Rhododendron - Rhododendron

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General information

Rhododendron belongs to the ericaceae family and is native to Asia, Oceania, North America and Europe. The name was used for this genus by Linnaeus

The rhododendron genus includes about five hundred species of evergreen and deciduous shrubs and trees. Rhododendrons are shrubs and trees that can reach a maximum height of twenty meters with persistent leaves with the entire margin. They form at the apex of the shoots. Flowering is the element that is really appreciated for its decorative properties. It begins during the spring and ends in the summer.

The flowers of the rhododendron they can be of various types. There are, in fact, the apical and axillary flowers and can be isolated or grouped in inflorescences. The flowers of rhododendrons are usually particularly large. Their shape can be bell-shaped, funnel-shaped, tubular or flattened. The same can be said for colors which can be white, pink, yellow, orange, lavender, purple, cream, purple or scarlet.

The species

Rhododendron augustinii is a species native to China. This rhododendron is an upright shrub species. It grows up to four months in height. The leaves are persistent and pointed with a dark green and scaly underside. The shrub blooms towards the end of spring and more precisely towards May. The flowers are funnel-shaped and reach a maximum width of six centimeters. The color of this color is a dark mauve blue. The throat has green spots and appear in groups of five in inflorecences.

Rhododendron auriculatum is also native to China, it is a small shrub or tree reaching a maximum height of eight meters. The leaves are oblong and persistent. Flowering occurs in summer. The flowers are very fragrant in the shape of a funnel of white color and sometimes there are pink shades. Only the adult plants come to bloom and are gathered in umbrella inflorescences with a maximum of fifteen flowers.

The Rhododendron bullatum are native to China. This is a shrubby and very delicate species, in fact it is only recommended for areas with a mild climate. It reaches a maximum height of two and a half meters and takes on a disordered shape. The leaves are persistent, take on a very dark green color with the upper part crinkled and the lower one with a bronze-colored hair. The flowers are very fragrant, white tending to cream with, sporadically have pink shades. They take on a funnel shape with a maximum length of eight centimeters and a width of twelve. They are gathered in inflorescences of up to four flowers. Flowering is very long. It begins in April and ends in June.

The Rhododendron bureavii is native to China is a shrub species and grows up to a maximum of two meters in height. The leaves are persistent and very hardy, the underside is red and tormenting, and the top is dark green.

The flowers are funnel-shaped with a maximum width of three centimeters and a length of five minutes. They are red with pink spots grouped in inflorescences composed of up to fifteen flowers.

Flowering occurs during the month of April.

Rhododendron imperator is a shrub native to Burma. It grows with an expanded habit reaching thirty centimeters in height and sixty in diameter.

The leaves are persistent with an elliptical or lanceolate shape, they are scaly with a blue-gray underside. Flowering occurs around May. The flowers are funnel-shaped with a length of three centimeters and a width of four centimeters. They are mauve pink in color, they can be isolated or joined in pairs.

Exposure and climate

Rhododenron is not particularly fond of direct sunlight. It is advisable to place it in the shade or in a semi-shady position.

As far as the climate is concerned, it must be said that there is no rule that applies to everyone. There are some species that love temperate climates and can only tolerate a couple of degrees below zero. There are other species, however, which absolutely cannot withstand the heat and mild climates. In this case, winter temperatures should never rise above fifteen degrees.

The watering

Watering must be very frequent during spring and summer and then become less frequent during autumn and winter. Since the rhododendron loves humid climates it will be necessary to spray non-calcareous water directly on the plant every day.

Soil and fertilization

The soil must be acidic and loose. If the soil is too calcareous it will be necessary to correct it with peat. In the pot it will be necessary to add pine needles and coniferous sprigs to the earth.

Fertilization must be done in early spring with slow release fertilizer.

Diseases and parasites

The pitfalls are carried out by the oziorrinco and by the red spiders.

If semi-circle erosions have appeared on the leaves of the rhododendron on the edge of the leaf the rhododendron it is infested with the oziorrinco a beetle that acts mainly at night. It is necessary to act very quickly with a specific insectivide.

The spider mite is a mite that lives very well in hot and very dry environments. Their presence is manifested by cobwebs in the lower part of the leaf. The plant and the environment must always be kept moist. Furthermore, acaricides must be used.

Varieties of the Rhododendron

The rhododendron has different varieties. Among the most appreciated by lovers of the floral world we can report in particular three.

Rhododendron hirsutum, a variety whose flowers are characterized by an intense pink color, finds its ideal habitat in the Asian mountains and the central-eastern Alps. It is a not too tall variety, in fact it does not exceed 50-80 cm and has a dense network of branches especially in the lower part.

Rhododendron ferrugineum, on the other hand, is known as Alpine rose, and is the best known species of the Rhododendron family. One of the peculiar characteristics of this plant are the flowers, with particularly large dimensions and the so-called bell shape, while as regards the color it is a fuchsia tending to red which gives this type of plant a peculiar liveliness.

Last but not least, Rhododendron chrysanthum is known in Asian areas where it grows spontaneously and where it is used in homeopathy thanks to its hypotensive and antirheumatic properties.

Rhododendron bonsai

The plants of the rhododendron genus are beautiful species capable of giving incredible blooms. In addition to the acid soil, the cool climate and frequent irrigation, they do not have great needs and are also suitable for cultivation in pots. For this reason these plants are also used to produce beautiful bonsai. In particular, azaleas are widely used but also ornamental rhododendrons are widely used. Rhododendron indicum, for example, is widely used in bonsai cultivation.

This bonsai rhododendron, which in winter must be protected from frost in case of cold temperatures, grows well with a minimum of care and attention. First of all, watering is essential and must be accentuated in the summer. Pruning is another important intervention in the cultivation of rhododendron bonsai and must be carried out after flowering both to eliminate the dry branch parts and to give a shape to the plant.

Another important intervention is the fertilization which must be carried out initially when spring begins and must be repeated in small quantities during the most intense months of vegetative activity.

The rhododendron: How to prune the rhododendron

Speaking of rhododendron, we could not help but also discuss pruning. The pruning of the rhododendron must be done very lightly trying not to cut more than necessary. The best time to prune rhododendron plants is spring and any branches that have overgrown should be cut. The shape of the rhododendron is quite decomposed but with the cut it is possible to try to contain and give a regular shape to the plant.

Remember to always use clean (possibly sterilized) and well-sharpened cutting tools and to make precise and clean cuts.

We avoid winter pruning or pruning too close to the most intense cold periods because the cut branches may not have healed yet and the frost could enter the plant causing damage.

The rhododendron. What are its main features? How to grow it?

You know the rhododendron, do you really like this beautiful plant and want to grow it in your garden or in a pot but don't know how to get started?

Do not worry! Below we will explain how you can do it.

In this article we talk about the rhododendron, its characteristics, what are its needs and the ideal environmental conditions to cultivate it in the best possible way, what pruning operations it needs and finally, what are the pathogens and diseases it can encounter.

Rhododendron cutting

Rhododendron cuttings are used to grow new rhododendron plants. If the cuttings are not taken correctly, however, no new growth will result. Taking rhododendron cuttings is a delicate procedure that must be done properly to avoid damaging the existing plant and to promote healthy growth for the new one. Once the technique has been mastered, it can be used to create new rhododendron plants almost anywhere.


• Choose the rhododendron to duplicate. Choose a healthy plant that shows no signs of disease. Check the color of the flowers to make sure they are to your liking before taking cuttings.

• Locate the north side of the plant and look at the lower half of the rhododendron.

Find a long, slender growth of at least one leaf bud on it. Leaf buds are a bit smaller than flower buds. Growth must naturally be vertical growth.

Check the color of the rhododendron shoot, which should be a pale green.

• Bend the rhododendron shoot at a 90 degree angle to check its moisture content. The shoot should fold with ease to become a suitable cut. If you shoot break, find another one.

• Trim the growth at the base with Garden Clippers.

Rhododendron planting & care

The University of Missouri Extension Service calls rhododendron an "all-weather shrub." These shrubs, with their deep green, glossy foliage, add a nice splash of color to a spring garden with their abundant flowers. The term rhododendron refers to both rhododendrons and azaleas and, once planted, they are easy to maintain as a solitary central plant or cluster along the edge of the garden.

What is a Rhododendron?

A rhododendron is a flowering evergreen shrub. Some varieties of rhododendrons can reach 80 feet, although most varieties grow to 5-12 feet. It blooms in spring with large clusters of flowers in red, lavender, purple, white, and pink. Throughout the year, its leaves have a leathery and attractive dark green color. Some varieties of azaleas are deciduous, adding even more fall color to the garden before winter in.

Selecting a location

Rhododendrons grow best in humid climates with acidic soils. Soil with a pH between 5 and 5.5 is best. They don't do well in direct sun. Choose a location with either early morning sun or filtered sun throughout the day. Do not place rhododendrons in the shade or areas of strong winds. Choosing a rhododendron that reaches a maximum size for the area is to be placed. If you want a shrub that grows to around 5 feet, choose a variety near that size that requires only light pruning, rather than a wider variety that will need heavier pruning.

Planting rhododendrons

Planting rhododendrons is done in the spring or fall. Dig a hole in well-drained soil that is wider but only as deep as the rhododendron sod. Rhododendrons have beautiful, shallow roots that don't grow quickly, so try to keep as much of the root ball as possible when planting. Once planted, trim the foliage to promote root growth. After implantation, the American Society recommends Rhododendron watering at least weekly for the first year. Insert a tube at the base of the plant and let the water drip for several hours. Keep the plant heavily chopped to retain moisture and reduce extreme temperatures. Gardner's network suggests a mulch of pine needles, as they are acidic and make the soil more acidic, which is beneficial for rhododendron.

Pruning Rhododendrons

Rhododendrons should be pruned as soon as possible after the flowering time. Rhododendrons bloom form on the tips of the stems, so pruning too late will reduce the number of flowers the following year. Prune the flower clusters after flowering and cut off the long branches to keep a compact shape. If diseased or dead branches are found, they can be removed at any time of the year.

Rhododendron Propagation

Some rhododendrons are propagated by seeds, but most of the propagation occurs by cuttings. Resinous cuttings can be taken in August or September. Take a cut that is 3 or 4 inches, and remove the lower leaves. Place the cuttings in a moist mixture of sand and peat until roots form. Then put the rhododendron cuttings in jars, and well water.

Pruning Rhododendron Guide

Although there is often little need for pruning rhododendrons, especially in naturalized settings, these shrubs respond well to the occasional trimming. In fact, excessive growth may require a heavy pruning. Trimming rhododendrons is typically done for maintenance, shaping, and rejuvenation– as is the case for overgrown plants.

The most common type of pruning is maintenance pruning, which simply involves the removal of spent flowers and old, dead wood. It is important to remove the flower stems from the shrub once blooming has ceased. Allowing these dead flower clusters to remain can actually reduce the following year's flowering. Cut near the base of the old flower cluster. Also, remove dead or diseased parts of the shrub, following the branch back to healthy wood and making your cut at that point.

Rhododendrons and azaleas, both from the genus Rhododendron, have long been mainstays of late spring because of their spectacular clusters of showy blooms — plus, large green leaves that often stay green through winter.

About Rhododendrons & Azaleas

The flowers are tubular-, funnel-, or bell-shaped — and often fragrant. The leaves of the smaller azalea are usually pointed and narrow the leaves of the rhododendron are generally large and leathery.

These shrubs prefer climates with adequate rainfall and moist summers. The two main azalea groups, evergreen and deciduous (varieties that drop their leaves in the fall) can be found in nearly every part of North America, from the frosty Canadian plains to tropical Florida. The rhododendron types are fussier, preferring environments where it is neither too hot nor too cold (Zones 5 to 8). They need a certain amount of chilling to develop strong flower buds.

With thousands of varieties, there are rhododendrons and azaleas for just about every landscape situation. There are low-growing ground cover azaleas, plants that grow from 1 to 2 feet, as well as plants that can grow up to 25 feet tall. They come in many flower colors, including pink, red, white, yellow, and purple. Though most plants flower in the spring, there are also summer-blooming varieties that add color and charm to the garden.


Buying Plants

  • When shopping for rhododendron or azaleas, pay attention to when they flower. Early varieties can blossom in March, late ones into July or even the fall.
  • Buy plants that are a deep green (not yellowed), not wilted, and well watered. Check the soil in the container with your finger and avoid plants that are bone dry.
  • If your weather heats to above 90 ° F in spring, avoid white-flowered azaleas. Their thin petals shatter in the heat.
  • In hot climates, buy plants in 3-gallon pots rather than 1-gallon pots. Small plants, with their fewer roots, struggle in the hot late spring and summer.

Choosing and Preparing a Planting Site

  • Most large-leafed varieties require dappled shade avoid deep shade or full sun. A sunny spot that receives a few hours of shade is perfect. See regional guidelines below.
  • Soil should be well-drained, humus-rich, moist, and acidic (pH 4.5–6).
  • Amend planting areas with compost, peat moss, or a substitute, only if your soil is poor. Learn more about soil amendments and preparing soil for planting.
  • Azaleas and rhododendrons have shallow root systems and need moist soil and mulch to keep them from drying out.

Planting in Cold or Temperate Regions (Zones 3 to 6)

  • Plant in full sun to increase flowers and avoid mildew problems. Shrubs need a minimum of 6 hours of full sun daily.
  • Plant on the sheltered side of a windbreak. If subjected to cold, dry winds, their leaves and buds dry out and die.

Planting in Warm or Hot Regions (Zones 7 to 11)

  • Plant in a site that receives afternoon shade, especially in hot areas. In tropical zones, azaleas will bloom in full shade.

How to Plant Rhododendron & Azaleas

  • Plant in spring or early fall.
  • Space plants 2 to 6 feet apart, depending on their estimated mature size. Dig a hole as deep as the root ball and 2 times as wide.
  • Set new plants so that their top roots are at soil level or slightly below. If you plant them any deeper, the roots may rot.
  • Fill the hole half full with soil, then water it well to settle the soil before filling with remainder of soil.

How to Care for Rhododendron & Azaleas

  • Mulch plants every spring with 2 to 5 inches of pine bark chips or pine needles to protect shallow roots and retain soil moisture. A lack of water reduces flower-bud formation.
    • Tip: A common mistake is to create a so-called “mulch volcano,” where mulch is piled heavily around the trunk of the shrub. In fact, this can keep the trunk too wet and encourage rot. Always leave a few inches around the trunk free of mulch.
  • Fertilize azaleas and rhododendrons sparingly and only when flower buds swell in the early spring, even if they are fall bloomers. Heavy applications of fertilizer will burn the plants.
  • Water plants during the summer if rainfall is less than 1 inch per week.
  • After flowering, deadhead where practical, to promote vegetative growth rather than seed production. Remove dead flowers from rhododendrons carefully next year's buds are just under the old heads and will start to develop shortly after flowering.
  • In regions with severe winters, wrap evergreen rhododendrons with burlap in the fall and apply extra mulch around the base of the shrub.
  • Azaleas and rhododendrons may be transplanted at any time during the growing season, but they transplant most successfully during fall or early spring, when they are dormant and temperatures are cool.

Pruning Rhododendron & Azaleas

  • In general, do not prune spring-flowering shrubs such as azaleas and rhododendrons. If you need to reduce height, prune after flowering in the spring.
  • Otherwise, just remove dead, damaged, or diseased branches at any time of year.
  • On young and old plants, simply snap off spent flower stalks by bending them over until they break away from their stems. Be careful not to damage growth buds at the base of each flower stalk.

Pests / Diseases

  • Vine weevil
  • Whiteflies
  • Leafhoppers
  • Lacebugs
  • Stairs insects
  • Caterpillars
  • Aphids
  • Powdery mildew
  • Bud blast
  • Rust
  • Leafy gall
  • Petal blight
  • If soil is not sufficiently acidic, root rot and lime-induced chlorosis could occur.

Recommended Varieties

There are more than 900 species in the Rhododendron genus, which vary greatly. It would take a whole book to understand this wide world!

You may be interested in joining the American Rhododendron Society, which runs a database with information on more than 2,000 rhododendrons and azaleas. On an annual basis, the society selects a number of rhododendrons to be awarded the Rhododendron of the Year designation, highlighting the best-performing plants for different regions.

Here is a handful of varieties that we think you’ll enjoy:

  • 'Blue Diamond' is a dwarf evergreen rhododendron that grows to 5 feet. It blooms mid-season with violet-blue flowers. Zones 7 to 9.
  • 'Cecile' is a vigorous azalea that grows to 7 feet and produces dark salmon-pink buds in mid-season. Zones 5 to 8.
  • 'Hydon Dawn' is a low-growing rhododendron that actually tolerates full sun. Pale pink flowers bloom in mid-season. Zones 7 to 9.
  • 'Nova Zembla' is an evergreen rhododendron that grows 5 to 10 feet tall and bears bright red flowers in late mid-season. Zones 5 to 8.
  • 'Rosy Lights' is an azalea that offers extra cold hardiness. It grows to 4 feet and bears deep purple-pink flowers. Zones 3 to 8.
  • 'Purple Gem' is a dwarf rhododendron which grows to 2 feet and is an early season bloomer. It bears small, light purple flowers. Excellent in the front of a border or in a rock garden. Zones 5 to 8.

Wit & Wisdom

The glittering leaves of the rhododendrons
Balance and vibrate in the cool air
While in the sky above them
White clouds chase each other
–John Gould Fletcher

If you are considering pruning, you should probably plan to fertilize your shrub in late fall the year before. Doing so afterward may result in leggy growth. Since buds form on next year's flowers, by the time blooming has stopped, they are already well advanced. Therefore, as the flowers fade, trim no more than 15 to 20 inches (38-51 cm.) Off the strongest branches. Cut back the plant to expose the inner branches. Follow the branch down to the last whorl of leaves you want to keep and cut just above those leaves, about 1/4 inch (6 mm.) Above the topmost leaf in this cluster.

Large, overgrown rhododendrons can be cut 12 to 15 inches (31-38 cm.) From the ground when necessary. Rhododendrons often have three or more main branches rising from the crown of the plant. Each of these primary branches should be cut at a different height to produce a more natural-looking shrub. Cut about 1/2 to 3/4 of an inch (1-2 cm.) Just above a latent bud. Pruning above a cluster of two or three buds is even better.

Sometimes more severe pruning may be necessary, requiring cutting to about 6 inches (15 cm.) Or so from the ground. Their adventitious buds at the base of the plant will send up new shoots, but keep in mind that flowering usually will not occur for up to two or three years after this heavy pruning.

Video: How to Transplant a Rhododendron. This Old House

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