Rhododendrons

A tree that the wasps love...

Credit: Elen DelSignore
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Botanical name: Rhododendron

Plant type: Shrub

USDA Hardiness Zones: 4, 5, 6, 7, 8, 9

Sun exposure: Part Sun

Soil pH: Acidic


Flower color: Red, Pink, Yellow, Purple, White

Bloom time: Spring, Summer

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

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

This shrub generally performs best if they are provided with moisture and shelter under trees.  They prefer climates with adequate rainfall and moist summers. The two main azalea groups, evergreen and deciduous (varieties that drop their leave in the fall) can be found in nearly ever 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 as well as plants that can grow up to 25 feet tall. Though most plants flower in the spring, there are also summer-blooming varieties that add color and charm to the garden.

Planting

  • Most large-leaved varieties require dappled shade; avoid deep shade or full sun. A sunny spot that receives a few hours of shade is perfect.
  • Soil should be well-drained, humus-rich, moist, and acidic (pH 4.5–6).
  • Amend planting areas with compost, peat moss, or a substitute, and oak leaves to achieve ideal conditions.
  • Azaleas and rhododendrons have shallow root systems and need moist soil and mulch to keep them from drying out.
  • The best time to plant is in late spring or early fall.
  • When shopping for plants, 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.
  • 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.

Care

  • Mulch plants annually with 2 to 5 inches of pine bark chips or pine needles to protect shallow roots, retain soil moisture, and keep the soil damp. A lack of water reduces flower-bud formation. (Keep mulch a few inches away from the trunk.)
  • 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.
  • In regions with severe winters, wrap evergreen rhododendrons with burlap in the fall.
  • Transplant azaleas and rhododendrons whenever the ground is not frozen or waterlogged.

Warm-Weather Advisory (Zones 7 to 11)

  • If your weather heats to above 90°F in spring, avoid white-flowered azaleas. Their thin petals shatter in the heat.
  • Plant in a site that receives afternoon shade, especially in hot areas. In tropical zones, azaleas will bloom in full shade.
  • Buy plants in 3-gallon cans rather than 1-gallon cans. They're a better bargain in hot climates. Small plants, with their fewer roots, struggle in the hot late spring and summer.

Cold-Zone Reminders (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.
  • Plan on the lee side of a windbreak. If subjected to cold, dry winds, their leaves and buds dry out and die.

Pruning

  • Do not prune spring-flowering shrubs such as azaleas and rhododendrons.
  • 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

  • Susceptible to vine weevil, whiteflies, leafhoppers, lacebugs, scale 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 of rhododendrons which vary greatly. It may take a book to understand this wide world. You may also be interested in joining the American Rhododendron society which runs a database with information on more than 1,200 plants.  Find out more at www.rhododendron.org.

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

  •  'Blue Diamond' is a dwarf evergreen shrub 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 deep red flowers in late midseason. 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.

Special Features

  • Attracts Birds

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

Free E-Card

Send this e-card of a colorful rhododendron!  Or, browse more flower photos in our e-card gallery!

Comments

hi honored i want to know if

By Getoar on July 17

hi honored i want to know if this tree gorw up in europe , and if this is good or bad for the honey bees

How far from the side of the

By Robert BishopAvKah

How far from the side of the house should I plant rhododendrons? Can I plant now or should I wait until fall?

Hi, Robert, If you are in a

By Almanac Staff

Hi, Robert,
If you are in a moderate climate, you can plant almost any time. In a cold climate, the ideal time to plant is early spring; early fall is second choice. (You want to give the plant time to adapt.) In a hot climate, plant in fall (so that the plant has time to adapt in the cooler portion of the year).
Rhododendrons are common in foundation (near the house) plantings. Take into consideration how tall and wide it will get (or how tall you want it to get; note that controlling its size will require pruning). You can learn more about this on the plant tag, possibly from the vendor who sold it, or be doing a bit of research on the particular variety you have.
We hope this helps!

We planted 4-5 variety of

By Kay Meade

We planted 4-5 variety of kinds of Rhododendrons this past fall. It was a hard winter in KY and now all of them seem to not be doing well. They look sick and not growing or producing new growth. One kind has a film covering the leaves - looks a little like aphids do but when I wipe the leaves off there is only a film but no apparent bugs. Another kind is shedding lots of leaves. We are not sure what to do but can't seem to find any helpful information. Please help

Hi, Kay, Some

By Almanac Staff

Hi, Kay, Some deteriation—leaf drop or droop—is not uncommon after a hard winter. Keep them well watered in well draining organic soil, and layer on some rich, organic mulch.
The film may be powdery mildew. It is grayish white and powdery; you have not menitoned a color. Iif it is powdery mildew, it could be caused by high humidity.
It also could be a local insect. You will do best by consulting a local nurseryman or cooperative extension service or a master gardener; the latter can often be foudn through a garden club.
Sorry we can't be more specific.

Hello my name is Roger, and I

By Roger Mater

Hello my name is Roger, and I viewed your advice on rhods and azaleas. I really liked the advice that you gave, I have an azalea that lost all of it's leaves over the winter and only 6-8 grew back this spring, and now those are dropping off. It looks like it is dying or dead. can it be save or is it a lost cause. It is, or was a beautiful bush. It is about one and a half -two foot tall and when it blooms it is absolutely gorgeous. What advice would you be able to give? Thank You!

Hi, Roger! Thanks for your

By Almanac Staff

Hi, Roger! Thanks for your comment. Hope we can help... A initial consideration for almost any failure to thrive is soil quality and pH. Rhododendrons and azaleas prefer acidic soil. That's another way of describing the pH, and pH can be checked with an inexpensive soil tester. A good nurseryman/woman or your local extensive service can help you with that, too.
Rhodos and azaleas also like organic material in the soil and organic mulches on top. As noted below, give the plants a good dose of aged manure in late fall (or not al all). Fertilizer specifically designated as for azaleas is also recommended, but only in later winter or early spring.
Also, keep the water coming, especially in warm, dry periods.
We wish you the best!

I just bought a rhododendron

By Honeyplum

I just bought a rhododendron a week and a half ago and planted it in a sunny area as it says part sun/part shade but they were at the garden center outside in a sunny area so I thought it would be ok. I planted it in my far back corner in my backyard where we used to have pine and spruce trees but had cut them all down. I was wondering if the roots from the tree would kill it? I've watered it everyday if it hasn't rained and its only had one feed of fertilizer when I planted it. Just not sure what I am doing wrong that its dying?

It's not likely the the tree

By Almanac Staff

It's not likely the the tree roots killed it. Every plant has a period of adjustment to its new home/location. You do not describe what "dying" looks like but some foliage droop is normal in dry, warm afternoons. If the leaves are drooping in early morning, it needs water.
Watering it is good; keep doing that. Also mulch it with organic material—leaves, pine needles, wood chips or the like—to maintain moisture and eliminate the need or desire to cultivate the ground.
Spread aged manure under the plant in fall—or not at all. IN other words, do not do this at any other time.
Finally, if you continue to have problems (or after reading this), contact the source, the place from which you bought it, and ask if they advise any particular care.
Hope this helps!

We have what we believe is an

By Wendy ver

We have what we believe is an Azalea which has bright orange blossoms. Which type would this be? We want to plant a matching one at the other end of the yard. Can we cut from this one and start another one? How would we do that?

You can take a cutting from

By Almanac Staff

You can take a cutting from your azalea and plant it. You will know it is the right time to do this when a shoot that comes from the end of existing wood (not the strong thick shoots that come from the base of the plant) is between soft and brittle. It should not bend like rubber, nor snap like a twig. Cut it so that it is two to five inches long, remove all but the top few leaves. Scrape off an inch or two of the bark at the planting sight, then use a rooting hormone. When planting, use a 50/50 peat and perlite mixture. Water regularly.

Wondering how I plant a Rhod

By Lisa Balestracci

Wondering how I plant a Rhod so that it grows as a shrub and not tree like. I've heard it is how you cover the root system,is this true? Thank you!

Hi Lisa, Pruning back young

By Almanac Staff

Hi Lisa,
Pruning back young plants will help to promote bushy growth. Shaping is best done in late winter or early spring, while the plant is dormant. This type of pruning will also remove some of the newly flower buds and you will have less flowers in the spring.

I am wondering if

By Mouse

I am wondering if rhododendrons produce many "volunteer seedlings" like burning bushes do? I see several bushes on my way to work where nobody lives and was hoping that they maybe put out seedlings that I could easily dig and transplant in my yard. So that's the question . . . do they put out seedlings under the parent bush??

my rhodies are doing badly!

By karen from illinois

my rhodies are doing badly! ive lost one! this is their 3rd season. im going to use mulch and see if that helps but can i cut away bad leaves? my one is blooming this year but has alot of bad leaves they are 2-3 feet tall. also i have an azalea looks dead right now but should bloom it did the same last year. but should i trim that down before rebloom? its small maybe 1-2 feet,.

Hi Karen, Don't prune before

By Almanac Staff

Hi Karen,
Don't prune before blooming. Wait until the blooms fade and then cut off any leaves and branches that look dead. Adding mulch is a good idea.

I purchased 3 rhododendrons

By Shelley Camm

I purchased 3 rhododendrons for my garden about 3 years ago. My gardener planted them in the shade of a sand cherry and they have not thrived. They are still alive but have not flowered.

I live in a zone 5a/5b area, and I am wondering if it is safe to transplant them. If so when can I do it and what type of light do they prefer?

Most rhododendrons like

By Almanac Staff

Most rhododendrons like dappled shade; a sunny spot that receives a few hours of shade is perfect. Late spring and early fall ar good times to transplant the bushes.
 

I just bought Azaleas at

By Jennifer Joan Lambert

I just bought Azaleas at Walmart for Mother's Day. I am surprised to read on the write-up that they require a sunny room all day and grow 12-16 in. tall and 12-16 in. wide. Will they flourish outside in the garden like "normal" azaleas? Will they grow bigger? What kind are they? Please help.

You bought tender indoor

By Almanac Staff

You bought tender indoor winter- and spring-blooming azaleas. They are also known as florist's azaleas. These plants will not tolerate freezing temperatures and will do best as house plants and may or may not rebloom. Prune the tips of the branches after flowering and it may produce more blooms.

just planted some azaleas and

By trevor johnson

just planted some azaleas and rhododendron do they regrow each yr

Most azaleas and

By Almanac Staff

Most azaleas and rhododendrons are perennials and will give you many years of beautiful blooms.

I bought a home last early

By Carla Zvonek

I bought a home last early spring which has a beautiful Rhod in the front garden. Last spring it bloomed lovely flowers. In late fall it started buds again. I didn't prune and the plant went through a very harsh winter with buds and leaves. (I've never had a Rhod before- is this common?)
Now it's early May in Illinois and the Rhod's buds are not opening. They are not shiny green but more green/brown/dull as are the leaves. The buds and leaves do not look dead but maybe they are. Should I cut back to the ground? Thanks!

It's normal for a

By Almanac Staff

It's normal for a rhododendron to have some brown leaves and buds after a severe winter. Don't cut back to the ground. If there is still some green there is hope. If the buds are brown, they are frost damaged and can be left or removed. When removing buds, try not to damage any new growth.

My friend's twenty five year

By Sherlla Morgan

My friend's twenty five year old white azalea has one single pink bloom right in the center of the shrub.This is the first time this has happened. What could cause this to happen?

Occasionally, azaleas will

By Almanac Staff

Occasionally, azaleas will “sport” different color flowers on the same branch. The sporting may be caused by a genetic mutation but it's nothing to be concerned about.

HELP!! My rhododendron isn't

By Elise R

HELP!! My rhododendron isn't doing so well. It's been established for many years. Unfortunately, due to our harsh NY winter many leaves have died and the buds look brownish. This has never happened before. Please let me know what I can do. Thanks!!!

If the buds are brown and the

By Almanac Staff

If the buds are brown and the flowers fail to open, this is probably bud blight (a fungus). This is usually caused by early frosts or late frosts. Is your variety hard for the climate? You need to remove the brown buds (but do not compost). A fungicide usually isn't needed since it was due to frost.

The rhodoendrum we have in

By Raya

The rhodoendrum we have in our back yard is wilting and we have watered it repeatedly. What can I do to try and help it? We have several others that are doing fine just this one is having problems.

Wilting plants are sometimes

By Almanac Staff

Wilting plants are sometimes a sign of fungal root and crown rot. Is the plant set more deeply? Is it in a site that has poorer drainage than your other plants?
If you can, lift and replant the rhododendron. Plant in well-drained and well-aerated soil. Heavier clay soils should be amended with organic matter before planting. Avoid planting in areas where water can collect around plant roots. You could even hill up the soil before planting.

This past cold, long CT

By barbara phelan

This past cold, long CT winter the deer have eaten ALL the leaves from my rhodies and azaleas. What should I do? Can I cut them back?

Wait and see if the plant is

By Almanac Staff

Wait and see if the plant is starting to produce new shoots along the stems. Cut back any dead branches.

I live in Oregon and have a

By houfie

I live in Oregon and have a large number of rhodies. Most of them are doing great, with glossy leaves and profuse blooms. I have a couple, though, that look stressed. The leaves are drooping and have a brownish tinge. The buds have set, though, and look like they will bloom. I'm curious if I need to move them (both are in shade), amend the soil or fertilize. Many thanks for any advice.

If these are the only two in

By Almanac Staff

If these are the only two in the shade we would recommend moving them. If not then amending the soil may help. Add compost to the soil and see if that will help.

I am thinking of planting a

By cia van orden

I am thinking of planting a rhod. in a largish pot in a shady spot in Sunset Zone 15. Northern Ca. Guerneville. I see many around the hood but in the ground.

I have had my rhododendron

By Atha Garland

I have had my rhododendron for 2-3 years now and they are still not blooming that is the problem

It can take 2-3 years after

By Almanac Staff

It can take 2-3 years after planting for rhododendrons to bloom. There are also many other reasons for a lack of flowers and some varieties bloom less than others. Cold temps. in the spring can kill new buds. Does you rhododendron get enough sun? Add compost to the soil around the bush and you may also want to test the soil (5.5 pH is recommended for rhododendrons). See our planting and care tips on this page for some more guidence.

What kind of fertilizer do

By Joan DiSarcina

What kind of fertilizer do you recommend for rhododendrons?

Very little fertilizer is

By Almanac Staff

Very little fertilizer is necessary for rhododendrons if you have proper soil preparation with organic matter and mulchingwith compost. They have low nutritional requirements.
You do want to ensure your soil acidity. The plants thrive best at a soil pH between 5.0 and 5.5.
Do not fertilize rhododendrons at planting; newly planted shrubs can be fertilized after they become established.
Some gardeners do an application in early spring. Ask your garden center for a fertilizer especially formulated for acid-loving plants and follow directions. Fertilizers supplying the ammonium form of nitrogen are best.
A fertilizer analysis similar to 6-10-4 applied at 2 pounds per 100 square feet to the soil surface is usually adequate. Cottonseed meal is also a good fertilizer. Do not apply any fertilizer after the first week in June. 

I have moved into a house

By new to this

I have moved into a house that has azaleas in the front of the house. There are 5 plants but all are sparse and leggy, I would like to know how I can bring them back to a full beautiful state, any suggestions?

After the blooms have faded,

By Almanac Staff

After the blooms have faded, you can prune the azaleas. Prune to shape and prune back the taller shoots to where they originate. Don't prune after July or you'll remove next year's flowers.

I just planted new

By Stacy Dohlman

I just planted new rhododendrons last fall. This winter A rabbit drastically pruned one back. All the leaves are gone and it is very short. Will it survive? Or should I plan on replacing it?

We'd go ahead and cut the

By Almanac Staff

We'd go ahead and cut the rhododendruns back, water, and fertilize them with aluminum sulfate, and see if they make it. You'll know soon.

I have older plant they have

By marjorie siegman

I have older plant they have become very leggy. Can I cut them way back? If so when and how? Thank you

Normally, rhododendron need

By Almanac Staff

Normally, rhododendron need very little pruning. However, they can become leggy as the years roll by. You can prune in the early spring. Here is a great preference page from the American Rhododendron Society. Pay attention to: When to prune (early spring), How to Start, and Pruning to Rejuvenate.

I just planted a Pieris

By Beaver Den

I just planted a Pieris Japonica Variegata in a very sheltered spot near my front porch. It doesn't get any direct sun there. I live in Ottawa, Ontario where we have very cold winters. The garden center neglected to tell me how particular these plants are. Do I have to use burlap every winter on this shrub? I am tempted to return it.

Your biggest issue is lack of

By Almanac Staff

Your biggest issue is lack of direct sun.  These plants need full sun or partial sun and shade. They'll grow without direct sun but they won't flower well. Growing in a protected site is good as they need to be sheltered from winds. A site sloping
to the north or east is best. Low areas should be avoided as should areas beneath shallow-rooted trees, including maple, ash, and elm.
Very little winter protection is needed if you have the right planting site. Cut back on watering in mid-September to help plant tissues mature before winter. However, a good watering before freeze in November is a good idea. If you have tree limbs (or an old Christmas tree), it can help to lay the boughs around the plants for added protection in wintertime. The rhododendron is a great winter plant because it keeps its lovely green leaves throughout the season.

Can a rhododendron be

By John J

Can a rhododendron be transplanted by digging a portion of the plant out and moving to new location? If so when?

Yes, rhodies transplant well

By Almanac Staff

Yes, rhodies transplant well if done properly. You need to get all the roots out. In terms of timing: Early spring transplanting is recommended for cooler climates.  Very late summer to late fall transplanting is preferred in warmer climates. Really, the only bad time is the hot periods of summer.

I have heard it is possible

By Gallatin

I have heard it is possible to start new Rhody shrubs by cutting and planting the pieces. Does this actually work? Do you need a root-growth powder to dip the ends into first?

Yes, you do need a rooting

By Almanac Staff

Yes, you do need a rooting hormone. The powder kind is most common. Here's a good reference page on how to root a hydrangea cutting: http://www.rhododendron.org/v48n4p201.htm

Rhodaderum got to big need to

By Vernon L Stallings

Rhodaderum got to big need to cut back when can I do it

In general, rhododendrons

By Almanac Staff

In general, rhododendrons don't need to be pruned, however, if they are getting too big, reduce the size with light pruning. Remove the flower clusters on rhododendrons as soon as flowering is complete. If it's just overgrown, you can actually prune it back to the stubs and it will recover in a few years and become a shapely young-looking plant. 

My azaleas (20 years old)

By KenP

My azaleas (20 years old) have never been pruned but have in the past couple of years been overrun my my neighbors ivy. The ivy is very difficult to control. And suggestions? Thanks, Ken

Do you mean English ivy? This

By Almanac Staff

Do you mean English ivy? This is a non-native plant which is an invasive that threatens other plants. Perhaps you can speak to your neighbor because it needs to be cut down before seed set and potential spread of this species. Chemical control measures for English Ivy can be
found in the Plant Conservation All
iance web site here: http://www.nps.gov/plants/alien/fact/hehe1.htm

we live in south and received

By A nonymous

we live in south and received a rhododendron for b,day should we wait until fall to plant it out it get real dry in summer. where should we keep it if we wait until fall under a shade tree or in the house thanks

In warm climates,

By Almanac Staff

In warm climates, rhododendrons are best planted in the fall. They require: excellent drainage, a soil pH between 4.5 and 6.0, and protection from hot afternoon sun so a high canopy of filtered shade is a good idea. Oaks and pines are a great companion. They must have a constant supply of moisture but never sit in stagnant water.

pruning rhodies

By Anonymous

do you mean NEVER prune? We have two large rhododendron bushes which are growing almost to roof height, one of which is also growing outward invading the driveway. i had heard that you must be careful when pruning rhodies, but would like some specific guidelines, if possible. Thanks!

You CAN cut them back but no

By Almanac Staff

You CAN cut them back but no need to routinely prune a rhododendron. According to the American Rhododendrum Society, "If a plant grows out over a walk or needs to be restricted for some reason, it may be pruned back moderately without fear that the plant as a whole will be damaged. It is often possible to do this pruning during the blooming season and have flowers for the house. Old leggy plants may need pruning, but often these are better replaced with smaller newer varieties. Old plants, however, can be cut back severely and still recover, although it may be a while before they bloom again."

Thanks

By mikeknox1952

I just wanted to drop you a line to thank you for your hospitality during my stay. I got this "rhodo" shot from the Old Farmer's Almanac site. I hope you like it.

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