How Fast Do Rhododendrons Grow? (Plus Tips to Grow Them Faster)

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The opening to Daphne du Maurier’s Rebeca features one of the most famous depictions of rhododendrons of all-time as they twist their way around into the Unnamed Narrator’s imagination as she imagines how the famed Manderley estate’s “Rhododendrons stood 50 feet high.”

The rhododendrons at Manderley itself are no less imposing, being described as being “twisted and entwined with bracken” as though in an “alien marriage with a host of nameless shrubs” while appearing like looming “slaughterous red, luscious, and fantastic” flowers an invasive strangling presence much like the book’s Rebecca herself.

Whether you imagine your own rhododendrons becoming similarly imposing and unruly or want to keep them trim and in check, there’s no denying that they have the ability to grow quickly and overspread in an area when left to their own devices.

Of course, in certain situations, you might wish to grow your rhododendrons faster, while others may call for slower, more controllable growth.

Whatever your rhododendron growing desires may be, this guide can help you achieve them and grow a full bloom of rhododendrons worth remembering.

Rhododendron Overview

To know how quickly or slowly you can expect them to grow, you first have to know what you’re working with when growing rhododendrons.

They are flowering plants that boast tubular or bell-shaped flowers that are fragrant. Their leaves tend to be on the larger side.

They grow best in climates that are mild yet enjoy a fair amount of rainfall in summer, so one prerequisite for getting them to grow quickly is to avoid dry planting conditions. Rebecca is set in England, which frequently enjoys muggy moist summers, and while you may not enjoy that weather yourself it is ideal for rhododendrons.

This is also why rhododendrons tend to grow quite well in parts of Canada with a similar climate or in hot and humid states within the United States such as Florida.

You’ll also want to know which variety of rhododendron you’re dealing with. Some rhododendron shrubs can indeed grow to the massive heights described in the book, while others are more low-growing in nature. Knowing the type you have can help ensure that you are caring for it the right way.

You’ll also want to know when the variety in question flowers. Some do so on the earlier side, around March, while others flower late in July or even a tad later.

Either way, rhododendrons do best when planted in locations that offer both exposure to sunlight as well as plenty of shade. The soil in which they grow should, like the climate, be moist. In addition, it should be mildly acidic, around 4 to 6 on the pH scale.

Size Categories and Growth

As alluded to above, not all rhododendrons are the same. You thus want to make sure you find the right type of rhododendron for keeping with your growth expectations.

For example, some grow up to one foot long, while others can exceed three feet in height. According to the National Gardening Associations, rhododendrons have the ability to grow as much as 20 feet in a single season.

Naturally you’ll want to judge the growth rate for these rhododendrons differently than for smaller variations.

General Tips for Speeding up the Growth Rate

While different types of rhododendrons require different degrees of attention and can grow to different heights, there is still some basic advice you will want to follow when trying to maximize the growth rate for any of these variations.

For example, you’ll want to make sure that their soil is moist enough, which means regularly watering it, even if you do live in a humid, moist climate.

While you don’t want to drown these plants, providing them with enough moisture is essential for making sure that they not only grow faster, but that they grow at all. Denying them moisture is a fast way to stunt the growth and development of these plants.

As mentioned above, you also want to make sure that your rhododendrons also have a decent amount of exposure to sunlight. After all, those large leaves and relatively large blooms don’t sustain themselves. They need the help of sunlight to help feed them and keep them healthy.

That being said, you also don’t want these delicate buds and leaves to be exposed to dry, hot conditions, so make sure that there is at least some shade nearby that can be employed to protect them on days where the sun is too searing for them.

To that end, timing your plant’s sun exposure can also help them grow healthy without frying them in the hot, dry sun. For example, exposing them to sunlight bright and early in the morning when it is less hot and intense can help ensure that they get enough sunlight for the day if you have to shade them from searing hot temperatures later.

Potting Them Properly

As mentioned, you want to make sure that you plant your rhododendrons in the best possible manner so as to ensure that they remain in good shape when you expose them to the elements. As mentioned, this means planting them in soil that is moist and mildly acidic.

In addition, you’ll want to make sure that the soil is deep enough to cover your rhododendrons’ root systems, which are typically on the shallow side. Failure to do this can result in your plant drying out prematurely.

Giving Your Plant Space

As mentioned, the rhododendrons grow to overtake much of Manderley in the Unnamed Narrator’s dream. That isn’t just the book’s hyper-stylized hyperbole and Gothic symbolism at work, but a fair warning of just how much space these plants can take up.

Rhododendrons are not the kind of plant that is good at sharing space with other plants, so you want to make sure that they have their own space. Not only will this help them grow even faster, but it can likewise keep them from encroaching on another plant’s soil and roots.

Ideally, you should give your plants at least two to six feet worth of space all around. If you are planting multiple rhododendrons, you’ll need to make sure that each one has sufficient space not just at the beginning but as the plant grows and its roots spread out beneath the soil.

This is yet another reason why it is important to make sure that you are planting these in such a way as to facilitate long-term growth, which means making sure that the roots are deeply set into the soil.

These plants need to be potted in deep soil that can give them plenty of room to grow and spread out.

The Little Matter of Mulch

One of the trickiest parts of managing how fast or slow rhododendrons grow is the question of mulch.

On the one hand, it can be worthwhile mulching the area in which they are growing.

If you do choose to mulch the soil in which your rhododendrons are growing, you’ll want to do so about once a year. Doing this can help bring some nutrients to and protect the root system while ensuring that the soil remains as moist and fertile as necessary.

That said, one common mistake is to simply lump on massive amounts of mulch. This can be known as a “mulch volcano” to some, and it’s something you should avoid at all costs. Not only will this not help your plant, but it will likely stifle its growth.

You thus want to make sure that you are not smothering your rhododendron with your mulch but only applying as much as is necessary to keep its roots and the soil in which it has been planted in good condition.

Proper Pruning

Too much of a good thing can prove pretty bad for plant growth. That’s true of mulch volcanoes, and it’s true of pruning as well.

You want to prune your rhododendron pretty sparingly, only doing so a little bit every year, excluding emergency pruning to avoid rot or other plant illnesses.

Boundless Growth

Finally, it is important to note that rhododendrons do not stop growing at a certain height.

Left unchecked, they will continue to grow and grow, and as alluded to above, they can reach pretty massive sizes. You thus need to account for this when considering rhododendron growth.

To maximize growth and make it go faster, you need to “plot ahead” and plant it in a plot that is already set up to handle a bigger form of the rhododendron than its current state. This can help accommodate the near-infinite growth that rhododendrons enjoy.

Whether you imagine them as symbols of romance, metaphors for an encroaching all-consuming presence, or simply a beautiful and intriguing flowering plant, rhododendrons can be an exciting addition to any garden, as long as you plan ahead and accommodate them properly.

By following these steps, you can not just speed up your rhododendron’s growth but boost it toward its fullest potential, helping get the most out of their massive looming lovely presence.

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