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 the characteristics that bring joy to our garden spaces.

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 simply need fast, reliable advice for the best fertilizer for these sunny bloomers, just skip to my picks for the 6 best fertilizer options available. 

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

Best Organic Fertilizer

Down to Earth Organic Bone Meal Fertilizer 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

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

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

Choosing the Best Fertilizer for Sunflowers 

Sunflowers are heavy feeders. The bigger the variety, the faster they’ll absorb nutrients. Planting them in fertile soil, that’s been amended with well-aged compost and other organic materials, is ideal.

But realistically, that’s not always possible. Luckily, there are some fantastic fertilizer options out there that will provide your plants with exactly what they need. The best NPK ratio, though, depends on your soil condition and the variety you’re growing.

Sunflowers require nitrogen, phosphorus,  and potassium to thrive. But, how much of each do they need? Let’s start with what an NPK ratio is. 

Sunflower Fertilizer N-P-K Ratio 

Choosing the right NPK combination is key to properly nourishing your plants. Throughout my picks list, you’ll see different ratios for different soil conditions. 

What is an NPK ratio, exactly? Every fertilizer label includes 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. Every plant requires these elements for optimal health. Just in different proportions. 

Phosphorus and Calcium 

Nitrogen is the nutrient most used by sunflowers. Yet, phosphorus and calcium make that vital use much more efficient at forming healthy roots, stalks, leaves, and flower heads.

Calcium, alone, increases potassium and phosphorus absorption, which facilitates photosynthesis. Improving overall plant health and leaf and flower size. 

Sunflower Soil pH and Nutrient Uptake 

Sunflowers thrive in a pH range of 6.0 to 6.8. Adding well-aged compost to your soil will achieve this at a healthy pace. Or you can choose a fertilizer that will aid in this effort. 

When the pH is too low, nutrients are absorbed in excess of what your plants need. Too high and the opposite happens. Nutrients are locked in the soil and unavailable to roots. 

Granular Vs Liquid Fertilizer 

The difference between these is simply a matter of what works best for you. Yet, each carries different benefits and levels of risk. 

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.

Concentrated granules are slow-releasing and provide consistent nutrition for several months at a time. Saving you time and effort. 

Liquid Concentrate or Spray 

A water-diluted mixture of concentrated nutrients works through either quick root absorption or as a foliar spray. This can prove a cost-effective choice. A little liquid concentrate goes a long way and can be stored, with no mess, until you’re ready to use them.  

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 

Spikes are highly convenient. Pre-measured in various sizes, they’re easy to push into loamy soil and release nutrients in a manner similar to granules. 

Offering the same long-term benefit, spikes also run little risk of plant burn. As a result, they’re considered more “eco-friendly” options, despite some brands being inorganic. 

Organic vs Synthetic Fertilizers 

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

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. 

Pros

  • A readily available source of organic nutrients
  • Includes vital micronutrients for optimal plant health

Cons

  • May exhibit a mild organic earthy odor 

These slow-releasing bone meal granules last for up to four months. It’s one I really feel good about using around my sunflowers and throughout my garden. Making it my pick for the best organic fertilizer.

The 15% ratio of phosphorus means that, when used right from the planting stage, sunflower roots are given a helping hand in getting quickly established and continued usage throughout the growth cycle will yield an abundance of vibrant blooms.

These granules performed really well in delivering a steady flow of calcium which in turn improved nitrogen absorption and effectiveness. The end result was taller stalks and larger flowers, even on smaller varieties.

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.

Pros

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

Cons

  • Not recommended for plants growing in heavily composted soil 

For growing large, heavy feeders in poor soil, there’s no better option than this nutrient-rich formula from Jack’s and the great news is, you can adjust the amount of fertilizer to water ratio, depending on your requirements.

This water-soluble option gets to work instantly by nourishing large-variety sunflowers that are growing in everything from optimal soil quality to less-than-desirable conditions. 

Not only did I see healthy plants that produced generous-sized sunflowers, but longer-lasting bloom times on other flowering plants, as well.

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. 

Pros

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

Cons

  • 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.  

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. 

Pros

  • All-natural source of organic phosphorus and nitrogen
  • Helps to loosen heavy, clay soil

Cons

  • Not recommended for plants that require higher potassium
  • Can attract wldlife such as rodents or deer

This granular bone meal from Espoma should be a staple in your gardening arsenal. When mixing my soil, in spring, I’ll add a dose of this throughout my annual and perennial beds.

The natural phosphorus and nitrogen this provides can’t be beaten for providing flowering plants in less-than-fertile soil with the kind of growing power they need for abundant blooms. Especially if you’re an organic gardener. 

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. 

Pros

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

Cons

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

Scotts water-soluble, phosphorus-rich formula promises instant feeding while protecting against root burn when used as directed. The percentage of nitrogen and potassium is lower, in this NPK, for soil that already contains them. Preventing the overgrowth of foliage with few flowers.

I live in a short growing season area, so I have to start sunflower seeds indoors. This proved highly effective on new seedlings in early spring and then I can continue to use it throughout the growing season. 

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. 

Pros

  • Contains natural ingredients attractive to soil microbes
  • Includes essential, secondary micronutrients

Cons

  • Not recommended for fully fertile soil 

Compared to the liquid, bloom-boosting formula, this granular option worked best in the semi-fertile and sometimes depleted, the soil around my smaller, potted sunflowers.  In fertile soil, I found that higher nitrogen resulted in excess foliage growth. 

When using this Shake and Feed product, the bloom color was more vibrant when compared to a plant that was just fed with home compost. I also no longer saw browning around the edges of leaves.

This is formulated to be attractive to hungry soil microbes who 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.

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 is typically caused by overuse, so it’s important to follow the manufacturer’s instructions. 

Excessive nitrogen can burn roots when applied to the soil and leaves when sprayed. Extra potassium and phosphorus can introduce needless salts that quickly absorb all available moisture, dehydrating your plants. 

When to Fertilize Sunflowers 

When to fertilize your sunflowers will depend on the formula and application method of your chosen fertilizer. 

Granules and spikes should be applied to annual varieties in spring, just after transplanting or when seedlings show the 2nd set of leaves. Perennials will benefit from the same, as new growth emerges.

Liquid options, 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 which case, you should plump for Down to Earth Organic Bone Meal.

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

Best Organic Fertilizer

Down to Earth Organic Bone Meal Fertilizer 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

Jack’s Classic Blossom Booster Fertilizer 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