If you are looking to learn about planting and maintaining azaleas, you are also in the right place, since azaleas are types of rhododendrons.
You can skip to any section quickly using our advanced jump below, or read the full guide to become a rhododendron expert.
Let’s start by answering the most basic question and explaining what rhododendrons are.
Rhododendron is a genus that contains 1,024 species of deciduous and evergreen plants. It is part of the family Ericaceae, which is the heather family.
They can take the form of either large shrubs or (usually) small trees, with their heights varying wildly. Some measure less than half a foot, while others soar up to 100 feet.
If you think rhododendrons and azaleas look alike, you are correct, because azaleas are a subspecies of rhododendron.
Rhododendrons have a huge native range, comprising parts of North America, Asia, Europe, Russia, and even Oceania.
Here are some top reasons to plant rhododendrons and azaleas in your perennial garden:
● Quickly and easily give your landscape a whole new look. Even one rhododendron can help you to restructure your space and attract the eye with bountiful bright blossoms. Indeed, you probably have seen azaleas in formal gardens before. You can enjoy some of that same stately elegance in your own backyard by growing these perennial bloomers.
● Increase your privacy. If you are tired of looking at your neighbor’s ugly yard or of them watching you while you are trying to enjoy your outdoor spaces, planting some tall rhododendrons is a great way to screen them out.
● Rhododendrons are often evergreen. That means you can enjoy their privacy-enhancing benefits year-round, as well as keep some color in your yard when other plants die back for winter.
● Find a plant to fit any space. With most perennials, there is a fairly narrow size range to choose from for any given species or genus. But the size range for rhododendrons is huge. Whether you want to fill a massive empty patch in your yard or you just want a compact plant you can squeeze into a container, you will find exactly what you are looking for somewhere in the rhododendron genus.
● Repel thrips and some other insects. If you already are growing other plants, you know what a pain thrips can be. You will be delighted to learn that rhododendrons will not be bothered by them.
● Rhododendrons are drought-tolerant. If your area is subject to dry spells, they should survive them nicely with a little help from you.
● These plants can stand up to heat. Scorching days now and again will not be an issue so long as your rhododendrons have some afternoon shade.
● All in all, rhododendrons and azaleas are low-maintenance plants that are easy even for beginning gardeners to grow.
● Despite not receiving a lot of attention for it, rhododendrons actually make exquisite cut flowers.
● Propagating rhododendrons is easy. So, when you invest in one rhododendron, you will get a lot of value for it. Within a few years, you should have multiple plants, and all of them will live a very long time.
Rhododendrons are spring-blooming plants. The earliest bloomers among them are generally those that are classified as azaleas. Their blooms will usually appear in April.
How Long Do Rhododendrons Bloom?
The blooms on rhododendrons and azaleas are pretty fleeting; they will reward you with their beauty for several weeks before fading.
Some types of rhododendrons can bloom more than once per season. Deadheading may help you to stimulate a second flush of blooms.
You can also try planting multiple varieties of rhododendrons in your garden that have different bloom times. That way, as one plant’s blooms begin to fade, another may be coming into its full glory. In this way, you can extend the overall bloom season.
How Much Sun Do Rhododendrons Need?
Full sun to partial shade is generally suitable for rhododendrons, but the ideal conditions depend on the type of rhododendron you are planting.
For example, while most rhododendrons do best in full sun or dappled shade, there are a few that can flourish in deep shade.
Additionally, the hot afternoon summer sun can have a detrimental effect on the foliage of some rhododendron species. To prevent leaf scorch, you will need them to receive some afternoon shade.
What Type of Soil is Right for Rhododendrons?
While rhododendrons like the soil moist, it should not be waterlogged. So, plant them in well-drained soil. Additionally, you should make sure that it is relatively rich.
One more thing to know about rhododendrons and soil is that these are acid-loving plants. An ideal pH is 4.5-6.0. That is significantly more acidic than what a lot of other plants prefer. So, if you have alkaline soil, you are going to want to amend it so that it becomes acid soil.
What should you do if your soil is too alkaline? The Royal Horticultural Society suggests, “With neutral or slightly alkaline soils, chelated iron can be used. Ericaceous compost, chopped bracken, and pine needles at planting, plus a dressing of sulphur, may also enable rhododendrons to be grown. Aluminium sulphate (found in hydrangea ‘blueing’ agents) should not be used to acidify soils where rhododendrons are to be grown.”
Another option suggested by RHS is simply to set up some raised garden beds. This gives you better control over the soil conditions.
How Much Water Do Rhododendrons Need?
When you first plant your rhododendrons, they will need more water than they will in the long run. For the entirety of the first season, they will still be establishing. So, you will need to water them twice weekly.
In the future, you will discover that rhododendrons rarely need manual watering. If dry conditions persist for 2-3 weeks, then you will need to water them.
How to Plant Rhododendrons
When you plant a rhododendron, you start with a nursery plant. Prices can vary pretty widely for rhododendrons depending on the species and variety you choose. Not surprisingly, they can sometimes be rather expensive, since some of them qualify as trees. But as they will bloom for many years to come and help you to dramatically transform your landscape, they offer you a good value.
Here are the steps for planting rhododendrons directly in the ground.
1. Pick a location for your rhododendron or azalea plant. Amend the soil as needed (i.e., by mixing in compost).
2. Make a hole for your plant. It needs to be pretty large to accommodate the rhododendron, but keep in mind that it is more important for it to be wide than deep.
3. Place the plant in the hole and backfill the soil. Do not plant it too deep.
4. Water well.
Like many other perennials, rhododendron, and azalea plants can benefit from extra water during the phase where they are establishing.
As some rhododendrons are actually quite compact, they can work well as container plants. Let’s go over the steps to add a rhododendron to your container garden.
1. First, select a suitable container for your potted rhododendrons.
You can use the size of the nursery container to figure out how big your rhododendron’s new home should be. Just add 30% to the size of the nursery container, and that will be ideal.
There are two other important considerations for rhododendron containers. The first, of course, is the presence of drainage holes, which are essential.
The second is the shape of the container. Pick one that is shallow and wide, as this shape is ideal for accommodating the root structures of rhododendrons.
2. Start filling your container with potting mix. In fact, there are actually mixes out there that are sold specifically for rhododendrons and azaleas.
3. Carefully remove the rhododendron from the nursery pot and transfer it into the new container. Fill in the potting mix around it. Do not plant it too deep.
4. After you have finished potting the rhododendron, you should put a little bit of compost on top of the potting mix. Do not push it right up against the plant itself, though.
5. Water well.
6. Move your rhododendron container to where it will receive the right amount of sun.
How to Propagate Rhododendrons
You cannot divide rhododendrons or azaleas, but there are quite a few other options to propagate them. Below, we discuss propagation from seeds, cuttings, and more.
Starting Rhododendrons from Seed
The easiest way to get started with rhododendrons in your garden is with nursery plants. But if you want to propagate them and save money in the future, you can try growing them from seeds.
Be warned, however, that while propagating rhododendrons from seeds is not necessarily “hard,” it does require the utmost care and attention to detail. There are quite a few steps involved, and you need precise control over the moisture, heat, and lighting conditions throughout the process.
In fact, going over the directions in detail is a bit beyond the scope of this post. For that reason, we will turn your attention toward this guide by the American Rhododendron Society.
That post describes the exact process that the society uses so successfully. So, if you replicate it, you should also be able to propagate these perennial shrubs and trees using the same techniques effectively.
If you are looking for an alternative set of directions which also features an impressive amount of detail, see this post.
Starting Rhododendrons from Cuttings
Here are the directions for propagating the majority of rhododendrons from cuttings:
1. In early autumn, remove some cuttings from new growth in the morning. Ideally, you should use soft wood, as this will increase your chances of rooting successfully.
2. As usual, you should remove the leaves from the lower part of the cuttings, as you would if you were using the method for most other plants.
3. On both sides of the cuttings, you should carefully strip away the top layer of bark around the bottom inch or so.
4. Dip the ends of the cuttings in rooting hormone. Make sure you use a product that incorporates a fungicide.
5. Fill flats with a 50/50 mixture of milled sphagnum moss and perlite or vermiculite.
6. Insert the cuttings into this mixture.
7. Cover the cuttings with a clear plastic bag or container, but make sure that there is no contact between the cover and the cuttings. That way, you lock in moisture, but do not encourage rot.
8. Find a location for the cuttings to root where they will be exposed to indirect light only. Apply heat at the bottom to maintain a temperature of 70-75 degrees Fahrenheit.
9. It is going to take quite a while for the cuttings to root—anywhere from 6 weeks to 4 months, depending on what type of rhododendron or azalea you are trying to propagate.
During that time, you should regularly check on the cuttings to make sure they are not drying out, adding water as needed. A couple of times weekly, you also should rotate them. This will ensure that they are receiving light evenly while they are developing their roots.
10. Transplant the new plants once they have rooted successfully.
You should be aware that if you want to propagate deciduous azaleas using cuttings, the right time to take the cuttings is in June rather than during fall. Additionally, the process is a little bit different, and a bit harder to succeed with as well.
Other Propagation Techniques
There are a number of other methods that can be used to propagate azaleas and rhododendrons. These include cloning, grafting, layering and tissue cultures.
How to Care for Rhododendrons
One of the best things about rhododendrons and azaleas is how easy these plants are to maintain. You might not expect it, but their needs are minimal with respect to pruning, staking, mulching, and fertilizing.
How to Fertilize Rhododendrons
We have seen different advice regarding fertilizing rhododendrons from different sources. So, we will turn to the recommendations from the American Rhododendron Society.
The society says that if you are growing these plants in rich soil, then you do not need to fertilize them. But if the soil is not rich, then it is a good idea to apply fertilizer in early spring. But you should not overdo it. Rhododendron plants are quite sensitive to fertilizer. Applying too much can even be deadly.
The site provides some detailed information about various minerals, so it is worth taking a look if you want to get specific about fertilizing your rhododendrons and azaleas.
How to Mulch Rhododendrons
Mulching rhododendrons and azaleas offers quite a few benefits. You will conserve soil moisture, regulate soil temperature, and reduce the chances of the soil getting compacted by harsh weather.
Organic mulches are great for these plants, because they get the job done while increasing the acidity of the soil.
If your climate is pretty temperate, the best time to mulch around your rhododendrons or azaleas is in spring. Wait for the soil to get warm, and then add your mulch layer before it dries out. You want to preserve the moisture as much as possible. You should mulch again in autumn.
In colder climates, spring/summer mulch is not as important (unless it is particularly dry and/or windy where you live), but autumn mulch to insulate the soil during winter becomes even more vital.
How to Stake Rhododendrons
Good news—rhododendrons and azaleas are sturdy shrubs and trees, and do not require staking in the vast majority of cases.