How to Plant, Grow and Care For Rhododendrons

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When the early spring garden still looks winter bare, you can always rely on rhododendrons to brighten the landscape. This shrub has big branches with masses of colorful blooms that emerge early in the spring and never disappoint.

For a low-maintenance plant, rhododendrons provide an impressive wall of color. Get the basics right and rhododendron blooms will be a mainstay in your garden.

If you want an explosion of color that doesn’t require a huge amount of work, try rhododendrons and you won’t be disappointed.

Are you ready? Then, let’s go.

What Are Rhododendrons?

This wonderful shrub is native to North America, Europe, Asia, and Australia. In other words, pretty much any temperate region has native rhodies. There are around 1,000 wild species of rhododendrons, and well over 1,400 hybrids to choose from.

Rhododendrons have both evergreen and deciduous varieties. Some grow as tall as 25 feet, while others grow low to the ground.

Think color when you consider rhododendrons. They come in a riot of colors and there are wonderful yellows, pinks, whites, purples, and reds.

Rhododendrons can suit USDA Growing Zones 3 to 9, so check which ones grow where you are and pick your favorites. Some rhododendrons are native to the Southern US where they need warm temperatures. Some like cool weather, and others will die if it gets too cold.

Be aware that azaleas are also part of the Rhododendron genus. In other words, all azaleas are rhododendrons, but not all rhododendrons are azaleas. We’ll talk about both plants since they’re similar and require the same care.

9 of The Best Varieties of Rhododendrons to Plant

There are literally hundreds of cultivars and hybrids to choose from, so talk to a local expert about the best ones for your area. University extension services are perfect for this.

Let’s look at some of the best that I’ve had success with and I hope you do too.

1. Rosebay

R. catawbiense is the perfect cultivar to start with if you’re a beginner at growing rhododendrons. It’s hardy, healthy, and puts on a good display.

At around 12 feet tall and six feet wide, this one comes in purple, pink, and white blooms. Catawbiense blooms in spring and is good for USDA Growing Zones 4 to 8.

2. Red Hills

Native to the Southeastern United States, this azalea species is known for being super-fragrant. The buds are pink, followed by white or yellow flowers.

R. colemanii grows well in USDA Growing Zones 6 to 9. It will grow up to eight feet tall and six feet wide. Flowers are at their peak in early to mid-spring.

3. Gibraltar

You will get a stunning display of fiery orange flowers with ‘Gibraltar,’ which is a petite azalea. At five feet tall, you can plant this hybrid in a container and it will be perfectly happy. Full sun or dappled shade is fine.

4. Blue Baron

To preserve the lovely deep blue hue, ‘Blue Baron’ likes shade. The flowers start out as a darker purple, before fading to light blue. It blooms in mid-spring and will grow to six feet but often tops out at three feet. Good in Zones 5 to 8.

5. Nova Zembla

If you have shade to part-shade in Zones 4 to 8, then ‘Nova Zempla’ is a good choice. The bright red flowers attract hummingbirds and butterflies to the garden.

In mid to late spring, ‘Nova Zembla’ is a wall of flowers five feet tall and four feet wide. This is one of the most popular rhododendrons available.

6. Capistrano

This is a mounding and compact hybrid that forms into quite a dense plant. It grows to about four feet tall and produces pretty yellow flowers.

The leaves are evergreen and the flowers appear mid-spring. Plant ‘Capistrano’ in Zones 5 to 8. It prefers a reasonable amount of water so keep an eye on how dry the soil gets.

7. Purple Gem

Looking for a dwarf hybrid that you can use as a border plant? The flowers bloom in mid-spring and are a deep purple to violet.

Give purple gem a little shade, moist soil that drains well, and it will be happy. Try it as a border, on a patio, in small gardens, or where there is limited space that needs color. Plant in Zones 4 to 8, with partial sun.

8. Hydon Dawn

If you have an area with full sun, try ‘Hydon Dawn.’ It’s one of just a few rhododendrons that will tolerate it.

This hybrid grows five feet wide and five feet tall. The pale pink blooms provide a delicate touch to stronger-looking plants around and behind it.

9. Mandarin Lights

In spring, you will get bright orange blooms before the foliage fully emerges. R. prinophyllum ‘Mandarin Lights’ is a hardy rhododendron. Plant in Zones 3 to 7. Provide a little shade and make sure the soil remains moist.

Propagating Rhododendrons

There are a lot of methods that gardeners use to propagate rhododendrons. This is my preferred method because it’s easy and has great results. I use cuttings, but you can also use layering or grafting.

10 Easy Steps to Grow Rhododendrons From Cuttings

  1. Choose a branch that is upright and has a fresh, light green color. Preferably choose one with no bud on it because you’ll have to remove it. The branch should also be pliable, so don’t choose one that is hard and stiff.
  2. Cut the branch about six inches from the tip. Cut straight across the branch.
  3. Remove the bud if there is one, and remove the lower leaves, leaving a few at the end.
  4. If the leaves are large, cut the top quarter off straight across. If the leaves are small, leave them as they are.
  5. With a sharp blade or knife, carefully strip away the bark from the bottom inch of the branch.
  6. Dip the bottom tips into the rooting hormone. If you don’t have any, use honey or nothing at all. Rhododendrons are reliable when taken as cuttings.
  7. Push the branches into your growing medium. Use seed-raising soil or potting mix.
  8. Take as many cuttings as you can and use a tray container because you can plant them close together. Once the roots grow, you will be moving them into other containers or the garden.
  9. Place the tray or containers in a warm area with indirect sunlight. Keep the growing medium moist at all times.
  10. Leave for approximately two months. Tests for roots by lightly pulling on the cutting. If you feel resistance, you have been successful. It’s at this point you can transfer to wherever you are planting them.

Seeds

You can easily grow rhododendrons from seed, however, they will unlikely be the same as the parent plant. Plus, hybrids might be sterile.

If you have a favorite rhododendron and you want the new plant to be the same, use asexual methods like cuttings.

How to Care For Rhododendrons

Although rhododendrons need shade with a little sun, if you live in a warm area, protect them from afternoon sun. If you’re unsure, choose a site with dappled sunlight for at least six hours a day.

Rhododendrons are known to be easy to grow, but they do need specific soil conditions. It must be well-draining, be able to hold moisture, and be reasonably acidic. Aim for a pH of 4.5 to 6.0.

Don’t use too much fertilizer. Give a small amount in spring and that should be enough. Of course, if they are struggling or weak, feed with a 10-8-6 fertilizer. You can purchase fertilizer specific to rhododendrons.

Soil should be kept moist but not wet.

Mulch the plants in spring before the summer heat arrives. Rhododendrons have shallow root systems and can dry out easily. Use pine straw or pine bark, which will slightly acidify the soil as they break down.

Don’t prune rhododendrons unless you really feel the urge. They are a naturally attractive sprawling plant. Prune directly after bloom or you risk not getting flowers the next season. Remove any damaged branches, especially if they are diseased.

You should deadhead spent flowers. This promotes plant growth. Be careful though. Next season’s flowers are directly under the current ones on old wood.

You can grow rhododendrons in containers if they are a small variety or a variety that likes container growing. The most important thing is drainage. Keep the soil moist, but not soaking.

If you live in an area with freezing winters, containers can be moved inside in unheated garages or basements, just so they don’t freeze.

Companion Planting for Rhododendrons

  • Mountain Laurel
  • Witch Hazel
  • Barberry
  • Summersweet
  • Hosta
  • Ferns
  • Narcissus
  • Hellebores

Problems and Solutions for Growing Rhododendrons

Rhododendrons can be affected by a few pests and diseases, but generally, nothing is catastrophic.

Powdery Mildew

This is a fungus that travels through wind due to microscopic spores. Read our detailed article here.

Petal Blight

This is a fungal disease of many flowers, but rhododendrons can be quite susceptible.

You will see light spots on colored petals and brown or darker spots on white petals. As the spots spread, the flower turns into a sloppy mess.

A fungus forms at the bottom of infected flowers before it drops to the ground where it overwinters. Spores are released the next season and spread by wind.

Remove infected flowers carefully before the spots spread. If you have had this issue in the past, use a good fungal spray as soon as buds appear.

Leaf Gall

This is a common fungal disease that can cause distorted growth. Native rhododendrons are sometimes more susceptible than hybrid varieties.

Leaves and buds that are infected begin to distort. They become thickened and curl up. Then, they become fleshy or swollen and turn a light green color. A gall then forms that becomes hard over time.

The gall itself doesn’t do a lot of damage, but it looks ugly. You can pick the galls off once they are hard and brown. Use a general fungal spray next season to try and prevent it.

Aphids

Aphids get into just about every plant. Read all about them here.

Black Vine Weevil

This pest comps on the leaves of the rhododendron, making it look messy. Plus, it weakens the plant by attacking the roots.

The larvae live in the soil and feed on delicate, shallow roots. The adults chew a lot of holes in the leaves. If the soil is too wet for the larvae, they move closer to the soil and often girdle the plant making it hard to transport water and minerals from the soil.

If you don’t see the adult bugs, but see the damage, go out and look at night when they feed.

When you first see the damage on the leaves, use a general pesticide. At the same time, use beneficial nematodes in the soil.

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