How to Grow Rhododendrons (Beginner's Guide)

Rhododendrons (you may have heard them called rhodies) are one of the most popular flowering shrubs in the garden.

And for good reason.

They’re gorgeous! These shrubs are huge and wide with plenty of blossoms, thus making them an excellent plant for void fill or just to really give your garden some colors. They can be blue, orange, pink, purple, or even lavender.

They do take quite some time to reach full size, so you may want to start with a transplant from your greenery if you’re impatient.

But even starting from seed is very rewarding as you can shape the plant however you want. Compact? Freeform? Your choice!

Let’s learn about how to grow and care for rhododendrons. I hope this care sheet helps you get a good grasp of the shrub.

Quick care guide: Rhododendrons

Plant type	Flowering evergreen or deciduous perennial shrub
Origin	Asia, Australia, Europe, America, Spain
Scientific name	Rhododendron ferrugineum"
Other names	Gunnera Azalea Red tree Rhodie
Soil type	Organic, rich, loose, loamy, nutrient rich, well draining
Soil pH	4.0-6.0 (acidic)
Sunlight requirement	Full sun,8 hours daily Partial sun if warmer conditions
Bloom season	Spring to summer
Colors	White, lime, green, purple, orange, magenta, blue, pink, yellow, white, green, lemon, lavender, red
Max height	30 feet
Max width	40 feet
Low temperature tolerance	20F
High temperature tolerance	90F
Ideal temperature range	50-70F
Humidity	High (50% or higher)
Watering requirements	Water when the top layer is near dry
Fertilizer requirements	Supplement throughout growing season, stop during fall, supplement with iron
Plant food NPK	14-7-7
Days until germination	10-21 days
Days until harvest	60-80 days or when the plant have 6-8 leaves (8" tall)
Bloom time	Varies, blooms up to 7 months depending on species
Speed of growth	Moderate
Hardiness zones	USDA hardiness zones 4-10
Plant depth	From seeds: surface plant (0 inches) From transplants: Same depth as original plant
Plant spacing	5-10 feet
Plant with	Mountain Laurel Japanese andromeda Astilbe Kalmia Pierris Viburnum Mahonia Ginkgo biloba Rhody Nyssa Alliums Blueberries Heathers Pines Oaks Wildflowers Hostas Conifers Holly Berberis koreana Pussy willows Bleeding hearts Clethra alnifolia Berberis thunbergii
Don't plant with	Plants that will be outcompeted for nutrients if poorly spaced
Propagation method	Transplants, from seed, layering, cuttings
Common pests	Rhododendron Borers Lace bugs Weevils (multiple types) Spider mites Sawflies Caterpillars Bark scale Aphids Worms
Common diseases	Leaf spot, bud blast, root rot, Botrytis, phomopsis dieback, phytophthora dieback, petal blight, powdery mildew
Indoor plant	No
Outdoor plant	Yes
Grown in container	Yes
Flowering plant	Yes
Beginner friendly	Yes
Care level	Minimal to none (easy)
Best uses	Bordering, edging, pathing, privacy, void fill, container plant, plant cover, plant walls

What’s a rhododendron?

It’s a woody flowering shrub that’s known for its large, pink blooms. These shrubs are extremely popular for their ease of care. Being part of the Ericaceae family, they’re similar to their cousins like the fern or huckleberry.

They require little work but reward you with plenty of those gorgeous purple-pink flowers. They come in a variety of sizes, colors, and shapes. They can even be grown in part shade.

With so many variants, they can handle a variety of climates, soil types, and even garden sizes. They can even be planted in containers!

Versatile. Easy to care for. And gorgeous.

Types of rhododendrons cultivars

There are so many different types of rhodies that you’ll be hard-pressed to find the “perfect” strain- if that even exists!

There’s no single one that works for everyone. Each cultivar has its pros/cons. Some are suitable for larger environments that provide plenty of plant cover. There are over 1000 species.

Others are compact that are suitable for container growing. It’s up to you to find what suits your needs. There’s literally a strain for every garden.

If you’re having trouble deciding on which type of rhododendron to get, think about where you’re planting it, the local temperature, your time/energy commitments, and the amount of space you have.

Here are some popular cultivars to get you started:

America (full sun, 6 feet tall and wide, purple flowers)
Elvira (bright red flowers)
Ramapo (compact, woody, purple)
Rosy Lights (pink, compact, small, cold hardy)
Augfast (dwarf, compact, blue flowers, 3 feet tall, early bloomer)
Top Banana (bright red buds)
Janet Blair (pink flowers, 6 feet tall, drought hardy)
Catawba (broadleaf, dark green foliage)
Nancy Evans (4 feet tall, lots of flowers, yellow/pink hybrid flowers)
Trinidad (cream and red edges)
Nova Zembla (tolerant of temperature highs/lows, 5 feet height, lots of blossoms, orangish flowers)

How to propagate

Rhododendron in garden. — Look at how dark that hue is.

Thankfully, Rhododendron is super easy to grow from seed, layering, or just buying one from the nursery.

This plant readily germinates from seed if you enjoy starting from scratch. Read over each propagation method and see which one suits your style.

If you want the most rewarding way, seed sowing is the only way to go. If you want a head start to enjoy the blooms, then go for a nursery transplant instead.

Starting from seed

This is the easiest way to get started.

Get a packet of rhododendron seeds online or at your local garden center. You need to make sure that you get the right species because hybrids can’t be grown from seed. So make sure that it’s not a hybrid rhododendron. Named cultivars also can’t be sown from seed.

The ideal time to sow is in January or February. They can get a head start for the season if there’s sufficient heat. Use a plant heat mat or a grow light to keep them warm. Start with 5” planters.

Get biodegradable ones if you want to save yourself from more work later on. Plastic holds heat poorly compared to terra cotta or organic materials. Just FYI.

Fill it with any generic potting mix. Use a water-retaining medium. If you want to get fancy, you can, but it’s not necessary because this is just the germination pot. You’ll be replanting your seedlings later on into the soil.

Each 5” pot can hold 2-3 seeds. Place them on the surface, but don’t cover them.

Water well using a spray bottle. It’s important to use distilled water only. Soak the water with continuous spraying until it’s nice and moist. The seeds will soak into the soil over time. There’s no need to pat them down.

At this point, just keep the soil moist. Avoid letting it dry out at any point or else you’ll kill the seeds. Temperatures that are high will halt germination. And it won’t germinate either.

Spray 2-3 times daily to keep it moist. You can use a humidity dome (or a plastic cover) to help trap the moisture so you don’t have to water as often.

Place the pots under grow lights or near a sunny window. They need at least 8 hours of direct sunlight daily.

The seeds will germinate in about 10-21 days. Germination time will vary. It depends on the local climate, temperature, watering conditions, sunlight, and cultivar too.

So be patient if you don’t see seedlings in 10 days.

After they germinate, continue the same care regimen. In 8 weeks or so, you should have at least 2 pairs of true leaves. When this happens, it’s time to harden them off by exposing them to the outside elements.

Only do this when the last frost has passed. If not, keep them indoors. Continue to keep them moist, and warm.

When the temperature remains around above 50F or so, it’s time to bring them out to their new home in your garden!

Bring them to your yard for a few hours daily. Put them in the sun for about 6-8 hours. This will get them used to the outside. Do this for 2 weeks or so.

Start with just minimal sunlight exposure. Then increase by an hour every day. Keep the soil moist at all times until you complete the transition.

They’re now ready to go into the yard! Uproot them gently and then sow them into the soil. Be sure to use high-quality soil that’s nutrient dense with moisture-retaining properties.

Starting from cuttings

Propagating from cuttings is the quickest way to get started if you want to grow hybrid rhododendrons. Start in the late summer or fall.

The cuttings should be taken at the heel in the early morning only. Use new cuttings that are still pliable. They should not be hardened. The softwood is less likely to rot after you cut them. If you cut the harder woods, they’ll be prone to rotting. They don’t root well either. So it’s a double negative.

The key to finding the right stem is that it should be younger and has multiple leaves. If it has flowers, that’s fine. Take the cut. Remove any flower buds or spent ones.

Keep only the top few leaves on the stem. Use a sharp, sterilized knife to cut the outer green shell on the bottom 0.5” of the stem. This will expose the interior so it’ll root easier. Use a rooting powder or gel if you wish.

Next, fill a pot with a 50/50 mix of vermiculite or perlite with peat moss to help it root. Peat moss is usually discouraged, but rhododendrons crave it for rooting. Water it until it’s wet. Place the cutting 0.5” deep into the soil and then cover it with a humidity dome.

Place the pot on a heat mat to keep it warm. Continue to keep it moist, but never wet. Spray it daily. Never let it go dry. Keep the temperature within 50-60F. New roots will form in about 6-8 weeks.

You can check to see if your stem has rooted by gently pulling on the stem. If it doesn’t give, then it’s done. If it comes out, check for rot before you reinsert it. Continue to wait for another week.

When it’s rooted, you can move it to your garden!

By layering

Layering is another method that works really well with rhododendrons. In the early fall or late summer, find a low-growing branch and use a sturdy wire to pin it to the soil. You’ll have to bend it to get it to sit.

The point is to keep it pinned into the soil using whatever you have. Keep the bent branch in the soil. Cut off any leaves in the section that’s pinned.

Water it and feed it as you do for the entirety of the plant. Layering basically makes the bent part grow into its own plant. It takes a long time for it to finally root (as in years). So if you want to do this, you’ll need patience. It also only works if you already have a rhododendron plant going in your garden

The roots can be checked the same way as checking a cutting. Give a tug to see if it gives. If not, it’s rooted. If it does, pin it back and let it be.

Once the roots have formed, clip the branch closest to the bush. Dig up the new plant. Clip it on both sides using pruners to release it. Then plant it on its own. It’ll need about 5” of depth, with 10” around. Plant it like a regular transplant.

By transplant

This is the prefeed method if you want to enjoy those blooms quicker. Just buy a good shrub from your local garden center then transplant it into your garden. Try to plant at the same depth as the pot it came in. Provide ample space around it and water it generously.

Use compost to help keep the soil well draining. Try to provide 5 times the width of the container.

The depth can be up to twice the original container depth. But don’t plant too deep because this can harm your shrub.

Don’t remove any of the debris that’s stuck on the roots either. They have beneficial bacteria. You can prune after you’ve planted and given it a few days to harden off.

How to grow

Yellow rhodie petals. — This color? My personal fav.

Rhododendrons are extremely easy to grow and tolerate a variety of conditions- everything from shade to full sun. I’ll try to get you a summary of the ideal conditions so you can get the most out of your plant.

They grow bigger with more blossoms and numerous flowers if they’re grown correctly. But it also depends on the cultivar type.

The following sections contain tips to maximize the flowers per annum.

Hardiness zone

This woody shrub is perfect for USDA hardiness zones 4-10. But even if you’re slightly outside the suggested hardiness zone range, you should be fine if you opt for a cultivar that’s less sensitive to warm or cooler temperatures.

You can also plant in shadier spots if your zone is too warm. Or you can use mulch or plant protection if it’s too cold.

Soil

Rhododendrons prefer soil that’s well-draining, moisture-retaining, and with plenty of nutrition.

They love humus, so consider supplementing some into your substrate. The soil can be clay, sandy, or loamy. They’re not picky as much as the pH.

Soil pH

This plant is quite picky when it comes to pH. Rhododendrons prefer acidic soil with pH values between 4-6. If the soil isn’t acidic, it will produce poor blossoms.

The soil can be amended with pH down to bring it to a more favorable range. The soil can be mixed with pine bark to help drop the pH. Or you can grow in a pot with primed soil.

Some compact hybrids can be grown in containers with the right soil. Use ericaceous soil/fertilizer.

The majority of gardeners will use sulfur-based soil supplements to help lower pH. Use a soil meter to test the acidity. It should be acidic, but never basic.

You’ll need to adjust the soil levels to get the most out of your plant. Results will vary depending on the soil type. Avoid using aluminum sulfate because it’s based on sodium, which doesn’t take well to rhododendrons. They hate salt in the soil.

Depth

For seeds, sow at the surface. For transplants, use the same depth as the original planter.

Spacing

Space each plant at least 5 feet apart. Bigger cultivars should be spaced up to 10 feet apart to reduce them fighting over nutrients. These guys can grow upwards of 30 feet tall and 30 feet wide. So give adequate space.

Temperature

Temperatures between 50-70F are a good range. When temperatures drop to the 40s, you’ll notice that the foliage will begin to droop.

They won’t curl until the temperatures drop to 32F. But even then, your shrub will be okay. They can handle temperatures as low as 10F as long as it’s not for extended periods.

On the other end, they can tolerate heat too. Temps as high as 90F will be fine. Some cultivars can tolerate heat, but most will prefer just warm and humid environments.

Humidity

These shrubs don’t like wet feet. If the water pools and doesn’t drain, it can cause rot issues.

You should keep humidity moderate to high, but with plenty of space for water to evaporate.

This can be achieved by regularly pruning dense foliage, using a good-quality substrate, and not overwatering.

Watering

These plants can handle a lot of water, but even then, you shouldn’t go crazy with them. It’s possible to overwater rhodies. If you do it often, it can severely damage your plant.

But if you don’t want enough, the same goes both ways.

So find the happy medium and go for that. Use a soil moisture meter if you don’t know how much to water. You’ll want to keep it moist at all times, but never wet or fully dried out. If the soil doesn’t drain well, it can also lead to pooling water at the base.

Overall, rhodies need a lot more water than your typical garden plant. They’re native to the northwest, which rains a lot. These plants will need plenty of water when young.

Established plants will need less. So you can taper off as needed. Signs of not enough water are obviously no blossoms. If you don’t see buds forming on the leaves, browning leaves, or curled leaves, your shrub needs water.

During the spring and summer, never let the top 1” of soil get dry.

If the fall, start reducing the water volume. This will get it ready for the winter. Water less during this time. The soil should be moist before the cold season to help protect the roots.

This is the only time you can let the soil get dry. Then soak it up! This will prepare it for the first freeze within the next day or so. It needs that water to help protect the roots from the cold. Easy enough.

Fertilizing

Rhododendron requires a good amount of plant food to help encourage the strong growth of the branches and produce those pretty flowers.

Ideally, you should fertilize in May and stop in July. If you fertilize too late in the season, your Rhodie will produce new branches which will be harmed by the cold weather. Therefore, you only want it to feed during the spring or summer.

The fertilizer should be diluted and acidic. Look for an NPK of 14-7-7 or something high in nitrogen. It needs N to produce leaves. Work it gently into the base, but don’t go into the root system. It can build up and cause damage.

The soil around the plant should be replaced regularly and weeded too. pH fluctuations will cause the soil to become alkaline over time too. You’ll have to apply soil amendments to keep it slightly acidic. A soil test kit can solve all those problems.

Sunlight

If it’s too shady, your rhododendron will produce buds but they won’t break. This means no flowers.

You’ll need full sun for at least 8 hours daily to get those precious blossoms. If it’s hot in the summer, protection from that scorching is necessary.

Ideally, they should be placed somewhere with early morning sun, followed by afternoon shade. You can use filtered or dappled light for the afternoon by using artificial shade.

While they can grow in the shade, you’ll need full sun to get the blooms. If you’re in a warmer zone, you can plant it in partial shade or grow a cultivar that’s more drought-tolerant.

Wind

Rhododendrons are prone to toppling over from the wind.

They can also get severely damaged by strong gusts. They should be on the eastern side of the oaks or pines. This gets them protection from winds plus they get that morning sun with dappled shade, followed by the evening sun.

That’s the perfect combo to get them producing their signature blossoms. This plant prefers sloped surfaces because the water drains well and they get some wind protection.

Too much wind can break flowers, and buds, and even topple them. Leaf burn is also common from the wind.

Pruning

Rhododendrons require very little pruning. In fact, deadheading is completely optional.

If you’ve cared for other plants like hollyhock or oleander that require deadheading, you’ll be glad to know that you don’t do it for your shrub. Your plant will blossom and bloom without pruning.

If you want to prune, use sterilized pruners. Some people like to keep it shapely by pruning off stems. You can also remove spent flowers or branches that are damaged.

Remove the spent flowers in the summertime. There’s no reason to keep them on your plant because they just waste energy and attract pests. It’ll also help encourage larger blooms next season. Stop pruning in August onwards.

Pruning to keep it compact is key to making them look good. If you want, you can keep them tidy by doing a hard prune. Cut them back.

They won’t get harmed by it. It may even encourage more flowers. Rough-barked can handle more pruning than smooth-barked. Even potted shrubs can be pruned with no damage.

Mulching

Mulching should only be done sparingly.

The reason is that they have shallow roots that can be damaged easily.

Heavily mulch can be used on days with temperature dips, but avoid letting it touch the stem. If it does, it can lead to rot. Only use shredded pine bark, straw, or leaves from oak.

Try to only use pine or oak products. 2-3 inches of mulch and extend it beyond the drop line. This should be good enough to mulch your shrubs. It helps retain moisture and also protects the fragile roots from temperature swings.

Buds not blooming?

Buds that form, but don’t bloom are usually due to some kind of watering problem. Shrubs that are under or over-watered will cause the buds to never bloom.

If they break or split but no flower comes out, check your watering regimen. Hot and cold fluctuations can also cause them to not bloom. Bark splitting is also a sign of temperature swings.

You can wrap the plant in burlap or mulch it to help keep it insulated from the temperature.

Can you grow rhodies indoors?

Rhodies are large shrubs that can’t be grown indoors. The only time they should be inside is during seed germination or during the winter (if potted). Otherwise, they need sunlight from your garden for 8 hours a day.

How about containers?

The compact varieties of rhododendrons can be planted in pots. The pot should be large enough to accommodate the roots. Thankfully the roots are quite shallow. The only problem is drainage.

You must use well-draining soil with multiple drainage holes in the pot. The pot should be large enough so that it does get rootbound. Otherwise, care is pretty much the same.

Note that potted plants require more frequent watering compared to soil-sown plants.

Companion plants

Rhodes can be paired with many different shrubs. Some of the most popular companion plants include the following:

Mountain Laurel
Japanese andromeda
Astilbe
Kalmia
Pierris
Viburnum
Mahonia
Ginkgo biloba
Rhody Nyssa
Alliums
Blueberries
Heathers
Pines
Oaks
Wildflowers
Hostas
Conifers
Holly
Berberis koreana
Pussy willows
Bleeding hearts
Clethra alnifolia
Berberis thunbergii

Find shrubs that do well in light soil with acidic pH. Evergreen perennials that require full sun exposure will generally be suitable plantmates.

Don’t plant with

There are few plants you want to avoid planting with rhodies, such as walnut or other shrubs that aren’t good at nutrient absorption.

The reason is because rhodies are good at taking up all the nutrition in the soil which can outcompete other nearby shrubs or plants. The leaves also take a long time to break down too. So this can cover up nearby plants which blocks energy production.

Pests

These shrubs are pretty hardy against bugs and don’t suffer as much as their cousins (roses), but there are still a few bugs that you’ll need to watch out for.

Here’s a short list of common insects that you’ll find on rhododendrons:

Rhododendron Borers
Lace bugs
Weevils (multiple types)
Spider mites
Sawflies
Caterpillars
Bark scale
Aphids
Worms

The majority of insects are caused by overwatering or overfeeding. You can control most of them by manual removal, organic insecticides, or using beneficial nematodes. Rodents, deer, or other creatures have been spotted nibbling too.

But established plants are resilient to pests.

Rhodies are very resilient towards pests, so you’ll have time to see what works for you. I suggest starting with manual removal as this can damage their numbers by a huge margin. Then move to insecticides if necessary.

Diseases

There are also a handful of issues you should be careful of that can infest your shrub:

Leaf spot, bud blast, root rot, Botrytis, phomopsis dieback, phytophthora dieback, petal blight, powdery mildew, etc. These are common but can be treated with regular pruning, removing of infested leaves or branches, and reducing watering.

You may need to use a copper fungicide to help eliminate rot problems.

Usage scenarios

These shrubs are excellent for plant cover with their huge, voluminous blooms. Use these shrubs to build a privacy wall, foundation plant, or plant color. They can also provide shade for shorter plants. Use them for plant borders, pots, etc.

They’re simple to grow and will produce flowers every season. If you want a plant that’ll cover the sides of your garden or void fill, this is it. They offer plenty of coverage with some cultivars going over 40′. That’s a wall of flowers indeed.

Enjoy your rhodie

Purple rhododendron flower. — Purple rhodies are always nice.

Rhododendrons are versatile shrubs that are excellent for newbies.

These colorful, large shrubs can be used for a variety of purposes. With their ease of care and amazing flowers, it’s no wonder why they’re favored amongst those in the hobby.

How will you use your shrub? Post your thoughts!

Steven Pham

I took interest into microflora and microgreens before it became mainstream. The idea of growing an entire ecosystem on a tiny scale simply was astounding. That’s where I discovered that I actually like raising plants and wasn’t as much of a black thumb as I thought. Now, I’m relaying what I’ve learned to others who are getting into the hobby in a way that anyone can understand.

How to Grow Rhododendrons (Beginner’s Guide)