Posts Tagged ‘Rhododendron indicum’

Rhododendron simsii

Common name: Indian Azalea, Sims’s Azalea

Family: Ericaceae

Synonymous: Azalea indica var. simsii
Rhododendron breynii
Rhododendron danielsianum
Rhododendron decumbens
Rhododendron hannoense
Rhododendron indicum
Rhododendron lateritium
Rhododendron macranthum

Rhododendron simsii

Rhododendron simsii

Distribution and habitat: Rhododendron simsii is native to East Asia, where it grows at altitudes of 500–2700m (1600-9000 feet). It is a shrub that grows to 2m (6.5 feet) in height, with leaves that are ovate, elliptic-ovate or obovate to oblanceolate. Flowers range from white to dark red.

Description: Rhododendron simsii is of the two species of Rhododendron that can be grown as indoor plants. Rhododendron simsii grown indoors are almost invariably hybrids of mixed parentage and are all small shrubs rarely more than 45cm (18 inch) in height and spread and they have 2-3cm (0.8-1 inch) long leathery, generally egg-shaped leaves. Funnel-shaped flowers are borne at the ends of the stems.
Rhododendron simsii hybrids are the large-flowered specimens. The leaves are sometimes glossy, but practically all varieties have some bristly hairs on leaf margins. Flowers are carried in small clusters of two to five; each flower is 4-5cm (1.5-2 inch) across and may be single or double, sometimes with ruffle petals. The colours of flowers are white, magenta or any pink shade and sometimes they are attractively bicoloured. Their flowers are often lasting several weeks. With proper care, Rhododendron simsii in bud stage can give up to six weeks of enjoyment. Rhododendron simsii in bloom provide two to four weeks of beauty.

Houseplant care: These hybrid forms are usually grown indoors for a single season as temporary winter and early spring flowering plants, but it is possible to keep them alive and attractive for several years under the right conditions. It is useful if the plants can be taken outdoors for a few months each year on a well lit verandah or balcony. In their natural state they will flower in mid-spring, but commercial growers generally start batches of plants into growth at different times to produce a succession of well budded plants that will bloom at various periods from early winter well into spring.

The larger the plant, the more easily it is carried over into another year. Most young specimens have been removed prematurely from nursery beds, have had their roots pruned and have been packed into small pots. Thus, often they cannot tolerate the treatment that is necessary for them to continue growing and flowering in subsequent years.

Light: Potted Rhododendron simsii in bud or bloom should be placed in bright light but out of the direct sunlight. When not flowering, they do best if given only medium light, as at a sunless window, although a brightly lit position in a cool room is also suitable.

Temperature: Keep these plants in as cool position as possible, preferably 7-16°C (45-61°F). If the Rhododendron simsii are brought into warm rooms – above 20°C (68°F) – the roots will dry quickly, flower will flop and leaves will fall. Move the plants gradually from cool into warmer positions if absolutely necessary, but flower will last longer if they are kept cool.

Watering: To make sure that indoor grown Rhododendron simsii are permanently moist at the roots (they are almost always potted in pure peat moss) water them plentifully, giving enough at each watering to keep the potting mixture thoroughly moist. They dislike lime, so use soft, lime-free water.
Stand pots on trays or saucers of damp pebbles for extra humidity. Another way to provide extra humidity for a potted Rhododendron simsii is to stand it in a larger pot of peat moss kept moist.

Feeding: Apply a lime-free liquid fertiliser once every two weeks from late spring to early autumn.

How to keep these plants for more than one season: Although it is not possible to retain these plants for any longer than one season entirely indoors, they can be kept indefinitely in the right circumstances. When flowers are faded, place the plants in the coolest possible position, water them moderately – enough to make the potting mixture moist throughout, but allowing the top centimetre (0.4 inch) or so of the potting mixture to dry out before watering again and put them outdoors on mild days. In cool or cold climates, wait until any danger of frost has passed. Stand them in the shade outside, preferably with the pots sunk into the ground – only if the soil is low in lime. Keep each such plant moist, spray with clear water on hot evenings and feed with lime free fertiliser. Then bring them indoors for another flowering season just as winter begins.
Once more, keep the potted plant cool while buds develop; hot, dry air will cause buds and possibly leaves to drop off. A cool conservatory or glasshouse at 7-13°C (45-55°F) is ideal at this stage. From the beginning of the flowering period until the flowers fade, brighter light and more warmth – though not temperatures above about 21°C (70°F) – become tolerable to the plant.

Potting and repotting: Use a lime-free combination of one part of soil-based potting mixture, two parts of peat moss and one part of coarse sand or perlite. Plants should be transplanted to pots one size larger every two or three years, after flowering but before being moved outdoors.

Propagation: Rhododendron simsii can be propagated by means of tip cuttings of new growth taken in spring. Plant a 5-8cm (2-3 inch) long cutting in an 8cm (3 inch) pot of moistened rooting mixture consisting of two parts of coarse sand or perlite and one part of peat moss. Enclose the potted cutting in a plastic bag or propagating case and keep it in a shady position. When the cutting is well rooted (in about 8-12 weeks), transplant it to an 8cm (3 inch) pot of the potting mixture recommended for mature plants. Thereafter, the plants may be treated as a mature Rhododendron simsii.

Yellow leaves is an indication of either an iron deficiency or the presence of lime in the potting medium or water.
Treatment: To counteract this, water with a sequestrene compound (a solution of iron chelates). Water the plant with soft water.

Leaf drop or shriveling is most often caused by dry soil. Other common causes are too-low humidity, too-high temperatures and too much sun exposure. If the plant has lost more than one-third of its leaves, discard it because it will never recover.
Treatment: Submerge the pot in room-temperature soft water, until the potting medium is thoroughly saturated (bubbles disappear), every day for a week and never allow it to dry out again.

Brown leaves can be an indication of root rot caused by soil-borne fungi. Infected plants should be discarded.

Spider mites are the most common pests and infestations occur when the air is too warm and/or too dry. Parched or crinkled leaf tips, with webbing on leaf undersides, is a sign of spider mites.
Treatment: Prune infested stems, but if more than one-third of the plant is infested, discard the plant.

Re-blooming: Unless the winters are short and mild, Rhododendron simsii plants are difficult to get to rebloom (unlike the hardy garden Rhododendrons/azaleas). Enjoy Rhododendron simsii plants as long as their flower bouquets last.

Notes: The genus name ‘Rhododendron’ is derived from the Greek ‘rhodon’ meaning rose and ‘dendron’ which means tree, so ‘Rhododendron’ is the Roses Tree.

Rhododendron is a member of the Ericaceae (heath plant) family. Relatives include Erica (heath plant), Calluna (heather), Gaultheria (salal, lemonleaf, wintergreen) and Vaccinium (huckleberry, blueberry, cranberry).

Uses: This beautiful flowering shrub is able to combat formaldehyde from sources such as plywood or foam insulation. Because Rhododendron simsii does best in cool areas around (60 to 65 degrees), it is a good option for improving indoor air in basement if can be provided with a bright spot.


Foliage – green
Features – flowers
Shape – bushy
Height: 45-60cm (18-24 inch)

Watering in rest period – moderately
Watering in active growth period – plentifully
Light – bright
Temperature in rest period – min 7°C max 18°C (45-64°F)
Temperature in active growth period – min 7°C max 18°C (45-64°F)
Humidity – high

Hardiness zone: 8b-11


Rhododendron simsiiRhododendron simsiiRhododendron simsii

Annuals, Flowering Plants, Indoor Plants, Shrubs , , , , , , , , , ,

Azalea indica ‘Inga’

Synonyms: Rhododendron indicum
Family: Ericaceae

Common name: Azalea Shrub, Azalea indica, Azalea Inga

Origin: Southern Indica azaleas (Azalea indica) are actually native to Japan and first introduced into Holland in 1680 but failed to catch on there. It reached America in the 18th century and became popular outdoor landscape plants in the warmer parts of the South. Fruitland Nurseries of Georgia was among the first to offer the emerging varieties for sale and extensive breeding both here and in Holland has produced a wide range of forms.
The name Azalea indica arose from the fact that people thought the flower was of Indian origin.

Azalea indica 'Inga'

Azalea indica ‘Inga’

Description: Azalea indica ‘Inga’ is a wonderful shrub for planting in under light, shade trees where the many flowering pink and white add a seasonal splash of colour. Ideal pot plant for shaded balconies. Evergreen compact shrub about 60-90cm (23-35 inch) tall that thrives in acidic soils. Flowers in spring and spot flowers summer/autumn. The semi-double flowers are ruffled pink with white edge.

Proper Care:
  Azaleas prefer cool, partially shaded sites, such as the filtered shade of pine trees. Azaleas planted beneath hardwoods with shallower roots must compete with these trees for nutrients and water. If placed in the right location, however, they can do well on these sites. Although some varieties tolerate sun better than others, they all prefer an area that is not exposed to long periods of hot full sun and drying winds This causes the leaves and flowers to fall off azaleas. Flowers last longer when plants are partially shaded. Azaleas exposed to full sun are more susceptible to lace bugs. Early morning sun exposure after a hard freeze may cause cold injury. Do not plant azaleas in heavy shade as poor flowering and weak growth result. Cold can blackened or severely discolored foliage.

Soil: Azaleas are shallow-rooted plants that are easily damaged by excessive soil moisture. They grow best in acid (4.5 to 6.0 pH), well-drained, organic soils. Before planting, have the soil tested and adjust the pH according to soil test results.
Azaleas located in poorly drained sites do not receive the oxygen required for healthy growth and often develop root rot diseases. When planting in poorly drained areas, add composted pine bark to as large an area as possible, and plant the root ball higher.

Mulching: A 5-7cm (2- to 3-inch) layer of organic mulch is very important. It conserves soil moisture especially through the hot summer months, maintains soil temperature and helps discourage weeds. There are many materials suitable for mulching: pine straw, composted pine bark and leaves work very well, enriching the soil with organic matter as they decompose. Keep the mulch 5cm (2 inch) away from the main stem to keep the bark dry and extend it beyond the outermost branches.

 Watering: Azalea indica ‘Inga’ are shallow-rooted plants and require irrigation during dry periods. This is especially true of those planted in the spring. Azaleas planted in warm weather in sandy soils may require watering of the root mass twice a week during the first year.
To determine when to water, pull back a small area of mulch near the base of the plant and check the moisture level of the root ball and surrounding soil. If the top few inches of soil feels dry, wet the soil deeply, to at least a depth of 6 to 8 inches.
Use soaker hoses or drip irrigation to slowly water the base of the plants. Overhead irrigation may promote disease.
Azaleas in waterlogged soils will decline and are susceptible to root rot diseases. It is important to reach a balance of regular, deep watering and good drainage to promote a healthy plant. Too wet, hot or too dry can cause the leaves and flowers to fall off azaleas

Fertilising: Azaleas have low nutritional requirements compared to other shrubs. A soil amended with organic matter prior to planting followed by a mulch of compost, shredded leaves, pine straw or other organic material will usually provide sufficient nutrients for adequate growth.
Before fertilizing, have a specific reason for doing so, such as increasing growth rate or correcting a nutrient deficiency. A nutrient deficiency can be exhibited by a number of symptoms including stunted growth, smaller than normal leaves, light green to yellowish leaf color and early leaf drop. Be aware that these same symptoms can be caused by other problems such as heavily compacted soil; stresses from insects, disease organisms and weeds; and excessively wet or dry soil. Fertilization will not correct those problems, so find out the cause of the symptoms and treat them appropriately.
The best time to apply fertilizer is when it will be readily absorbed by the roots of the plant and when the soil is moist, which can be any time from late spring (after new growth emerges) up to early fall. Avoid fertilizing plants stressed by drought during the summer months. Without water, plants are unable to absorb nutrients, so it is best not to fertilize if water is unavailable.

Pruning: There are two pruning techniques used for azaleas: thinning and heading. Thinning refers to the removal of branches back to the main trunk or another branch. This method is used to remove leggy branches that extend beyond the canopy of the plant, remove damaged or diseased wood, or reduce the size of the plant. Thinning allows light to penetrate the shrub, encouraging growth on interior branches. Thin the plants at any time of the year without causing significant impact on flowering, growth or cold hardiness of the plant. How-ever, to reduce the impact on flowers the following year, prune just after flowering in the spring.
Heading refers to the cutting back of a branch, not necessarily to a side branch. This method is used to reduce the size of a plant, create a hedge or to renew old overgrown plants. Renew overgrown plants by cutting them back to within 15-30cm (6 to 12 inch) of ground level. This practice results in abundant new growth by midsummer.
The best time to renew azaleas is before spring growth begins. This allows sufficient time for next year’s flower buds to form in midsummer, and for new growth to mature and harden off for winter.

Propagation: Azalea indica ‘Inga’ is usually propagated by 7-10cm (3–4-inch) cuttings taken after the spring growth has hardened or matured. They are also easy to root using different layering techniques.

Uses: Exceptional early spring color for beds, borders and foundation planting. Add to perimeter plantings. A natural large tree groves and the verges of wildlands or naturalistic landscapes. A traditional choice for Asian inspired gardens. Bold color for reflecting pools and water gardens.
Companion Plants:
Group this vivid azalea with other acid loving plants such as Normandy Rhododendron, (Rhododendron x ‘Normandy’), Seiryu Japanese Maple, (Acer palmatum ‘Seiryu’), Orangee Flame Oregon Grape Holly, (Mahonia aquifolium ‘Orangee Flame’) and Makinoi’s Holly Fern, (Polystichum makinoi).
Azalea indica ‘Inga’ is also suited for hanging baskets.

Azaleas have a particularly good effect on ammonia found in floor cleaning products, so these  plants are very valuable when grown indoors.


Lace bug damage on azalea leaves

Lace bug damage on azalea leaves

Lace bugs, spider mites, leafminers  / leafrollers, and azalea caterpillars are the most common pest problems for azaleas. Lace bugs are sucking insects that feed on the undersides of leaves. The top surface of the injured leaf appears speckled or mottled, and tiny black spots of insect excrement can be seen on the leaf undersides.
Treatment: Mid-spring is a great time to control these infestations. Insecticidal soap, horticultural oil, neem oil and most synthetic insecticides will kill the insects. The key to good control, though, is thorough coverage. Use a garden sprayer and pump it up vigorously. When spraying, point the spray wand up from beneath so the undersides of the leaves are covered with spray.
Another pesticide option is to use a systemic insecticide that poisons the sap of the azalea. Imidacloprid (Bayer Tree and Shrub Insecticide) can be poured around the roots of azaleas in spring, when growth begins, to achieve season-long control.

Azalea leaf and flower gall

Azalea leaf and flower gall

The most common diseases reported on azaleas include petal blight, leaf and flower gall, and various azalea declines. Petal blight is most severe during cool, wet spring weather. Infection first appears as small, white spots on colored petals or rust-colored spots on white-flowered varieties. Spots enlarge rapidly into irregular blotches, causing the blossoms to “melt” into a slimy mass. Affected blossoms dry and either drop or remain on the plant. The fungus survives on dried blossoms on or in the soil.
Prevention and treatment: Removing mulch and dead flowers 3–4 weeks before bloom reduces disease incidence. Avoid overhead watering. Apply all chemicals according to directions on the label.


  • Climate: Humid oceanic
  • Minimal temperature: 4-6°C (39-42°F)
  • Optimal temperature: 20-22°C (68-71°F)
  • Light: bright, am or pm sunlight, mid-shade
  • Soil: humus-peat-sandy
  • Hardiness Zones 8a–9b

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