Horticulturalists the World over are familiar with the glossy foliage and spectacular blooms of the impressive evergreen that is Gardenia. With more than 200 varieties, they come in a wide range of shapes and sizes, providing structure and definition to gardening landscapes throughout the seasons.
Unfortunately, and all too often, Gardenias can be temperamental when it comes to blooming and even thriving. They can certainly give gardeners a run for their money if growing and care conditions are anything less than just so.
One way to keep plants happy, healthy, and looking their most resplendent is to use a good quality fertilizer. It’s an undertaking that I have given much consideration to of late for these acid-loving shrubs. Here’s my pick of the five best fertilizers for Gardenias that are currently available on the market.
Best Fertilizers for Gardenias
Best Fertilizer Spike For Gardenias
Jobe’s Azalea & Camellia Fertilizer Spikes 9-8-7
A perfect balance of macronutrients for Gardenias and ideal for small, potted varieties or young plants to support strong and vigorous root growth and protect against disease.
Best Slow-Release Granular Fertilizer For Gardenias
Schultz Slow-Release Granules 14-7-7
Perfect choice for season-long Gardenia fertilizing that can also be used as an all-purpose feed for many other acid-loving plants and shrubs.
Best Water-Soluble Fertilizer For Gardenias
Miracle-Gro Water Soluble Miracid 30-10-10
A fast-acting, water-soluble formula with a high nitrogen ratio, intended for ailing plants and to support an increased size and yield of blooms.
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Choosing the Best Fertilizer for Gardenias
Just like Azaleas, Camellias, and Rhododendrons, Gardenias are acid-loving plants, and their soil and fertilizer requirements need to align with these preferences.
Plants require a range of nutrients including macronutrients Nitrogen, Potassium, Phosphorus, and micronutrients including Magnesium, Iron, and Copper.
Anything less than nutrient-rich soil in a soil pH range outside of 5 to 6 means that your Gardenias won’t remain healthy. They will begin to show signs of stress, including stunted growth, bud drop and poor flower production, discolored leaves, and pest and disease infestations.
If you are unsure what the pH levels are in your soil, I recommend using a soil pH test before you plant Gardenias to ensure nutrients are correctly balanced. Correcting levels of acidity take time and are more difficult to achieve once planting has taken place.
Gardenia N-P-K Ratio
The three most vital macronutrients to plants can be found in all fertilizers. Here’s a look at what each of them does:
- Nitrogen (N) – encourages plant growth and leaf development
- Phosphorus (P) – is required for strong roots, fruits, flowers and seeds
- Potassium (K) – promotes growth production and resistance to disease
Plants need each of these macronutrients, but the quantities required will vary from one plant variety to another.
Fertilizer labeling and manufacturer’s websites will provide details of the percentage of each of these macronutrients that are contained per net weight of the product.
These percentages are denoted on the packaging in numbers. For example, a fertilizer with the N-P-K ratio of 9-8-7 would contain 9% nitrogen, 8% phosphorous, and 7% potassium.
Because Gardenias are evergreen, they require a fertilizer with a higher ratio of nitrogen to promote robust foliage growth as a constant.
Ideal Soil pH for Gardenias
The ideal soil pH for Gardenias is acidic at 5.5, but they tolerate a range of between 5.0 to 6.0. Anything higher than 6 means the soil will be too alkaline and unsuitable for planting or growing. As a result, Gardenias may suffer stunted growth, lack of blooms, and yellowing of leaves.
There are several things that can be done to increase soil acidity. For example, you could add well-matured compost or manure before planting. Adding a layer of mulch over winter can also help.
Granules Vs. Liquid Fertilizer
There is a range of different fertilizer types available, including liquids, granules, and spikes.
Plants can’t tell how their nutrients are supplied, and each style of fertilizer has advantages and disadvantages. I recommend choosing a fertilizer that contains the correct balance of N-P-K but also considers your preferred method of application based on how your garden and what other plants you grow.
Liquid Fertilizer
Liquid concentrate formulas need to be diluted with water and provided they are mixed thoroughly, will provide a nutrient content that is identical in every drop.
They need to be watered into the soil around the plant or applied directly to leaves as a foliar spray. Once absorbed, they provide an instant boost of nutrients directly to roots, leaves, or stems.
Run-off is likely to occur with this method of fertilizing so the application must be more frequent. Also, care should be taken to avoid run-off contamination with water sources.
Granular Fertilizer
Granules and powders offer a slow-release fertilizer option. Formulas need to be sprinkled into planting holes, or around the plant itself, or used as a top or side dressing and mixed into the soil well. Water then needs to be applied for activation to commence.
The great advantage of using slow-release formulas is how often you need to apply them. Depending on the brand, formulas can continue to release nutrients from between 4 weeks to 3 months.
Root burn or leaf scorching can occur in some species of the plant if powders or granules get into contact with stems or leaves, or if over-fertilizing – by using too much product – occurs.
Fertilizer Spikes
Spikes are a convenience-led slow-release option. They offer a mess-free and pre-measured approach to feeding plants, trees, and shrubs.
They are simply removed from packaging and pushed or hammered into the soil around the base of the plant. Just like granules and powders, they continue to release nutrients into the soil over a sustained period.
They are often odor-free and easy to store however, they can work out to be the most expensive method of fertilizing especially if you have matured or multiple species to feed.
There is also a risk that roots can get damaged when inserting them into the ground.
Organic Fertilizer
Organic fertilizers are produced using naturally occurring, nutrient-rich ingredients sourced from plant and animal matter.
These all-natural types of feed are sometimes said to be less potent than their chemical-based counterparts and may also exhibit a rather ‘organic’ smelling odor which can be attractive to pets and wildlife.
Unlike synthetic fertilizers, they are less likely to damage plant cell structures that can lead to root burn, and they do not pose a risk to the environment when used correctly.
They are the preferred method of fertilizing for many, especially in edible gardening.
Best Fertilizers for Gardenias
Two key characteristics of a healthy-looking Gardenia are year-round lush glossy foliage and beautiful blooms.
To achieve this, you are going to need a fertilizer that provides the right balance of nutrients to enable robust growth, healthy roots, and an abundance of flowers. You’ll also need a hefty dose of nitrogen to assist with acid levels in soil and maintain leaf production throughout the year.
Pros
- Slow-release of nutrients into soil for up to 3 months
- Non-toxic
- No mess or odor
Cons
- Can crumble when planting in hard ground
These convenient fertilizer spikes make feeding your Gardenias a breeze. They release a gradual dose of feed directly into the soil making it easy for roots to absorb for up to 3 months with no mess or fuss.
The N-P-K ratio of 9-8-7 ensures that both plant and soil get nutrients in the ideal quantities for Gardenias. This helps to maximize glossy foliage, flower production, and overall plant health.
How to Use: Use one spike per foot diameter of the plant. Simply push spikes into the ground around the plant’s base. I recommend watering the soil around your Gardenias before inserting these spikes to avoid breakage.
Pros
- Slow-release of nutrients for up to 3 months
- Value for money compared to other more expensive fertilizing options
Cons
- Can cause scorching if not used correctly
Schultz is a trusted brand that comes with a seal of approval in many gardening circles. This slow-release fertilizer can be used throughout the growing season and it’s good value for money too since it only needs applying once every 3 months.
The high percentage of nitrogen will help to maintain soil health and avoid nitrogen nutrient deficiency in your Gardenias, which is exactly what these plants need.
I used this fertilizer when I noticed yellow leaves which is often a sign of low nitrogen levels. The results were an increase in new shoots and improved overall health of foliage.
How to use: For established plants, apply from early spring onwards. Scatter 4 cups per 100 sq. foot of soil over the surface of the soil and work it in gently.
Avoid product touching the plant itself and causing damage to roots whilst digging in.
Pros
- Fast-acting
- Available in a range of quantities
- Easily absorbed by roots
Cons
- Requires mixing
Miracle-Grow has long been a trusted household name, and this product doesn’t disappoint. When applied according to the manufacturer’s instructions, it won’t burn roots and helps produce abundant growth and large, plentiful blooms.
It works immediately, giving fast results for many acid-loving plants. It is known for its impressive results with ailing Gardenias and can bring about larger and more plentiful blooms.
How to Use: Mix with water at a rate of one pound for every 400 square feet. Feed to exterior plants every 7-14 days.
Pros
- 100% organic containing all natural ingredients
- Helps support healthy growth even in periods of drought
Cons
- Strong ‘organic’ odor
This natural formula from Dr. Earth is an ideal fertilizer for when you know that soil conditions are just right and you want to encourage flower production for your Gardenias.
100% organic, this slow-release formula contains beneficial soil microbes to help roots absorb nutrients quicker. In addition, this feed will increase drought tolerance and improve the overall health of acid-loving plants.
The odor of this fertilizer may not be to the liking of everyone. Expect a strong ‘organic’ smell that is highly attractive to wildlife and pets.
How to Use: Sprinkle the correct amount around the base of the plant, not too close to the stem, and water in.
Pros
- Contains Espoma’s trademark ‘Bio-Tone’ to improve soil
- Only 2 application per year required
Cons
- Strong smell
My next choice is Espoma Organic Holly-Tone Plant Food. This contains 100% natural ingredients and while it may not have the higher dosage of nitrogen it is intended for many varieties of acid-loving plants. Just ensure your soil conditions are nitrogen-rich.
Espoma products are unlike any other fertilizers because they contain a patented ‘Bio-tone microbes’ formula. These microbes help to improve the condition of the soil and once absorbed by roots lead to healthier plant growth. How to use: Use one cup of fertilizer for every 1ft of branch spread. If your blueberry shrub is three feet or larger, double the quantity. Sprinkle the required amount around the dripline and water thoroughly. Apply the first application in early spring and another in fall.
How to Fertilize Gardenias
Gardenias do not require excessive amounts of fertilizer in the same way that some other flowering shrubs do.
Whether you are growing them in pots or in the ground, here below are all the dos and don’ts you need to consider so you can provide the correct amount of nutrients and avoid over-fertilizing.
Over Fertilizing Gardenias
Less is more when it comes to fertilizing Gardenia plants, especially if you are already providing them with the nutrient-rich acidic soil that they need to thrive.
Using a fertilizer with a low ratio of N-P-K such as 9-8-7 will help to avoid leaf or root burn. If you are concerned about the potential for scorching, you could use half quantities of feed.
Using slow-release granules means you can reduce the number of times you need to apply fertilizer and this will help to reduce any build-up of fertilizer in the soil that may otherwise build up and cause stress to your plants.
Watering between feeds will also help to flush out excesses of fertilizer that remain in the soil.
Over-fertilizing Gardenias can affect leaves, flowers as well as the overall health of your plants. Symptoms include yellowing and wilted leaves (especially in the lower region of the plant), leaves with brown tips, and very slow or no growth at all.
Any one of these symptoms can result in bud drop and a lack of flowers and will diminish your plants’ ability to thrive.
Fertilizing Gardenias in Pots or Containers
Gardenias grown in pots or containers will need fertilizing and watering more often than those planted in the ground due to the run-off that occurs through drainage holes.
The soil in pots and containers also tends to become depleted of nutrients more quickly.
Water-soluble fertilizers offer a solution that allows for more frequent fertilizing without the risk of over-fertilizing. It also provides the chance to water your Gardenia more frequently than you might need to compare with ground-planted varieties.
When to Fertilize Gardenias
Begin fertilizing Gardenias in early spring once the threat of frost has passed. Follow the recommendations provided by the fertilizer manufacturer on when to fertilize thereafter during the summer months.
Make sure you apply fertilizer in the fall before temperatures drop too dramatically. This will help to improve nutrient depletion in soil that may have taken place during the summer months.
There is no need to apply fertilizer during the winter months, however, applying a layer of mulch to cover the soil around your Gardenias will help to maintain acidity in the soil.
How Often to Feed Gardenias
Gardenias are not heavy feeders and therefore frequent feeding is not necessary.
How often you do fertilize will depend on your chosen application method. Water-soluble options will need to be applied more due to run-off. Slow-release spikes and granules need applying less frequently. Often once every 3 months.
Either way, Follow the instructions provided by the manufacturer of your fertilizer product to help maintain the healthy growth of these beautiful evergreens.
Verdict: Best Fertilizer for Gardenias
Choosing the best fertilizer for your Gardenias can seem like an overwhelming process but it’s easy when you know what you’re looking for.
If you have a small number of Gardenia plants that are generally in good health and planted in nutrient-rich soil, then I recommend you choose Jobe’s Azalea & Camellia Fertilizer Spikes 9-8-7. These offer the exact N-P-K ratio that these plants need.
For a more cost-effective equivalent, especially if you have a selection of Gardenias or more mature plants, I suggest you buy Schultz Slow-Release Granules 14-7-7. These have a larger ratio of nitrogen which will promote soil health and encourage that all-important lush, glossy foliage.
If it’s ailing Gardenias that need a boost, I highly recommend Miracle-Gro Water Soluble Plant Food. The 30% nitrogen ratio and fast-acting formula will quickly help to bring vibrancy and health back to Gardenias and other acid-loving plants. As well as help to improve nutrient-deficient soil.
Best Fertilizer Spike For Gardenias
Jobe’s Azalea & Camellia Fertilizer Spikes 9-8-7
The perfect balance of macronutrients for Gardenias and ideal for small, potted varieties or young plants to support strong and vigorous root growth and protect against disease.
Best Slow-Release Granular Fertilizer For Gardenias
Schultz Slow-Release Granules 14-7-7
Perfect choice for season-long Gardenia fertilizing that can also be used as an all-purpose feed for many other acid-loving plants and shrubs.
Best Water-Soluble Fertilizer For Gardenias
Miracle-Gro Water Soluble Miracid 30-10-10
A fast-acting, water-soluble formula with a high nitrogen ratio, intended for ailing plants and to support an increased size and yield of blooms.
