully bloomed. These flowers are both more beautiful and can be enjoyed for a longer period of time. Use a sharp knife to cut the bottom of the branch diagonally; this increases the area where the cut flower can absorb water. To extend bottle life, do not let the flowers receive direct sunlight. Change the water frequently and cut the bottom of the cut flower obliquely when changing water.
Find Where to Buy the Best Smooth Azalea (Rhododendron arborescens)
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