How to Fix Yellow Rhododendrons (and Azaleas and Pieris, Too)
Although there could be a number of reasons why your rhodies are lying in the rough with yellow foliage, a combination of high soil pH and a lack of nutrition is a pretty good bet. Here’s how to fix yellow rhododendrons (and azaleas and pieris, too) and get them back on the green and into the hole in four strokes.
If you’re a fan of rhododendrons, you know how incredibly beautiful their foliage and blooms can be. This holds true for azaleas – which are rhododendrons – and Japanese pieris, which are close relatives of rhodies. Their exotic-looking blooms and glossy green foliage make all of these plants real attention grabbers in any garden or landscaping scheme. But if you grow these plants in your own garden, there’s a decent chance you may have encountered a fairly common problem to which they’re all susceptible: yellowing, or chlorotic, foliage.
I have experienced this problem in the past with my rhododendrons, and have dealt with it successfully. I’m also currently dealing with yellowing rhodie foliage as a result of a sort of “wild card” situation (I’ll explain a bit later).
Although yellowing rhododendron, azalea, or pieris foliage can arise as a result of a number of different conditions and problems (for example, parasite/insect infestations, root infection/trauma/damage, overexposure to direct sunlight, etc), the most common causes – at least in my garden – are a higher-than-acceptable soil pH and a lack of nutrition. And the former generally begets the latter.
So here’s the lowdown for today: I’m going to tell you how rhododendron, azalea, and pieris plants are related to each other, and why proper soil pH is so critical to them. And them I’m going to show you how I eliminate and prevent yellowing foliage for these guys in my garden. And finally, I’ll tell you the “wild card” story of one of my very unlucky rhodies, and why my methodology may not be enough to save it.
All in the Family
Rhododendrons and azaleas. Rhododendrons, azaleas, and pieris all belong to a family of plants known as Ericaceae. Rhododendrons and azaleas both belong to the genus Rhododendron. This genus is broken down into approximately one-thousand species, further organized within various subgenera. The bottom line is that all azaleas are rhododendrons, but not all rhododendrons are azaleas. In my garden, all of my rhododendrons are evergreen, while my lone azalea is deciduous. There are differences in bloom structure and appearance, as well. For example, rhodies generally have bell-shaped flowers with at least ten stamens per bloom lobe, while azaleas have tube-shaped blooms with five stamens per lobe. There are a number of more specific, esoteric differences between rhodies and azaleas which I’m not going into here. For an excellent overview of the genus Rhododendron, and its subgenera and species, please visit The American Rhododendron Society’s website. For the purposes of this article, I’ll use the colloquial names respectively assigned to each of these plants by growers and nurseries: rhododendrons and azaleas. If you bought a rhododendron from a nursery, it’s a rhododendron. If you bought an azalea, it’s an azalea.
Pieris. The Japanese pieris (or Japanese andromeda, as it’s also known) belongs to the genus Pieris and is of the species P. japonica. It is in the same Ericaceae family as rhodies and azaleas, and resembles them in terms of basic form and foliage. The pieris’ flowesr, however, differ dramatically from those of rhodies and azaleas, in both appearance and anatomy. I’ve currently got one Japanese pieris growing in my garden.
One thing that all of these plants undeniably have in common is their need for acidic soil. 6.0 on the pH scale is good, but 5.5 is better. These plants absolutely need this level of acidity in order for them to properly absorb nutrients from the soil. If the pH level of the soil in which they’re planted is too high, they simply will not be able to absorb the nutrients they need for survival and growth. And another critical commonality among these plants is the obvious need for said nutrients. They do need the usual triumverate of N-P-K (nitrogen, phosphorous, and potassium), but they also need iron. In fact, it’s a deficiency of iron which typically manifests itself in the form of yellowed, or chlorotic, foliage. A yellow rhodie, azalea, or pieris is, most often, crying out for nutrients, and it’s crying out for acidic soil so it can absorb those nutrients. It needs nitrogen, phosphorous, and potassium. It needs iron. And it needs acid.
How to Fix Yellow Rhododendrons, Azaleas, and Pieris in Four Steps
Step One: Check Your Soil
Before you do anything else, check the pH level of the dirt that houses your chlorotic rhodies, et al. You’ll need to know this in order to proceed with a rescue plan. If the pH level is substantially above 6.0, there’s an excellent chance that the soil isn’t acidic enough to allow your Ericaceae family members to access nutrients which (hopefully) are already at least partially present right there in the ground. If your yellow rhodies’ soil has a pH level between 5.0 and 6.0 (which is a good range), you’ll need to check its nutrient content. A good start is to check the soil’s N-P-K levels. A deficiency of nitrogen, phosphorous, and/or potassium could definitely lead to serious health issues for rhodies, azaleas, and pieris, and can contribute (at least partially) to the chlorotic foliage problem in all of these plants. And a deficiency of iron will for sure, beyond any shadow of doubt, turn these guys yellow – it’s the primary contributing cause. I use a Luster Leaf Rapitest 4-way soil analysis meter to measure my soil’s pH and N-P-K content. This meter is incredibly useful in helping me to quickly get a handle on what’s happening with the soil in my garden. This particular meter doesn’t check for iron levels in the soil (I don’t know of any commercial metering products which do, but I haven’t looked too terribly hard). But remember, a lack of iron is the most significant contributing cause of chlorosis. My motto for rhodies, azaleas, and pieris: They can never have too much iron. And if your plants’ soil has acceptable acidity and N-P-K levels, there’s an excellent chance (barring some of the extraneous causes I mentioned earlier – parasites, disease, damage, etc) that an iron deficiency is the culprit.
Knowing how to fix yellow rhododendrons starts with knowing their soil. I bought this Luster Leaf Rapitest 4-way soil analysis meter in February of 2022 and have used it successfully time after time since then to test for soil fertility and pH levels. It also measures sunlight and soil moisture levels. It’s fast, easy to use, convenient, and accurate. By using this device, I’ve been able to determine the necessity of appropriate fertilizer applications and pH amending to the soil of a large number of the plants in my garden. Order it here, directly from Amazon, by clicking the #advertisement link. Note that this unit doesn’t test for iron levels in soil. Also note that I really love this little meter!
In the case of the soil in my garden, it’s uniformly slightly acidic, with a few areas of notable exception. In the few spots where I’ve got plants growing which do well in alkaline soil, I’ve amended the ground with garden lime to increase the soil’s pH. You’re going to learn about the other notable exception to my garden soil’s general slight acidity a bit later in this article (I can tell you now that this is a problem spot, and it’s got a rhododendron planted squarely in the middle of it). In my existing, only-slightly-acidic garden soil (the above two exceptions notwithstanding), my rhodies, azalea, and pieris would do okay, assuming I provided them with the proper nutrition. Not great. Just ok. Remember, these are all acid-loving plants.
Which brings me to step number two…
Step Two: Send Your Rhodies, Azaleas, and Pieris on an Acid Trip
Since my garden’s slightly acidic soil is not acidic enough for my rhodies and company, I acidify it. I do this for the first time in spring (which, in the case of most of my rhodies, my azalea, and my pieris, is enough) and then again in 60-day intervals, only if necessary, to maintain/increase acidity levels and decrease pH levels. The product I use to acidify my garden’s soil is Espoma Soil Acidifier. It’s an organic product that’s really simple to use and incredibly effective. Because my planting beds are mulched with wood chips, my first move when acidifying a particular plant’s soil is to clear the mulch from beneath each plant out to just past its drip line, in order to expose the soil. I then lightly rake the soil with my fingers and top dress it with the product per Espoma’s directions. Then I heavily water it in. This product is so effective at lowering pH levels in my garden’s soil, that one application is generally enough to reach and maintain proper pH levels for the entire active growing season. Its primary acidifying agent is sulfur, which it has in abundance (a combined amount of 30% from elemental sulfur and gypsum).
Espoma Organic Soil Acidifier is the perfect product for lowering the pH and increasing the acidity of your garden’s soil. It’s a fabulous organic product which I’ve used to lower soil pH for plants like my blue hydrangeas and my rhododendrons, azalea, and pieris. It’s very effective and allows acid-loving plants like these to properly access and utilize nutrients from fertilizing products. Order it here, from Amazon, by clicking the #advertisement link.
As I’ve already mentioned, for most of my rhodies, and for my azalea and pieris, one Espoma Soil Acidifier treatment in spring is good for the whole year. But your own soil conditions may dictate additional applications. In any event, within a week of application of Espoma’s Soil Acidifier, my soil is achieving and maintaining a rhodie-friendly soil pH of approximately 5.5 in the immediate vicinity of each target plant. This level of acidity means that nutrients from the soil are now accessible to each plant.
Now, I hope you didn’t re-cover the dirt under your plants with the mulch you just moved, because we’re about to add some fertilizer…
Step Three: Fertilize
After I add soil acidifier to each plant’s soil, I leave the soil uncovered and wait a week to add a granular fertilizer. And the fertilizer I use is Espoma’s excellent Holly-tone. It’s a fabulous organic product with an N-P-K of 4-3-4, six million colony forming units of beneficial microbes, and a sulfur content (yep, it’s got its own soil acidifying capabilities built right in) of 5 percent. It’s just about perfect for acid loving plants like rhododendrons, azaleas, and pieris. I apply it to the still-exposed soil around each target plant approximately one week after I apply the soil acidifier, and I heavily water it in. I wait a week to apply it because I’m concerned about possibly shocking/overwhelming the plants’ root systems. Also, by waiting a week, I’ve allowed the soil acidifier to substantially effect the necessary change in soil pH which allows for the uptake of the nutrients in the Holly-tone by the plants. Espoma recommends one feeding in spring, and a second, lighter feeding in the fall.
And now’s the perfect time to re-cover the treated soil with the mulch we moved out of the way during Step Two. It won’t be in the way for Step Four.
Espoma Organic Holly-tone is the almost perfect fertilizer for acid-loving plants like rhodies, azaleas, and pieris. It’s an organic formulation with an N-P-K of 4-3-4, a multitude of beneficial microbes, and a respectable amount of sulfur (5%) on tap for performing its own bit of soil acidifying. Like I said, it’s almost perfect. And when it’s used in conjunction with the fertilizing product in the next step, it is perfect. Click the #advertisement link to conveniently order it here, from Amazon.
Espoma holly-Tone is such an excellent product for providing my rhodies and company with the necessary nutritional base for developing and maintaining healthy and strong root systems and aerial structures. It’s got great N-P-K, it’s got it’s own acidifying component, and it’s got beneficial microbes. As I mentioned earlier, it’s just about perfect. The only nutrient essential to rhodies, azaleas, and pieris that this product doesn’t provide is iron. And I’m getting to that…
Step Four: Add Iron in Liquid Form
The final step in the process I use to keep my Ericaceae family members glossy, green, and healthy involves the addition of iron to their diets. When plants have access to absorbable iron, they simply do not become chlorotic (assuming the absence of extenuating circumstances). Iron is used by plants for, among a multitude of other things, the production of chlorophyll. When plants can’t produce chlorophyll, they become chlorotic. Yellow. (For an in-depth analysis of iron’s importance to the health of plants, please click here.) So rhodies and company definitely need iron. And there are a number of available methods for getting it to them. Application of items like granular blood meal and manure to the target plant’s soil will definitely deliver accessible iron to that plant. But I prefer a product which I consider easier to use and more immediately effective at providing the plant with usable iron than blood meal or manure.
Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron provides a remarkably effective means of delivering all-important iron to rhododendrons, azaleas, and pieris. This liquid product is made from Ascophyllum nodosum seaweed harvested in the waters off the coastline of Norway. It’s got an N-P-K of 0-0-1, and has an iron content of 2 percent derived from the seaweed and from ferrous sulfate. This product is applied as a root and foliar drench. Both the roots and foliage of the target plant quickly absorb the iron and other nutrients in this product.
My first application of this product comes a week after my application of the Espoma Holly-tone. Although the two products work beautifully together, I do like to wait that one week after the Holly-tone goes down before I apply the Maxicrop. I mix this product with water in a 2-gallon watering can per the manufacturer’s directions and apply it liberally over each plant’s foliage and roots. The manufacturer suggests a weekly application. My azalea seems to benefit from a feeding once every two or three weeks, but my rhodies and pieris get a shot every week. The effects of this product (when used according to my four step process) are almost immediately evident. Treated plants appear glossier and greener the day after being fed this product. No joke. It’s that effective when used according to the four step procedure I’ve outlined here. I wait two days after I apply the Maxicrop to water heavily. That gives the plants plenty of time to absorb the iron at both the root and foliar levels.
A note of caution: Be careful when mixing and applying this stuff. It will definitely stain wood and concrete surfaces.
Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron is a remarkable source of iron for acid loving plants. When used in conjunction with the other products referenced here in this four step process, it literally works miracles. It’s got an N-P-K of 0-0-1 and it contains 2% iron. It’s sourced from Ascophyllum nodosum seaweed harvested from the waters along Norway’s coastline. The beneficial effects of this product are noticeable almost immediately after its application. Order it here, from Amazon, by clicking the #advertisement link.
The Gameplan in Review
Rhododendrons, azaleas, and pieris, all members of the family Ericaceae, are acid-lovers. They need acidic soil in order to access and process nutrients. Nitrogen, phosphorous, and potassium are obviously of critical importance to these plants. But iron is definitely the key to keeping these plants from turning yellow (becoming chlorotic). When they’re growing in acidic soil, rhodies, azaleas, and pieris can really soak up these nutrients and grow and flower beautifully while remaining as green as cash. So what do you do to ensure all of this?
- Test your soil. Find out what all your numbers are (pH and N-P-K).
- Acidify your soil if it’s pH is much above 6.0. I use Espoma Soil Acidifier to accomplish this. When the soil’s pH is between 5.0 and 6.0, your rhodies, azaleas, and pieris can really soak up the nutrition that you’re about to serve them.
- Fertilize with a product that provides a beneficial combination of N-P-K. Espoma Holly-tone not only does that, it delivers a huge dose of beneficial microbial action, and helps acidify the soil with its sulfur content. It’s a nearly perfect granular organic fertilizer.
- Add iron in the form of Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron. It’s a miraculous root and foliar drench that gets results fast. It delivers that all-important iron dose which prevents yellowing foliage. When fed this product, rhodies, azaleas, and pieris literally green up and grow overnight.
Do all of these things, and you’ll love your glossy green rhodies, azaleas, and pieris. And I’m pretty sure they’ll love you back.
Knowing how to fix yellow rhododendrons (and azaleas and pieris) also implies knowing what to use and when to use it. My rhodies, azalea, and pieris benefit from wintertime applications of Espoma Organic Soil Acidifier (see the three photos below).
My Unfortunate Polar Night Rhododendron
Early in this article, I mentioned that there were other factors beyond high soil pH and poor nutrition which could lead to chlorosis in rhododendrons, azaleas, and pieris. The little plant I’m about to tell you about is a victim of such circumstances. It’s currently fighting for its life. And I’m fighting for its life, as well.
If you’re a regular reader of, or a subscriber to, this site, you will know of this plant from its encounter, nearly two years ago, with Larry the mole. In short, a mole – Larry – excavated and inhabited a den directly under the root system of this plant in the late summer of 2020. The plant became yellow but survived the winter. I discovered the den in the spring of 2021, ultimately evicted Larry from the garden shortly after that, and replenished the soil beneath the plant’s roots with well-acidified, well-fertilized soil. The plant recovered beautifully and flowered profusely. It remained healthy and green until early August of 2021, when it once again began to exhibit signs of chlorosis.
The rhodie made it through the winter, but entered spring looking yellow and unhealthy. Several weeks ago, I evaluated and categorized this plant’s two primary problems. They are as follows:
- The plant was unfortunately bedded right in the middle of a discharge point for my property’s septic system. This system utilizes not only standard leech pipes which allow septic wastewater to gently seep out into the soil of the septic field (located mostly outside of the boundaries of my garden), it also uses a distribution box system which employs a powerful ejector pump to forcefully move the wastewater out to other distribution points. This rhododendron happens to be planted directly within the boundaries of one of these distribution points. The water supplied to our home is well water. Despite the fact that a water softener system treats the water we use in our home, this water remains alkaline, or “hard.” This is the water which ultimately ends up in the septic tank as wastewater, and is frequently discharged into the soil in which the rhododendron in question is growing. The already alkaline water becomes even more so after it sits in the septic tank with all of the other crap (bacteria, household chemical waste, and, well, crap) that resides there. This alkaline cocktail is what informs this particular rhododendron’s soil on a fairly regular basis. So keeping the soil in this specific location acidic enough for the little rhodie is difficult. Difficult, but not impossible. Over the course of spring, summer, and fall I’m able to keep this rhodie’s soil pH below 6.0. The soil is at its most alkaline in early spring (immediately before I first treat it with acidifier) after a winter’s worth of alkaline discharge (you can’t apply soil acidifier in the winter). But soon, the soil will be ready for a second application of acidifier, which should be enough to drop the pH below 6.0. That will be a big help in the fight to save this plant’s life.
- This little rhododendron faces a bigger problem than slightly elevated soil pH. Last summer, my garden suffered a massive vole infestation. By late autumn, I’d mostly driven the voles out of my garden. But it wasn’t until this spring that I was able to fully comprehend the entire range of damage they’d caused the year before. One of the victims of my pernicious erstwhile vole population was this little rhododendron. In early spring, I’d decided to replace much of the existing soil (turned alkaline by a winter’s worth of septic discharge) around and beneath it’s roots with freshly acidified new soil. When I began gently excavating around the root crown and roots of this plant, I discovered that voles had destroyed a sizable portion of the rhodie’s root system and even a portion of the root crown itself. This little plant is living with some pretty substantial structural damage to its root system, which obviously interferes with its ability to take up moisture and nutrients. So although I’ve got the soil pH pretty close to where it needs to be, the plant’s compromised root structures are hindering its ability to derive nutrients from the soil.
The best I can do with this little guy is keep him dialed into my four step process. I’ve been at it for several weeks. It’s gotten an initial dose of soil acidifier (and will soon receive another), it’s been fed with Espoma Holly-tone, and it’s received a few drenchings of Maxicrop Liquid Seaweed Plus Iron. Has it improved? You be the judge. The photo below shows the rhodie from approximately four weeks ago (on the left), and from a few days ago, on the right. It may just be wishful thinking, but to me, it looks like it’s now a little greener. Keep your fingers crossed.
If this rhododendron survives and flourishes on its current regimen, I may end up drenching myself with liquid seaweed.
Cheers, and Happy Gardening!
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This is very informative- thank you.
I’m going to try the 4 step process.
One question please- should I remove the yellow leaves? I’m assuming so – but thought I’d ask.
Appreciate your help in advance.
Best.
Elizabeth
Thank you so much for reading the article, Elizabeth. I’m so glad that you’ve found it to be informative. This process has worked beautifully for me for years. Since the water that I use to irrigate my garden is very alkaline (it’s well water), it’s a constant battle for me to maintain acidic pH levels. By keeping that soil in the acidic range, I’m able to provide my rhodies, et al with nutrients they can effectively assimilate. To answer your question about removing yellow leaves, I’m going to equivocate. If those yellow leaves are actually more brown than yellow, and/or definitely shriveled and brown/dead, than my answer would be yes. Remove them in that case. If the leaves are yellow (or yellow-ish), but the veins on each leaf are still definitely green, do not remove them. The liquid seaweed product delivers iron to the plant through a root AND foliar drench. In other words, when the liquid seaweed product is applied, you’ll not only water it in to the soil, you’ll sprinkle it all over your plants’ yellow leaves (as long as their veins are definitely green) so those leaves can also absorb the iron in the product. I hope this answer is helpful. Thank you once again for reading the article, Elizabeth, and for commenting here. I really appreciate it. Please do reach out and let me know how the rejuvenation process is coming along. I wish you the very best of luck.
Good morning! Good information here. It’s wonderful how well you take care of your plants. Take care.
Thank you, Kelly. I appreciate that. I’m glad you liked the article. I try to make sure that the plants all stay as healthy as possible. When they’re healthy, they’re also happy. And then I’m happy. It’s really a great feeling for me when I know that my actions are helping these living things thrive. Thanks again!
Your rhododendron is getting greener. I know you will bring it back to good health. Tons of great information as always. I love rhododendrons and they live a long time. Thanks for helping us keep them healthy.
Thanks for the vote of confidence, Kevin. I’m definitely pulling out all the stops to save that little guy. And I agree. Rhodies are such beautiful bushes. It’s wonderful that, if we’re lucky, we can keep them in our lives for a long, long time. Thanks again, Kevin.
Perfect timing for this educational article. I have fertilize plants on my vacation to do list this week. Now I’ve added: test, acidify, (fertilize), add iron. Thanks! And my fingers are crossed for your little rhodie!
Thank you so much, Jill. I’m so glad the info was useful. Your garden is already so incredibly beautiful, I’m thrilled that you found my humble offering helpful! And I appreciate the kind wishes for my poor little rhodie. It’s been through so much over the last two years. I’ll be seriously upset if it doesn’t pull through. I’m sure that your positive vibes and kind thoughts will really help – thanks again!
Gardeners are the eternal optimists otherwise we’d quit gardening. Weather, varmints, soil and everything else seems overwhelming. Yet, we continue. My husband’s great-grandfather used to haul water from a creek, up to his garden in a bucket. The poor rocky soil grew food to feed his family. His daughter said in the evening when he sat down, he was shaking.
Wonder what the old-timers used? Manure mainly. I used to use a liquid chelated iron on my citrus trees but I’ve since lost the bottle. Wonder if your iron could replace it?
Thank you for sharing your thoughts and the story of your husband’s great-grandfather, Everly. I can only imagine how hard he must’ve had to work in order to provide for his family. I firmly believe that the triumphs of today are firmly built upon the toil of the past. We owe our ancestors a great deal. The liquid iron product has proven incredibly effective for my various Ericaceae bushes. The combination of appropriate soil pH, plenty of N-P-K, and the iron has worked wonders. I’m curious to know if higher soil acidity is required in order for such plants to absorb the iron at the foliar level when the leaves are drenched. In any case, I don’t think the manufacturer of the liquid iron product recommends its application to edible crops. But if you’re not eating the fruit, it may not be an issue. In any case, the product is working extremely well for me. As always, Everly, I’m truly grateful for your thoughts and your interest. Thanks once again.
I forgot the rest of the story. His great-grandfather lived to be 97 years old.
Wow! Proof positive that hard work never hurt anyone. Sounds like an amazing man. Thanks again for introducing us to this incredible man.
Thanks John, a beautiful garden is a lot of work & knowhow, which I think is the reward in itself.
Thank you so much for your thoughts and your very kind compliment, Tess. I entirely agree with your take on the hard work and effort. It really is, at least for me, a reward in itself. Makes the successes in the garden even sweeter. Thanks again, Tess. As always, your thoughts and interest are truly appreciated.
This is very helpful information.
Thank you. Glad you found the info useful. It’s definitely a good thing to be able to fix this problem. These are such beautiful bushes, they really do deserve to look their best.
Very informative and helpful!
Thank you, Nykki. I’ve always learned by making mistakes – sometimes big ones – and fixing them. This article is the kind of thing that I think would’ve been helpful when I first planted rhododendrons in my garden. Thanks again.
Such amazing knowledge !
Very well written and so much information, the images are beautiful. You have such a way to write and describe in depth it’s amazing 🙏💕🌸
Thank you so much, Roxxy – I really appreciate that! My goal, with articles like this one, is to help readers avoid the kinds of (numerous) mistakes I used to make when I first started gardening. Believe me, I still make mistakes. Just not quite as many as I used to! Thanks again for all of your kind interest and wonderful support of my efforts. It’s all truly appreciated.