Rhododendrons are among the blooming stars of spring and early summer. They are woodland shrubs that create an array of colorful flowers in the garden.
The best fertilizer for rhododendrons is usually needed when the soil has become deficient in nutrients. Otherwise, these acid-loving flowers can be left on their own.
Aged manure and compost are usually enough to nourish the soil with nutrients. However, with a heavy deficiency in nutrients, several plant foods for rhododendrons, azaleas, and other acid-loving flowering plants are a must. The usual NPK ratio usually has a greater rate for phosphorus than nitrogen and potassium content.
Newly mulched rhododendrons using sawdust and woodchips may also experience nitrogen deficiency. The decomposition of these organic matter will take up the nitrogen in the soil, stealing it from your flowering plants. It will cause stunted growth and foliage problems if left untreated.
If nitrogen deficiency is your only problem, you can get it from natural sources like bone meal or feather meal. If the soil is at a good soil pH level, you may also use a general fertilizer with an NPK ratio of 10-10-10.
In this post, we will share several brands of fertilizers for rhododendrons based on the nutrients that they lack to produce beautiful blooms and lush green leaves.
10 Best Fertilizer For Rhododendrons in 2022 [Top Picks & Reviews]
We listed several nitrogen-based fertilizers and specialized fertilizers for acid-loving plants.
The three numbers that you see in fertilizer is the NPK ratio and looks like 10-10-10. It stands for nitrogen, phosphorus, and potassium content of fertilizers, respectively.
Now, let’s get on to your fertilizer options.
1. Jobe’s Organics Fertilizer
Let’s begin our list with the organic goodness of Jobe’s Organics Azalea, Camellia, and Rhododendron Fertilizer. It is a granular fertilizer with an NPK ratio of 5-4-3. As an organic fertilizer, it contains natural ingredients, such as:
- Feather meal
- Bone meal
- Processed poultry manure
- Sulfate of potash
This fertilizer is designed for acid-loving flowering plants. It does not contain any lime or any soil acidifier so it won’t risk changing the soil pH level. Its manufacturer prides itself on not using any synthetic chemicals and is certified by OMRI as organic.
Other nutrients in this fertilizer are as follows:
- Calcium (7.0%)
- Magnesium (0.5%)
- Sulfur (1%)
The best features of this fertilizer are its organic formulation and containing healthy soil microbes to help break down natural materials for the plant’s consumption.
It is also fortified with Biozome technology to improve soil health and increase the resistance of your rhodies to pests, drought, and stress.
2. Dr. Earth Organic 4 Azalea/Camellia/Rhododendron Acid Fertilizer
If you’re a conscious organic gardener that aims to get the cleanest fertilizer in the market, Dr. Earth Acid Lovers is the one for you. It uses food-grade organic materials that are free from any animal manure. The brand aims to provide the best quality of natural nutrients to acid-loving plants.
It is derived from:
- Clean cottonseed meal
- Alaskan fish bone meal
- Valley-grown alfalfa meal
- High-country feather meal
- Naturally-mined potassium sulfate
- Norwegian cold-water kelp meal
- Concentrated seaweed extract
This fertilizer has an NPK ratio of 4-5-4. Unlike other fertilizers, it can make the soil more acidic, so monitor the soil pH level and apply this to your rhodies.
It is enriched with TruBiotic formula that contains a healthy soil microbiome to speed up the breakdown of natural ingredients and make them readily available for your plants.
The best thing about this fertilizer is you can be sure about the cleanliness of the ingredients. It is safe to use around kids and pets and does not leak into the groundwater and compromise the safety of marine animals. It is by far the best one among the organic fertilizers when it comes to quality.
3. Jobe’s Azalea, Camellia & Rhododendron Fertilizer Spikes
If you’ve recently mulched your Rhodies and other acid-loving plants, you might want to continuously feed them with nitrogen to replenish the nutrients in the soil. The decomposition of wood chips and sawdust as mulch consumes the nitrogen in the soil and steals it from your plants.
Jobe’s Organics Fertilizer Spikes for Azaleas and Rhododendrons are the best option to ensure that your Rhodies are continuously getting nutrients during the growing season.
This fertilizer spike has an NPK ratio of 9-8-7. It is designed to slowly release nutrients into the soil during watering. It is ideal for senior gardeners and those with physical disabilities since it lessens the burden of measuring and mixing fertilizers. The spikes are derived from:
- Ammonium sulfate
- Ammonium phosphate
- Potassium chloride
Aside from maintaining nitrogen in mulched soil, Jobe’s fertilizer spikes help nutrient deficiencies that cause the leaves to turn yellow.
Gardeners see new green growth in their rhodies upon using these fertilizer spikes. Plus, one spike can last for several months of feeding.
4. Espoma Holly Tone
Espoma Holly Tone is a popular fertilizer among organic gardeners. It is a 4-3-4 NPK fertilizer enriched with Bio-Tone formula to improve soil condition.
If you are looking for a more affordable organic fertilizer, this is a must-try. It’s best used for the following plant varieties:
- Bleeding Heart
- Mountain Ash
- Mountain Laurel
Use this fertilizer for blooming evergreens like azaleas and rhododendron in spring when they start to bloom. Most gardeners notice that their rhodies and acid-loving plants start to look healthier and fuller two weeks after using Espoma.
It is derived from:
- Feather meal
- Poultry manure
- Bone meal
- Alfalfa meal
- Sulfate of potash
- Sulfate of potash magnesia
- Elemental sulfur
The best feature of this fertilizer is its price point. Most gardeners can also attest that it is fast-acting. It is also used to help revive struggling rhododendrons and azaleas. It is also packed with extra nutrients which include:
- Calcium (5%)
- Magnesium (1%)
- Sulfur (5%)
- Humic acids (1%)
Since it is an organic fertilizer, it has a stinky smell that dissipates in the air in the long run. However, dogs are so attracted to it.
So, you may need to spend some effort in keeping them away from your plants after application.
5. Miracle-Gro Water Soluble Azalea, Camellia, Rhododendron Plant Food
If you don’t mind using synthetic fertilizers, Miracle-Gro Fertilizer for acid-loving plants can be enough to perk up the blooms of your rhododendrons. It is formerly known as Miracid.
It is 30-10-10 NPK fertilizer derived from the following materials:
- Ammonium phosphate
- Potassium phosphate
- Potassium chloride
- Boric acid (0.02%)
- Copper (0.07%)
- Iron (0.325%)
- Manganese (0.05%)
- Sodium molybdate (0.0005%)
- Zinc (0.07%)
This fertilizer is the blue granules that you often see online. It has a water-soluble formula that helps speed up the nutrient uptake of acid-loving plants. You may use it for the following varieties of plants:
Most gardeners love this fertilizer due to its fast-acting effect on rhododendrons. The blooms and foliage that it produces are bright in color and grow abundantly.
Plus, its formula contains extra nutrients like iron that are essential in healthy plant systems.
6. Schultz Water Soluble Plant Food
Another synthetic fertilizer that is unknown to some gardeners is Schultz Water-Soluble Plant Food for acid-loving plants.
It is a 32-10-10 NPK fertilizer that is dissolved in water for the fast absorption of nutrients of rhododendrons, azaleas, and other acid-loving plants. You may use it on both indoor and outdoor plants.
Unlike organic fertilizers, it doesn’t have the distinct organic smell that can make your indoors stink.
So, if you’re looking for something tolerable but still effective, this fertilizer is a good option for you. There’s not enough information about its contents but it’s certainly not organic.
Most gardeners love it for its fast-acting formula. It is also enriched with extra micronutrients and increased nitrogen content for improved foliage growth and bloom production.
The only concern that you may encounter with this fertilizer is the handling risks if you have kids and pets that may play or eat it.
7. Down to Earth Blood Meal Fertilizer Mix 12-0-0, 5 lb
There are two reasons why nitrogen fertilizers are also needed in nourishing rhododendrons.
First, nitrogen fertilizers help lower the soil pH levels which means they make it more acidic. They also replenish the lost nutrients in the soil due to the decomposition of wood-based mulch. A blood meal is one of the natural sources of nitrogen that you can use.
Down to Earth Blood Meal Fertilizer is an organic source of nitrogen for plants that has an NPK ratio of 12-0-0. It is OMRI-listed and a versatile soil amendment.
Aside from feeding rhodies, it can also be used to speed up decompositions and heat compost piles. You may also use it to help jumpstart foliage development in other plants like fruit and vegetable varieties.
Many gardeners benefit from using blood meal since it is versatile and has a lot of uses. In some cases, gardeners also use it as a rabbit repellent. However, be sure to check the amount that you will add to your soil since too much blood meal can burn your plants.
The only concern for this brand is its packaging. Since the manufacturer focuses on the product for being environment-friendly they opt to use a box rather than a resealable one.
Due to its content, dogs and flies may also be interested in it.
8. Fish Meal by Power Grow Systems 8-6-0 (5 lbs)
Another good source of nitrogen for rhododendrons is fish meal.
If you are looking for an affordable fish meal that can provide value for your money, you should try Fish Meal by Power Grow Systems. It is an 8-6-0 NPK fertilizer that aims to improve foliar growth and bloom production in plants.
Fish meal is a common organic ingredient in most fertilizers that helps stimulate soil microbes. This fish meal, in particular, contains 5% calcium which helps improve the quality of plant cells for better nutrient distribution. Though this brand is not part of the mainstream categories, it is among the effective ones in the market.
Since it is derived from fish materials, it has a distinct odor. However, as soon as you mix it with other soil amendments, the smell will eventually dissipate. It is also safe for kids and pets that may be loitering around your garden.
9. Down to Earth Organic Fish Meal Fertilizer 8-6-0, 5 lb.
Another variety of fish meals for you to choose from is the Down to Earth Organic Fish Meal.
It has an 8-6-0 NPK ratio which helps promote healthy foliage growth and bloom production. The manufacturer prides itself in formulating fertilizers that do not contain any synthetic materials, growth stimulants, and low-quality fillers.
You may use this fish meal to jumpstart the development of your rhododendrons, vegetable plants, flower beds, trees, and shrubs.
Many gardeners see how their azaleas and rhodies started to perk up and bloom non-stop upon using this fish meal. They also use it as an alternative to fish emulsion due to its fast-acting effect on their plants with a less stinky smell.
The only problem with most organic products like this fish meal is its smell. Some gardeners find their dogs snacking on this fertilizer.
So, if you have persistent dogs around, you may want to keep them off the garden upon application or store this fish meal in a cabinet where they can’t reach it.
10. Ferti-Lome Azalea, Camellia, Rhododendron Food 9-15-13
Ferti-Lome Azalea, Camellia, Rhododendron Food is one of the most underrated fertilizers for acid-loving plants. The brand has been around for years, but many new gardeners are not aware of its magic.
It is a 9-15-13 NPK fertilizer that helps increase the acidity of the soil for improved nutrient absorption.
This fertilizer is enriched with vital trace elements to build up an acidic environment for rhododendrons. It is a synthetic fertilizer that is derived from the following materials:
- Ammonium sulfate
- Ammonium phosphate
- Muriate of potash
- Boron (0.02%)
- Copper (0.05%)
- Iron (0.10%)
- Manganese (0.05%)
- Zinc (0.05%)
Most gardeners who discovered the amazing benefits of Fertilome fertilizers have never tried other brands again.
Though it’s a synthetic fertilizer, it has been good nourishment for rhododendrons and azaleas that are starting to lose leaves, have yellowing leaves, and stopped blooming for many years.
See it for yourself by trying out this sought-after product that is no longer available in most local garden stores.
Things To Know In Fertilizing Rhododendrons
When it comes to fertilization, anything that’s too much can also kill your rhododendrons.
In a gardener’s term, too much love for your plant through feeding can do more harm than good. Acid-loving plants planted in fertile soil should be left alone on their own.
However, there are instances wherein fertilization is needed to ensure that your garden will be covered in blooms during the spring season.
Here are some of the things to remember in fertilizing rhododendrons:
Rhododendrons mulched with wood chips and sawdust will need regular nitrogen feeding. The decomposition of wood matter in the soil takes up so much nitrogen in the soil which robs off the nutrients for your plants.
Check the soil acidity of rhododendrons before you apply specialized fertilizers for acid-loving plants. They are designed to lower the soil pH to increase the nutrient uptake of plants.
When the soil pH does not match the acidity needed by plants, the roots will find it hard to absorb the nutrients in the soil. You may use a soil pH meter to monitor the acidity before you apply fertilizers.
There are several possible reasons why leaves of rhododendrons turn yellow. Yellow spots between the veins of leaves indicate a magnesium deficiency. You can treat this by applying Epsom salt to the soil.
In some cases, yellow leaves also indicate nitrogen deficiency. It usually occurs when the soil has been mulched. To replenish the lost nutrients, you can count compost and aged manure. You may also use nitrogen fertilizers like blood meal and fish meal.
Organic Fertilizer vs. Synthetic Fertilizers
Organic plant food takes time to release nutrients into the soil. It is the reason why some organic brands are adding beneficial bacteria in their fertilizers to speed up the breakdown of nutrients.
Chemical fertilizers are usually absorbed easily by the plants. So, they require frequent applications.
Best Growing Conditions For Rhododendrons
Rhododendrons and azaleas have blooms that outshine other flowers during the spring season. Their leaves can remain deep green through winter.
If you fell in love with the beautiful blooms of these two acid-loving plants, here are the best growing conditions that you need to prepare for your Rhodies and Azaleas:
Rhodies and azaleas have shallow roots. So, they may experience drought stress easily when under direct sun or during hot temperatures. They usually thrive in partially-shaded areas with morning sunlight. However, the amount of sunlight and shade depends on the climate in the region.
- Tropical regions: Full shade
- Warm and humid region (Zones 7 to 11): Partial shade where they can get the afternoon sun
- Cold or temperate region (Zones 3 to 6): Full sun
Type of Soil
Rhododendrons need acidic soil with a soil pH of 4.5 to 6. It should also be well-draining and moist to prevent the topsoil from getting too dry.
You may also add compost to improve the soil quality and enrich it with complete nutrients. If it’s too hot in your region, mulching them for 2 to 5 inches could also help retain the moisture.
Water your Rhodies with 1-inch of water per week if there’s no rain.
Rhododendrons are not an exception for hungry little crawlers. You may use a dish soap solution to get rid of the following pests:
- Vine weevil
- Scale insects
- Powdery mildew
- Bud blast
- Leafy gall
- Petal blight
Frequently Asked Questions (FAQs)
Do rhododendrons come back every year?
Yes. They go through winter and may look dead but they will bloom back during Spring.
Most gardeners are worried about how their rhododendrons look as the cold season comes like yellowing and falling leaves. However, they are perennial plants and usually take some hibernation as they wait for the spring season.
Do rhododendrons like sun or shade?
Rhododendrons can endure the full sun in cold regions. However, due to their shallow roots, they may easily become sensitive to drought in hot regions.
So, they could use some morning or afternoon sunshine but with shade for the rest of the day. In tropical areas, they can survive in shaded areas.
What time of year do rhododendrons bloom?
Most varieties of rhododendrons bloom during springtime. However, several varieties bloom in other seasons of the year. Early-season varieties usually bloom between December to March or April to early May.
The bloom production may last for 2 months to 7 months depending on the variety of rhododendrons that you are growing.
We hope that this post has been an eye-opener to novice gardeners about the different fertilizers that they can try.
Rhododendrons are not sensitive when it comes to their plant food. However, they may tend to be more overwhelmed with too many fertilizers than being a heavy-feeder.
If your Rhodies are doing just fine and bloom every year, they can already appreciate more compost than a full-blown fertilizer.
For our top picks from our list, we chose Jobe’s Organics as an eco-friendly and reliable plant food for rhododendrons. Many gardeners trust the brand and have been patronizing it for its value for money.
Our second pick is Dr. Earth for its clean and premium-quality fertilizers. Last but not the least, we chose Fish Meal by Power Grow Systems for being one of the most underrated but highly efficient brands in the market.
Every fertilizer has its pros and cons and some of them are selected due to their ability to help revive malnourished Rhodies and push them beyond their limit when it comes to their bloom production.
If you find this post helpful, please don’t forget to share it with your friends. Also, share with us your experience in the comments section below. May you enjoy the new blooms of your Rhodies in the next spring through any of the fertilizers we listed here.