6 Best Fertilizer For Petunias And Geraniums | How And When To Use

Gardeners, worldwide, are well-versed with the profusion of color that petunias and geraniums provide during seasons of warmth and light. Petunias, in every size and color, have been adorning patio pots and hanging baskets since the mid-1800s. 

With over 400 different varieties, the humble geranium conjures up images of vibrant waterfalls cascading over wrought-iron railings and stone steps. How do we keep our plants happy, healthy, and providing that dreamy profusion of color? By finding the best fertilizer for petunias and geraniums on the market. 

Best Fertilizer For Petunias And Geraniums 

Aside from their beauty, these fervent bloomers are known for their ease of care. Lots of sunshine, nutrient-rich soil, and a steady stream of feed that meets their N-P-K needs. 

While both are heavy feeders, their nourishment requirements are simple. A 5-10-5 for geraniums and a 5-10-10 for petunias is a good rule of thumb. 

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Granular Vs Liquid Fertilizer 

Which to choose mostly depends on your preference and end-result expectations. 

  • Liquids can save time as nutrients are quickly carried to the roots, allowing for immediate uptake. Liquids  can also balance pH levels.
  • Heavily concentrated, slow-release granules provide consistent nourishment for several months at a time.

Liquid Concentrate Or Spray 

Water-diluted concentrates work through either root absorption or as a foliar spray. This can be long-lasting and cost-effective with a little bit going a long way. And concentrated cakes can sit on your potting shelf, with no mess, until you’re ready to use them.  

Fertilizer Granules Or Powder 

Granules are slow-releasing, providing consistent nourishment for up to nine months. Delivering nutrients with every watering.

Powders can be sprinkled around as a slow-release or diluted in water for faster absorption. While powders are cheaper, they carry a risk of root burn if not applied properly.

Fertilizer Spikes 

Spikes are one of the easiest to use. Pre-measured and slow-releasing (with little risk of root burn), nutrients are released by micro-organisms that live in the soil. This particular method of application also carries the added benefit of stimulating an increased resistance to tree disease and pests. 

Fertilizer N-P-K 

Petunias and geraniums are happiest when they’re given the right combination of macro-nutrients such as nitrogen (N) – for healthy foliage, phosphorus (P) – for strong roots, and an abundance of blooms and potassium (K) – for durable resistance to disease. Producing all those flowers does take a lot of energy making them heavy feeders, so a 5-10-5  or 5-10-10 NPK is recommended.

PRO TIP – What Exactly Is an NPK?

Every fertilizer label displays a three numbered ratio, known as an N-P-K. Indicating its proportions of nitrogen, phosphorus, and potassium. Example: 5-10-5 means 5% nitrogen, 10% phosphorus and 5% potassium. 

Fertilizing In Pots Or Hanging Baskets 

In baskets or pots, the best fertilizer will provide your flowering annuals with the most beneficial NPK combination. Potted plants naturally absorb nutrients a lot faster, so more frequent applications may be needed. There’s an important balance, though. They can just as easily become over-fertilized and suffer. 

Fertilizing Petunias In Hanging Baskets 

Keep in mind that while a good fertilizer encourages vigorous growth, too much has the same effect on roots. Out-of-control roots, limited by their container, can lead to your plants becoming root-bound. The trick is to apply lower doses of feed at a higher frequency. 

Fertilizing Geraniums In Pots 

The same idea applies to potted geraniums. As heavy feeders, their roots too will still be limited by pot size. You can use a slow-release fertilizer to release just the right amount with every watering. Without risking root burn or rapid overgrowth of roots or foliage. 

Best Fertilizer For Geraniums And Petunias 

Product testing and review research takes time, effort, and money. For your convenience, I’ve done some extensive testing of my own. Including consumer experiences from all across the gardening spectrum. Below are my picks for the top 6 best fertilizers for these prolific bloomers.

1. Dr. Earth Organic Bud & Bloom Fertilizer 3-9-4

Dr. Earth Organic Bud & Bloom Fertilizer 3-9-4

Dr. Earth’s bloom booster is an organic formula that offers bigger buds and more of them so your petunias and geraniums will keep coming and provide vibrantly colored blooms all through the growing season. Which is just what you want for hanging baskets and pot or container arrangements in your outdoor space.

This fertilizer is enhanced with no less than seven strains of soil microbes all of which contribute towards maintaining soil fertility. I was delighted to find that my petunias produced more buds and healthy foliage than I would otherwise have expected.

Check the prices of Dr. Earth Bloom Booster here

How To Use: Apply the recommended amount every other month, as either a water-soluble tea or a dry soil additive.

Customer Reviews: Natural gardeners who incorporate flowers into recipes were so pleased to see the results they saw from this organic product. Knowing the blooms were safe to eat. Awarding this 4.7 out of 5 stars and my pick for BEST BUY.


  • Organically provides an abundance of blooms
  • Versatile for use as a quick or slow-release


  • Overuse may raise pH levels in soil

2. Jack’s Classic Blossom Booster Fertilizer 10-30-20 

Jack’s Classic Blossom Booster Fertilizer

Jack’s Classic is a formula rich in phosphorus and potassium and that always equals abundant blooms and foliage when it comes to flowering annuals.

I was comfortable testing this on my hanging baskets because the slightly lower nitrogen content means roots tend to grow at a slower rate than foliage and buds which is perfect for container plants that are intended to last just for the summer season.

Season-long, Jack’s did not disappoint. Even after the first dose, I saw double the number of buds and great color when they opened. Click for Jack’s Classic Bloom Booster here at Amazon.com

How To Use:  Mix 1 teaspoon per gallon of water. And apply to potted plants and hanging baskets once per week. 

Customer Reviews: Using this product, gardeners were amazed at how long their plants continued to bloom. Extending their growing season far beyond expectation, complete with color and fragrance. 4.8 out of 5 stars.


  • Quick dilution for use with watering cans or hose attachments
  • Extends bloom time beyond expectation


  • Not recommended for plants growing in compost-enhanced soil

3. Jobe’s Hanging Basket & Potted Plant Fertilizer Spikes 8-9-12

Jobe's Hanging Basket & Potted Plant Fertilizer Spikes

I find that Jobe’s spikes are really convenient when time is limited. They offer a consistent release of nutrients that are released directly to the roots and can last for up to 8 weeks.

In mid-summer, the intense heat can really start to show in potted plants despite our best efforts to keep on top of a watering regime. I found that the second application of these spikes helped to increase the resistance to environmental stresses.

With Jobe’s, my geranium and petunia display continued to bloom in abundance without the dreaded onset of early yellowing of leaves

How To Use: Insert the recommended number of spikes (per size of the pot) around your plants every 8 weeks, throughout the growing season.

Customer Reviews:  Customers who typically buy new plants toward the end of the season, to maintain the look of their gardens, no longer need to with Jobe’s spikes. Saving them time and money while enjoying bountiful, season-long color. 4.6 out of 5 stars.

Click here for Jobe’s Hanging Basket & Potted Plant Fertilizer Spikes.


  • Increases resistance to environmental stresses
  • Easy to use and easy to store


  • Maybe at a slighter higher price point

4. Miracle-Gro Bloom Booster Flower Food 10-52-10 

Miracle-Gro Bloom Booster Flower Food

No complete comparison is without Miracle-Gro. The phosphorus-heavy NPK guaranteed a profusion of blooms by stimulating enzymes that triggered bountiful bud and seed production in my petunias and geraniums.

A tip, though. Pinching off all the spent flowers stimulates the production of more. If you leave them on, all the plant’s energy will start to focus on seed production. Check out Miracle-Gro Bloom Booster Flower Food here.

How To Use: In a watering can mix 1 tablespoon of Miracle-Gro per one gallon of water.

Then, soak the base of your plants every 7-14 days.

Customer Reviews: Even gardeners with slow-to-bud, partial-shade bloomers responded far better than expected with Miracle-Gro. Giving their flowering plants the extra motivation they needed to produce an abundance of blooms. Highly recommended at 4.8 out of 5.


  • Plentiful flowers in just a few days
  • Easy to use and store


  • Multiple boxes may be needed for larger gardens

5. Ferti-lome Blooming & Rooting Plant Food 9-58-8 

Ferti-lome Blooming & Rooting Plant Food 9-58-8

This water-soluble option from Ferti-Lome focuses on overall plant health. From promoting robust root development right through to encouraging an abundance of blooms as well as foliage.

This was the first year I noticed just how large geranium leaves could grow and the contrasting vein color was just stunning against the vibrant color of the blooms. It’s quite normal to see some yellowing of leaves by mid-august but this didn’t happen on any of the flowering plants I tested whilst using this.   

Check prices for Ferti-Lome Blooming & Rooting Soluble Plant Food here.

How To Use: Mix 2 tablespoons into 1 gallon of water in a watering can. Repeat every 1-2 weeks during the growing season.

Customer Reviews: First-time buyers are sharing they’ll now be repeat customers after trying this product. Seeing fantastic results in everything from hanging baskets and vegetables to small border plants and large shrubs. 4.8 out of 5 stars


  • Targets overall plant health from robust root support through to encouraging large, vibrant foliage and flowers
  • Versatile enough for ornamentals and can also be used as a vegetable fertilizer


  • Not recommended for use on phosphorus-sensitive plants

6. Scotts Super Bloom Plant Food 12-55-6 

Scotts Super Bloom Plant Food

Scotts water-soluble, phosphorus-rich formula promises instant feeding while protecting against root burn when used as directed.

I live in a short growing season area so I have to start plants indoors. This proved highly effective on new seedlings in early spring. Click here for Scotts Super Bloom Plant Food.

How To Use: Pre-moisten soil prior to application. Then mix two teaspoons into each gallon of water used and water normally. Repeat every 7-14 days. 

Customer Reviews: Gardeners have tried this with a watering can, hose attachment, and backpack sprayer. All with surprising results. Even plants that were thought to bloom only once, continue to do so all season with consistent feeding. 4.6 out of 5 stars


  • Effective in both harsh and temperate climates
  • Extended bloom times on single season bloomers


  • Frequent waterings may be necessary to avoid root burn

How To Fertilize Geraniums And Petunias 

Waiting to fertilize until transplants are well-established is key. But once they are, they will emphatically respond to a steady stream of nutrients. Every 1-2 weeks is a good rule-of-thumb to follow, for liquid feeds, and every 6-8 weeks for slow-release applications.

Feeds with a balanced NPK will promote the overall health and productivity of your plants without overwhelming the soil. Allowing the possible re-use of it next season. 

Fertilizing For Better Flower Bloom 

If you’re looking for a big show, fertilizers rich in phosphorus will provide just that. However, those plants may have to be watered more frequently to avoid root burn. High doses of phosphorus push bud production into high gear while moving it toward maturity faster.  

Soil PH For Petunias And Geraniums 

Soil pH levels determine a plant’s ability to absorb nutrients. Too high and nourishment is blocked. Too low and the plant becomes vulnerable to pests and disease. Petunias and geraniums prefer a slightly acidic environment (or a pH) between 6.0 and 7.0. Beware that some fertilizers can alter the balance of soil pH so it’s best to check the levels in your soil using a soil test kit.

Over-Fertilizing Petunias And Geraniums 

Achieving abundant flowering while not endangering our plants is entirely possible providing you follow the manufacturer’s recommendations for correct application rates. Whilst over-fertilizing may well create an initial explosion of color, this is often short-lived and plants will some become more vulnerable to disease and root burn. A healthy balance of nutrients, on the other hand, will provide you with beautiful plants, season after season. 

When To Fertilize Geraniums And Petunias 

Fertilizing can start anywhere from early March to May and continue throughout the growing season until mid-autumn. Early morning or late afternoon is the best time to apply liquid feeds as this avoids foliage burn that can be caused by the intense heat of the sun.

How often you fertilize will all depend on the product you buy and the specified application method.

How Often To Fertilize Geraniums 

Geraniums require water-soluble applications generally every 2-3 weeks. Slow-release options, roughly every 6-8 weeks. Soil mixed with sand, pumice, or coco coir has a higher drainage value causing nutrients to leach out faster.  So, more frequent feedings may be needed here as opposed to denser soil that tend to hold nutrients for longer. 

How Often To Fertilize Petunias 

Petunias, like geraniums, are heavy feeders, so you’ll need to consistently fertilize these, as well. For potted petunia varieties, every two weeks will be effective. For carpet or spreader petunias that are grown in the ground, a weekly feeding is recommended. 

Verdict: Best Fertilizer for Petunias And Geraniums 

The verdict is in! The best fertilizer for petunias and geraniums is going to be the one that guarantees a profusion of color in your planters and hanging baskets throughout the summer. It is also going to be the one that fits your needs and meets your end-result expectations.

For organically grown plants that produce healthy foliage and vibrant color, Dr. Earth’s Bud & Bloom Booster is the one for you. For a fast abundance of blooms that you need to arrive in a hurry, perhaps for a special occasion, Jack’s Classic Blossom Booster or Jobe’s Hanging Basket & Potted Plant Fertilizer spikes will get you there. Jack’s is a water-soluble fast-acting formula, while Jobe’s provides convenience, less mess, and a slow-release solution.

Fertilizing Petunias And Geraniums FAQ’s