6 Best Fertilizer for Sunflowers | How and When to Use

If you’re looking to add a little “happiness” to your garden, then you’ve come to the right place. Sunflowers have been grown for centuries to attract beneficial soil microbes, which improve soil fertility.

These cheerful bloomers also bring essential pollinators to your garden. Which can increase crop yield and quality.

Sunflowers aren’t fussy about their growing conditions. But, in poor soil, the right fertilizer for sunflowers can make all the difference, in terms of size, color vibrancy, and seed production. All these characteristics bring joy to our garden spaces.

The Best Sunflower Fertilizers 

For effective tips on increasing sunflower color and size, be sure to read all the way to the bottom. But if you’re in a hurry and just need my top recommendations, take a look at these two products below, all of which have consistently produced fantastic results for me.

Down to Earth Organic Bone Meal Fertilizer 3-15-0 

Best Organic Fertilizer

1. Down to Earth Organic Bone Meal 3-15-0 

Rich in naturally occurring phosphorus derived from Bonemeal to optimize root and flower development. Effective for up to four months.

Jack's Classic Blossom Booster Fertilizer 10-30-20 

Best Water-Soluble Fertilizer

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

Fast-acting water-soluble formula to enhance poor soil conditions, and increase yield and blooming time.

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Choosing A Fertilizer for Sunflowers 

Sunflowers are very heavy feeders, and to maximize their flowering potential, they require a high level of phosphorus to assist with strong root development and to draw all available nutrients from the soil.

Agricultural growers typically use an NPK ratio of 20-30-20kg of fertilizer per hectare. This means 20% Nitrogen, 30% phosphorus, and 20% potassium, (NPK 20-30-20) as well as trace minerals such as calcium, sulfur, boron, and magnesium.

Realistically, fertilizing your backyard in the same way as an agricultural farmer is not always possible, or necessary. So keeping it simple yet still effective, any NPK ratio with high phosphorus is perfect. Use an organic bone meal fertilizer 3-15-0 which is high in phosphorus, or a bloom booster fertilizer 10-30-20, developed specifically with flowering plants in mind.

So the focus is on strong root development to support flowering, hence the high phosphorus. The other nutrients are generally available and abundant in your garden soil. Think about it, your garden soil is nowhere near as depleted of nutrients as agricultural land, which is why farmers’ fields need heavy fertilization every year.

Understanding N-P-K Ratio 

Choosing an appropriate NPK combination is an important part of nourishing your plants. But try not to get too hung up on it, as different soils and even different methods of irrigation affect how NPK ratios work in practice. Just in case you are not clear on what an NPK ratio is, let’s cover that topic in a little bit more detail.

What is an NPK ratio, exactly? Fertilizer labels show a three-numbered formula, indicating its proportions of nitrogen, phosphorus, and potassium. For example, a 10-18-9 NPK has 10% nitrogen, 18% phosphorus, and 9% potassium. Each of the three macronutrients plays a slightly different role in plant growth. Nitrogen support vegetative growth, phosphorus produces healthy roots, and potassium (potash) creates large flowers or fruits. However, there is a significant crossover between these three nutrients where they are co-dependent on each other and trace elements.

Sunflower Soil pH and Nutrient Uptake 

Sunflowers, like all other plants, thrive in a specific soil pH range. If the soil is outside of this pH range, meaning it is too acidic or too alkaline, then the sunflower will not be able to process the available nutrients and therefore struggle to grow.

Sunflowers require a soil pH of 6.0 to 6.8. So make sure you test your soil before applying any type of fertilizer, otherwise, you may be wasting your time and money. You can amend soil pH with the application of sulfur or lime, both will be available from any good gardening center.

Granular or Liquid Fertilizer 

You can choose either a liquid feed that is typically diluted with water and used during watering or a granule fertilizer that is most often sprinkled onto the soil surface.

Liquids quickly carry nutrients to the roots, allowing for immediate uptake. They can keep pH levels balanced, too. But caution is recommended, as over-use could lead to root burn.

Granules offer a slow-release effect often called controlled release, which provides nutrients over a period of several months, saving time and effort.

Fertilizer Granules 

Granules are slow-releasing and provide nourishment for much longer. This means less work and more garden enjoyment for you. These are also far less likely to cause root burn.

Nutrients are released by warming temperatures. Then consumed and converted into an easily absorbed form by soil microbes. 

Fertilizer Spikes 

There are many interesting options on the market and a relatively new product is the fertilizer spike. These are pre-measured sticks available in various sizes, that you push into the soil where they release nutrients in a controlled release way, similar to granules. 

I would recommend this type of product if you are growing just a few specimen sunflowers, where just a few spikes can be used over the season. Personally, I like to stay with the more conventional top dressing for sunflowers, as it’s more cost-effective and you can broadcast across the whole root system.

Organic or Synthetic

Choosing between an organic or synthetic fertilizer for sunflowers is a simple matter of gardening style and end-result expectations. 

Organics contain nutrient levels similar to what plants receive in the wild. They can nourish your plants for longer while improving soil fertility.

Inorganics are mass-produced using minerals and synthetic chemicals. These can produce bigger plants with larger blooms but can also potentially contaminate nearby water sources and your soil. 

Best Sunflower Fertilizer Reviews 

Product testing and consumer review research take time and effort. For your convenience, I’ve done some extensive testing on several different sunflower varieties in my own garden. Based on performance and ease of use. Below are my picks for the top 7 best fertilizers to improve the blooming of healthy sunflower plants. 


  • There are very few products as good as bone meal when it comes to flowering plants and Down To Earth product an exceptionally high-quality product
  • Includes all of the vital micronutrients for strong flower production


  • May exhibit a mild organic earthy odor 

These slow-releasing bone meal granules last for up to four months. It’s one of those products that makes me feel good using in my garden. Like all products from Down To Earth, it’s organic and packed with fantastic ingredients, making it my pick for the best organic fertilizer.

A bonemeal with a 15% ratio of phosphorus means that, when used right from the planting stage, sunflower roots are given the best possible start in getting quickly established. With regular application throughout the growth cycle, my sunflowers grew tall and put out an impressive number of flower heads. Despite regular use, I found no detrimental effects from burn, or chlorosis.

Following on from this trial, I will continue to use this fertilizer more often, as it gave me the option of using it on transplants and feeding moderately right through each growth stage. I think this continual use paid dividends when compared to applying one or two applications of stronger synthetic fertilizers.

How To Use: New transplants – mix in 1-2 tbsp per hole, then water well. For established plants – side dress with 2-4 oz per month during the growing season.


  • Quick dilution for use with watering cans or hose attachments
  • Also good for extending the bloom time of hydrangeas, azaleas, and roses amongst a long list of popular show-stopping flowers


  • Not recommended for plants growing in heavily composted soil 

If you’re looking to grow large, heavy feeders in poor soil, there are a few better options than the nutrient-rich formula from Jack’s. Despite the high NPK ratio I opted to use it at 70% of the manufacturer’s instructions, so effectively I applied it as 7-21-14. I felt this would be a better ratio for a liquid product that was being watered in.

It was easy to dissolve and produced impressive results when applied every four weeks. The downside for me was my hesitation to use it on the plants until they were around 12 inches high, maybe I lost a little bit of the plant’s potential. The formula just felt too strong to use too early on, but that was just me.

As the plants matured not only did I see healthy-looking vegetative growth and strong stems, The plants produced a ridiculous number of flower heads. Jack’s was by far the most effective product for increasing flower yield.

How To Use: Mix 1 teaspoon per gallon of water. Then, apply to ground-planted sunflowers once per week. Potted plants will need further dilution, based on plant and pot size. 


  • Increased color vibrancy in just a few days
  • Easy to use and store


  • Multiple boxes may be needed for sunflower groves

No review comparison for flowering plants is complete without Miracle-Gro Bloom Booster. The phosphorus-heavy NPK guarantees healthy nitrogen absorption in lacking soil and increases the process of effective photosynthesis by producing vibrant green foliage and bright, sunny flowers.  

As you would expect from the market-leading brand the results were as impressive as Jacks, in terms of flower yield. However…the Miracle-gro Bloom Booster is much more expensive pro-rata than Jacks, so this plays a part in why I have it lagging behind.

If a soil test has revealed a lack of phosphorus in your soil or if your flowering plants don’t seem to be responding to other fertilizers, this may be an effective choice for you.

How To Use: Mix 1 tablespoon of Miracle-Gro per one gallon of water. Then, soak the base of your plants. Repeat every 7-14 days. 


  • Another great bone meal product, ideal for supporting strong flower growth
  • This product also helps to loosen heavy, clay soil, supporting deeper root growth


  • Can attract wildlife such as rodents or deer due to its natural odor

This bone meal from Espoma comes in granular form and has over time gained a well-deserved reputation. The beauty of bone meal is its versatility across a whole range of flowering plants and root vegetables. So if you’re like me and you grow your sunflowers in your vegetable garden this will be a great option to broadcast across the whole plot by hand and let the rain do the work of watering it in for you.

It does have a fairly strong smell to it so you may choose a different product if you have problems with pests or deer.

How To Use: Apply 1 or 2 pounds depending upon the size of your ground surface area. Apply 2 oz or one heaping tablespoon, per potted plant and work into the soil. 


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


  • Regular watering may be necessary to avoid root burn on young plants 

Scotts water-soluble, phosphorus-rich formula offers the benefits of delivering a very direct feed in liquid form to be soaked up and use to good effect in producing strong growth. The ratio of phosphorus is very high in this super bloom product, so it is best used during the middle period of the vegetative growth stage as a booster. Avoid using this on young tender plants.

I live in a short growing season area, so I have to start sunflower seeds indoors. This proved highly effective after planting out seedlings, in early spring letting them grow on, then giving them a boost as they begin to show signs of flower development.

How To Use: Wet soil prior to applying the fertilizer. Mix two teaspoons into each gallon of water used and water normally. Repeat every 7-14 days. 


  • Easy to use and available at just about any gardening store
  • Includes essential secondary micronutrients such as calcium and magnesium


  • Not recommended for fully fertile soil 

If you are happy using a synthetic product, there are not many options on the market that produce the kind of results Miracle-Gro does. I guess that’s why it’s the number-one bestseller.

When using this Shake and Feed product, the bloom color is vibrant, I used it on a potted sunflower, and it performed very well when compared to a plant fed with home-produced potting compost.

This product is formulated to be attractive to hungry soil microbes, which then convert nutrients into a readily available form. 

How To Use: Apply dry and evenly to the soil, approximately 1 tbsp per sq ft for a consistent feeding that lasts for three months.

You will also enjoy reading What To Grow With Sunflowers | Companion Plants

How to Fertilize Sunflowers 

Sunflowers are heavy feeders and deplete soil faster than most other flowering plants. But, if you regularly add compost and other organic materials, soil depletion will be a rare event, and your sunflowers will reach great heights. Giving you the happy effect you’re after. 

If you’re not able to do so, no worries. Feeding your flowers an NPK ratio that provides what your soil is lacking will mean success! 

Avoiding Sunflower Fertilizer Burn 

Fertilizer burn usually occurs when the gardener is overly keen on the application of synthetic products. It’s normal to think that the more feed you apply the better the plant will grow. In my experience, it never pays to overfeed any plant, and in fact, I would recommend feeding at a rate of 50-75% of the stated manufacturer guidelines.

The application of excess potassium and phosphorus will introduce salts into the soil that can quickly absorb all available moisture, leading to the plant suffering from dehydration.

When to Fertilize Sunflowers 

When you fertilize your sunflowers depends on the fertilizer formula and method of application you choose. 

Granules and spikes can be applied to annuals or perennials during spring. For annuals apply very low doses after transplanting, or when seedlings show the 2nd set of leaves. Dig the fertilizer into the soil and do not place it in piles around the base of the plant, otherwise, it may cause fertilizer burn.

Liquid fertilizer, being stronger, should only be used when nutritional demands require it and only when sunflower plants have somewhat matured. 

How Often to Fertilize Sunflowers 

The frequency of sunflower fertilization may also be dictated by the product formulation. Down to Earth’s bone meal needs applications every 4 weeks. Versus Espoma’s formula, which I only recommend using twice per season. 

Granules, like Scotts Super Bloom and Miracle-Gro’s dry shake n’ feed, should be applied every two weeks to three months, respectively. 

Verdict: Best Fertilizers for Sunflowers 

So, the verdict is in. If you have super-fertile soil, you might not really need to supplement any nutrients, at all. But remember, sunflowers are heavy feeders, and even fertile soil sometimes finds itself in need of a quick boost. In this case, you should go for Down to Earth Organic Bone Meal.

Down to Earth Organic Bone Meal Fertilizer 3-15-0 

Best Organic Fertilizer

1. Down to Earth Organic Bone Meal 3-15-0 

Rich in naturally occurring phosphorus derived from Bonemeal to optimize root and flower development. Effective for up to four months.

For sunflowers growing in poor soil, a quick boost from Jack’s Classic high-ratio formula will get your soil and plants on the road to growing success. As will Miracle-Gro’s bloom-boosting NPK.

Jack's Classic Blossom Booster Fertilizer 10-30-20 

Best Water-Soluble Fertilizer

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

Fast-acting water-soluble formula to enhance poor soil conditions, and increase yield and blooming time.

Remember, for optimal sunflower growth, including strong roots, robust stalks, healthy foliage, and vibrant, long-lasting flowers that are plentiful, the most effective fertilizers will primarily depend on soil quality and any nutrient deficiencies therein. 

FAQ’s Fertilizing Sunflowers

Do sunflowers need much fertilizer?

Sunflowers are relatively low-fertilizer plants. Excessive fertilizer can lead to tall, weak stems and fewer flowers.

Do sunflowers like nitrogen fertilizer?

Sunflowers benefit from nitrogen, which promotes healthy leaf and stem growth. However, excessive nitrogen can hinder flower development.

Is Miracle-Gro potting soil good for sunflowers?

Yes, Miracle-Gro potting soil can be suitable for sunflowers, providing they’re grown in containers. However, mixing in garden soil or compost is advisable for better drainage and nutrient balance.

What do you add to sunflower soil?

Adding well-rotted compost or organic matter to sunflower soil can enhance its structure, drainage, and nutrient content. It helps provide a balanced environment for healthy sunflower growth.

Do sunflowers like Epsom salt?

Epsom salts are magnesium sulfate. If your soil pH is too high or too low, the magnesium, sulfur, and oxygen in these salts may be a good option.

It’s often used on flowering crops to help increase the number of buds. In addition to being beneficial for new sunflower seedlings and chlorophyll production in older plants, studies have even found that magnesium sulfate helps increase the absorption of key nutrients.

When applied in the right amount and frequency, leaf chlorosis (yellowing) and stunted plant growth could be a thing of the past.

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