How to Grow Rhododendrons

By Matt Gibson and Erin Marissa Russell

Rhododendrons are often mention in the same breath as azaleas , as they are both bloom shrubs from the Rhododendron genus . Both bush are quite popular increase to give blossom gardens due to their tension - costless tending requirements as well as their gorgeous cluster of fragrant , showy flower that seem in late springtime . Rhododendron ’s blossom come in many different wraith , include red , clean , icteric , pinkish , and purple . The colorful clusters are put by the shrub ’s orotund , drab - gullible , leathery leafage that supply a green backcloth all throughout the winter .

Hardy to USDA hardiness zones three through nine ( they develop best in zones five through eight ) , gardeners can enjoy rhododendron all year long . Though most cultivars are outflow bloomers , summertime - blooming rhododendron kind are also usable . There are literally thousands of rhododendron varieties available , some are belittled footing cover plants that spread out to meet in empty outer space in your garden beds , stretching out while continue low to the footing . Some rhododendron cultivars are average sized anthesis plants , which institutionalise up bloom haunt one to two feet tall . There are even large , tree diagram - sized rhododendron cultivars that can grow up to 25 feet magniloquent .

Rhododendrons flowering shrub

Rhododendrons enjoy areas with rafts of rainfall and moist summertime weather . rhododendron are more selective in their preferred originate environments than azaleas , requiring restrained temperature and more stability in term of climate .

When make up one’s mind which rhododendron assortment to grow in your flower garden , focus on flowering times to keep their color going in the garden all year long . Early blossom rhododendron cultivars bloom as early as March , while later bloomers heyday in July and even well into autumn . When selecting plants from the greenhouse , look for rhododendron that are deeply unripened and well - provisioned ( avoid yellowed leaves ) . Stick a finger in the soil to check the moisture level and take a pass on any plants that are sit in a bone dry substrate .

If you live in a raging climate area , buy plants in 3 - gallon pots instead of 1 - Imperial gallon flowerpot , as little flowers with less - make grow root system are more potential to sputter in warm springs and spicy summers .

purple rhododendrons with text overlay gardening tips how to grow rhododendrons

Varieties of Rhododendrons

With thousands of Rhododendron mob plants to take from , it ’s nearly impossible to get to screw the differences between the many plants in the genus . TheAmerican Rhododendron Societyannually awards 8 different cultivar with the Rhododendron of the Year ( RotY ) honor , select one Rhododendron diverseness from every region of the U.S. that is worthy of the selection .

One way to try out new rhododendrons is to allow the smart set to choose them for you by growing the regional winner of the former yr ’s award this year . So , each year , when the award winners are announce , jot down the mintage from your region and put in an order for seminal fluid from that cultivar so that you may grow the regional winners each year , one year after they are awarded . Not only will growing the smart set ’s top regional selections each year help you to become more familiar with the genus , you might find oneself yourself becoming more familiar with the region ’s growing tendencies as well .

Though there are right smart too many rhododendron species to list , there are quite a few recognise cultivars that have received high praise from flower enthusiasts . Here is a tilt of some of the most renowned varieties usable , as well as a few standouts recommended by other gardeners around the globe . set off your own list of preferred cultivar and jot down the species that really stand out . Until your Rhododendron list gets flesh out again by rhododendron varieties that you have first helping hand experience with , stay to piece out cultivars from the list below .

April Rose – A semi - dwarf shrub that reaches four feet tall at full maturity . The April Rose cultivar has unripe leaves that turn ruddy - white-livered during autumn and get two - inch - wide abstruse - purple bloom in early leaping . This cultivar is a former winner of the RotY award .

Black Satin – The Black Satin rhododendron cultivar provide a stark contrast between dark foliage and bright flower colouring material , with optic - captivate pinkish flowers rule the spring and dark purple - Shirley Temple Black folio sovereignty through the winter . .

Blue Diamond – Hardy to USDA zone seven through nine , the Blue Diamond cultivar is a dwarf variety that produce to five feet tall . Its prime browse from reddish blue to blue .

Blue Peter – This sun - tolerant variety is a intercrossed shrub that tops out at four feet tall . In mid - leap , it give rise luxuriant , showy , lavender blooms .

Boule de Neige – The Boule de Neige , or Ball of Snow in English , requires abstruse - shade , and is decorated with large , delicate , white flower in the Spring .

Bow doorbell – acquire only three to six human foot tall , but with a six foot feast , the Bow Bells bush produces pink blooms that start out deep pink and slicing to blench pink as they mature .

Calophytum – Calophytum is a large flowering tree diagram variety that can grow higher than 40 feet tall in the wilderness , but ordinarily does n’t acquire much higher than 10 feet tall when cultivated . It produces horn - shape , creamy pinkish flowers . This cold tolerant cultivar is a former achiever of the Royal Horticultural Society ’s Award for Garden Merit .

Cecile – Producing turgid , salmon - pink blooms in mid - season , the Cecile azalea kind can originate as improbable as seven groundwork in zones five through eight .

Daviesii – aboriginal to Mexico , this shrub can gain six invertebrate foot tall and wide-cut , with highly fragrant yellow bloom that turn to orange at the tips . A former RHS award winner .

Elvira – This variety thrives in nerveless - weather condition climates , hardy as low as zone 4 . It ’s showy bright - red bloom leave behind a hold up impression .

Freya – From May to June , the Freya cultivar give rise gorgeous yellowish - pink flowers . This variety is easygoing to grow , but very unmanageable to disseminate .

Gibraltar – Hardy to zones five through eight , the Gibraltar variety is known for its bright , trumpet shaped violent - orange blossom and its wide , undecided - growth use . Highly adorn , the Gibraltar is a former RHS and RotY winner .

Golden Lights – An specially cold hardy cultivar , the Golden Lights rhododendron has vivacious orange flowers and narrow , olive - green leaf .

Homebush – The glossy pink flowers of the Homebush variety help the works stand out in the natural spring . In the fall , its attractive foliage takes on the lead role . draw in a wide-eyed compass of pollinators in the spring . Hardy to zones six through eight .

Hydon Dawn – One of the only variety to tolerate full Dominicus locations , the low - growing Hydon Dawn cultivar is hardy to zones seven through nine . Forms pale pink midseason flowers

The Mighty Rhododendron – grow frilly Battle of Magenta flush that appear like pom - poms . Hardy to zones six through eight .

Nova Zembla – Hardy to geographical zone five through eight , the Nova Zembla create bright red flowers from mid to former time of year . An evergreen plant cultivar that grows to five to ten feet tall .

Rosy Lights – This cold stalwart azalea miscellany arise to four foot tall and displays purple - pink blooms in zones three through eight .

PJM Elite – A insensate hardy cultivar that grows well in zones four through eight , the PJM Elite is known for producing an abundance of red to purple heyday in mid - give .

Purple Gem – This early - flower dwarf rhododendron cultivar grow only two foot high and display little purple flowers , making it perfect for front margin .

Rubiginosum – This variety is a small tree cultivar that can grow up to 20 foot gamey . Produces trumpet - mold flowers that lay out from pale lavender to pale pink .

Saffron Queen – The wan - chickenhearted horn - determine flower of this cultivar are make love to attract bees , butterfly , and hummingbirds to the garden . This shrub can grow up to six foot marvelous .

White Angel – Growing as gamy as six feet and producing an abundance of showy long - lasting , white flowers in mid - April , the white angel variety thrives in fond tone environments .

Windbeam – This shrub ’s flowers begin out white and fade to blanch pink . The abundance of blooms that are on display on this pocket-size bush , can make this form a show - stopper in the garden . A stale hardy species , Windbeam is sturdy to zones four through eight .

Windsong – This evergreen species combines glossy - fleeceable foliage with unknown yellowish - green blossom .

Growing Conditions for Rhododendrons

Rhododendron postulate an acidulous soil with lots of organic material , a high-pitched - quality mulch , and logical moisture levels . Some varieties prefer fly-by-night locations , but most enjoy full sun . The idealistic ground pH for rhododendron is between 4.5 and 6 , which makes nutrients water - soluble , so that the roots can get at them easy . If your soil pH is above six , employ sulphur , never aluminium sulfate , to lower it . If it is too low-toned , employ ground limestone to raise it . atomic number 20 , which is on a regular basis leached out of the ground , is essential to rhododendron growth . To supersede lose calcium , sum up a tablespoon of gypsum to your plant food prior to software . Boost atomic number 20 level in your soil once per year .

How to Plant Rhododendrons

In temperate mood , such as zona three through six , rhododendron should be planted in full sun to increase blooming and to avoid publication with mildew . bush require at least six hours of full sunlight each day . Rhododendrons will brook if break to cold , dry wind conditions . high-pitched wind can damage the plant , and stale , dry climates can cause the farewell and bud to dry out out , shrivel , and pop off .

In warm locations , such as zones seven through 11 , find fault a position that gets afternoon tone to give your rhododendrons a break from the intensity of the sunshine . This is especially crucial in very hot areas . Azaleas , as well as rhododendron , are known to flower in full shadowiness in tropical climates .

establish your rhododendrons in the springiness or in early fall , spacing each plant life two to six feet aside . Adjust spacing free-base on the approximate size of the cultivar at maturity . Dig a golf hole in the soil as deep as the theme ball and twice as wide . novel plant should be set in the primer so that their top roots stay at soil level or just beneath it . If the solution ball is entomb too profoundly , the ascendant are potential to rot . After placing the ancestor ball in the muddle , back fill it halfway full with soil , then irrigate it well to facilitate the soil decide . After the first turn of grime settee into seat , fill in the rest of the dirt .

It is better to plant rhododendron in the fall . The plant will tolerate spring or winter planting , as long as it does n’t suspend , but downslope planting will harvest the dependable upshot . If you want to implant your rhododendron in the summer , you will want to supply raft of surplus piddle , especially in the start until plants are establish . Summer sow plants should be provided with a shady location that never arrive to a fault hot . Avoid found in areas that are flood prone , as these shrubs will not tolerate any standing water system .

Care for Rhododendrons

Mulch plants in the spring with a two to five inch layer of pine bark or true pine needles to shelter shallow root and improve grime moisture . Insufficient moisture will thin out blossom . pull up stakes a few inches around the trunk loose of mulch to avoid bunk issue .

trammel feeding to once a year , when flower bud begin swelling in the early spring . Heavy fecundation will cauterize your plants . supply urine in the summer when rainfall is below one inch per calendar week . Deadhead spent blooms to promote more vegetational outgrowth and confine seeded player production . Remove stagnant flowers cautiously , as the next bud sit decent below the old heads , and they will start to grow just after unfolding occurs .

In region with cold wintertime weather , protect evergreen rhododendron by twine them with gunny in fall and putting down extra mulch around the base of the industrial plant . Transplant your rhododendrons and azaleas any time you like during the develop time of year , however , precipitate or other spring transplant will have more success , when they are abeyant and the atmospheric condition is coolheaded .

leaping flowering shrubs like rhododendron and azalea do not want clip . Lower height by pruning just after bloom in the spring if needed . Other than pruning to reduce height , the only pruning necessary is to murder idle , damaged , or diseased branches anytime they are remark . Carefully break up off faded flowers by turn them until they bring out slack from their stems . Take care not to damage the growing bud that pillow at the base of each flower angry walk .

How to Propagate Rhododendrons

The fastest and easy propagation method for rhododendrons is cuttings , which can be machinate throughout the summer months . Collect six to eight inch clipping take from non - flowering stems and remove lower leaf . Keep only the topmost one or two sets of leaves . Dip the base of the cut in a powdered rootle agent ( rooting internal secretion are optional , as plant will develop roots without boost as well ) . space cutting off into pots filled with a swerve filth mixing . Keep the mix moist and put the pot near a light seed , but do not let out it to direct sunshine . beginning will get down to develop in two to three calendar week . Once roots germinate , the plants can be transplanted outdoors .

Garden Pests and Diseases of Rhododendrons

Some of the trouble a nurseryman of rhododendrons may experience is not due to insect infestation or disease but instead to excess water in the soil . If the nurseryman is watering too much , the weather condition is especially showery , or the soil where rhododendrons are grow does not ply sufficient drain , the leaf and flower buds of rhododendron plants may set out to turn brown . Rhododendrons turn in ill draining dirt that make “ sloshed groundwork ” ( water around the roots ) can also show white-livered discolouration instead of brown .

Rhododendrons become discolored like this to express their displeasure whenever the dirt around their base is oversaturated , so ensure not to overwater and to select a spot for rhododendron that drain well . you’re able to ameliorate the drain in a location by mix sand into the soil to improve its texture and loose it up . When you ’re plant a rhododendron , you could also line the bottom of the yap you dig out for the plant with either pebble or remains marble . Both these items will create diminished spaces between them that water supply can flow through when it needs to drain .

To keep your rhododendron in fine fettle , nurture the plant life with a fertilizer blend that includes heath at the conclusion of each winter season . This discussion will both aid the plant grow strong enough to avoid skin with minor disease and boost the beauty of its blooms . Once your rhododendron is established in its location , as long as the rise condition match its preferences , it should develop strong roots and naturally resist most disease or louse infestations .

On the other side of the coin , plants that do not have their care and maintenance penury met and those that call for nutrition or water are vulnerable to health problems and may struggle with one minor illness after another . To learn how to diagnose when pesterer or insect have trouble for your rhododendron and to find out what you should do if these problem rear their heads , cite the listing below .

Phytophthora root rot is especially dominant when dirt is too wet , and it is exacerbated by plastic flat coat covers and poor drain . Other peril cistron include affectionate temperatures , high levels of salinity ( common salt ) , high pH level , and damage to plant roots . This disease can strike plants growing in container as well as those planted in the ground . The pathogen behind phytophthora ascendant bunkum can subsist in the soil or in works debris for eld as oospore or chlamydospores when the weather is not pixilated enough for them . They can also jaunt on gardening tool , plant life container , in pot soil , via water system , or on infected plants .

This disease set on the theme scheme and begin stimulate it to rot and decay , then it overspread up through the tissues in the works ’s inner bark and stems . A canker sore may appear at the fundament of the stem as the stem rotting circularize up through the eternal rest of the plant life . Fibrous etymon begin to show symptom first , changing coloring material to become brown or black , and then discolouration spread through the plant ’s entire root scheme . Brown and ignominious lesions break on with child rootage , and root tissue paper that is not discolored will appear pallid , in shades of white , chicken or light green , in demarcation , and it will feel moist . As the stem sabotage , the plant will be less safe in the soil and may become rickety or well-to-do to dislodge .

After the rot has spread significantly , the industrial plant may show signal of other stresses , such as drought emphasis or malnutrition , because it is not capable to take in as much moisture and nutrients as it ask through its damage roots . Sometimes the disease is not mark until these symptoms appear above undercoat , which let in discoloration of leave to yellow or a reddish - green shade and folio curl up or wilting . This wilt will not be resolved regardless of how much H2O you provide . When the rootage rot is fatal , plants die with their foliation still seize to the branches .

gardener can avoid ever postulate to combat genus Phytophthora root molder by choosing resistant rhododendron loan-blend from the showtime . Resistant assortment let in R. davidsonianum , R. delavayi , R. glomerulatum ( R. yungningense ) , R. hyperythrum , R. keiskei , R. lapponicum , R. occidentale , R. quinquefolium , R. sanctum , R. pseudochrysanthum , R. simsii , and R. websterianum . somewhat resistant crossbreed include Anna H Hall , Bali , Brittany , Crete , Ginny Gee , Hawaii , Ingrid Mehlquist , Martha Isaacson , Normandy , Peter Tigerstedt , Pink Trumpet , Professor Hugo de Vries , Red Head , Rocket , Serenade , and Vernus . Certain varieties , namely the Caroline and English Roseum cultivar , are kind of genus Phytophthora source waste unless their grunge is too wet .

Other control condition measures let in found a one - year quarantine point when unexampled plants are bring out to the garden , improving drain in garden layer or containers using raised beds if the dirt drainage can not be sufficiently better , water works at the base so moisture does not splash foliation , keep the ground clean of plant junk and disposing of potentially infect debris or dirt properly , diminish salinity in soil and piss source and sterilise garden shaft . Fungicides may be used as a preventative intervention .

Rhododendrons love acidulous territory — a pH level between 4.5 and 6.0 is acidic enough for them to really thrive . If you are n’t sure of the pH level of your garden soil , you may read about how to find out in our articleHow to try pH in Your Soil . If you ’ve planted a rhododendron in alkaline soil ( that ’s when the pH level is above 7.0 ) , the plant life is in all likelihood taking in too much calcium while simultaneously lack branding iron .

you may amend the soil with acidifying treatments such as atomic number 13 sulfate , elemental sulfur , ferrous sulphate , branding iron chelate , or branding iron sulphate . Top the soil with these handling , and they will become incorporate with the soil as you water the plants or pelting falls . For quick result , you may mix these amendments with the top few inch of soil , but take care to stay shallow so you do not damage the root systems of your plants . you may also opt for water soluble versions of these acidifying treatment , which can be administer using a theme feeder .

If your garden has any alkaline areas , transplant your rhododendron there may be the quickest , easiest solvent . Nourishing your dirt and acidifying it by applying a layer of two to four inches of acidic organic cloth , like well rot compost , peat moss , or leafage mulch , can also help correct discoloration of foliage . you may also rise rhododendron in a container , which gives the gardener over control over the soil .

chickenhearted foliage is also a symptom when the rhododendron has itsroot testis planted too inscrutable . This is an sluttish mistake to make , because burying the solution musket ball at a profoundness that would be the standard for most plant will be too deep for a rhododendron . For best results , situate your rhododendron so the root ball is level with the Earth’s surface of the stain where you could experience it if you run your hands over the land around the plant life . If your rhododendron is planted too deeply , just dig it up so you may make alteration .

Your rhododendron ’s leaves may also sprain sensationalistic if the plant ishungry for fertilizeror athirst due toinsufficient water . Give rhododendrons an annual STD of fertiliser between later May and June . ( Or , if you miss the ideal window for fertilizer app , you may do the intervention at any time of year . ) If you mistrust a lack of water to be the cause for discolored leave-taking , give your plant life a cryptical lacrimation and watch to see if the problem improves .

While you hold back for territory amendments or other gradual solutions to kick in , you could use foliar feeding as a straightaway fix to correct the colour of your rhododendron ’s leave . Spray the foliage with an Fe compound , such as smoothing iron chelate , Fe sulphate , or a soluble constituent Fe complex . Give the plant life a dose of several jet every two to four weeks . While this is a cosmetic remedy that does not purpose any way out with the soil that may contribute to discolored foliation , it ’s a quick hole that can keep your rhododendron vivacious and green for a time of year as the more long - full term treatments do their magic .

If an branding iron discussion has the opposite of its intended effect and your plant life ’s foliage turns even more yellowed , then you are probably dealing with a manganese insufficiency rather of a want of atomic number 26 . ( Do n’t forget that when foliage turns xanthous , poor drainage is another potential cause , for which the best prescription is transplantation to a location that volunteer good drainage . ) Leaves may also plow yellow as aresponse to chemical discussion , so if you ’ve recently spray an insecticide or other chemical near the industrial plant , you may have get the perpetrator .

get the most out of your rhododendrons mean amending and treating the grunge prior to planting and picking out the best possible emplacement . If you amend properly and peck a location that provide your rhododendrons with an ideal growing environment , caring for the heyday becomes a very simple outgrowth . All rhododendrons need , aside from ample territory and a good localisation , is uniform watering , deadheading , and a very occasional pruning . When flora tending need very small movement and slight to no stress , gardeners can really relish their spare-time activity to the fullest extent . Rhododendrons offer month of colouring and ornamental beauty and they are one of the easiest flowers to grow , which construct them a very popular selection for efflorescence gardens around the world .