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9 Best Fertilizers for Watermelons – A Buyers Guide

9 Best Fertilizers for Watermelons – A Buyers Guide

Watermelons or Citrullus Lanatus love the heat and humidity; in fact, they are the symbol of summer. These flowering plants produce big fruits in the summer months. 

Watermelons classify as a fruit and vegetable because they are related to the squash and cucumber family. 

This summer favorite has about 1200 varieties, but all of them need a good fertilizer to produce the best yield. 

Pay attention to the nutritional needs of this heavy feeder if you want to enjoy sweet, juicy watermelons throughout the summer.

The quality of fertilizer matters a lot in the case of watermelons. 

But there is no single best fertilizer for houseplants like watermelons because everything comes down to the condition of the soil. 

Finding the best fertilizer for watermelons can be challenging as there are so many options in the market, but we have created this buying guide to help you choose the best one. 



Best Fertilizer for Watermelons


Tomato and Vegetable Plant Food by Old Farmer’s Almanac – Best Overall Watermelon Fertilizer

Old Farmer’s Almanac is one of the well-known brands in the horticulture industry. Based on their vast experience, they offer some of the best products for home and professional gardeners.

Although this fertilizer is for tomatoes and vegetables, in my opinion, it can be used for any edible plant, including watermelons. 

This fertilizer is a simple solution to all the feeding requirements for indoor and outdoor plants growing in any geographic location. 

It’s derived from natural ingredients like feather meal, bone meal, soybean meal, and blood meal. 

A single bag can easily cover a crop area of 250 sq ft. The NPK ratio for this natural fertilizer is 8-4-8. It contains protein-based nutrition. 

This product targets long-term plant growth by using a combination of slow and quick-release nutrients. The special formula works with the natural ecosystem of the soil for better nutrient distribution. 

Just make sure the application is repeated every 6 or 8 weeks. 



  • OMRI listed and non-GMO ingredients 
  • High-quality proteins and nutrients for a healthy watermelon yield 
  • No harsh odor 
  • Can be applied to new or established watermelon crops
  • Free from manure or harmful chemicals 
  • Resealable bag 



  • Customers complained about overnight mold growth on the soil


Buy this product now on Amazon.


All-Purpose Water Soluble Plant Food by Jack’s Classic – Best Balanced Watermelon Fertilizer

JR Peter’s produces professional-grade plant food for your plants to help you enjoy the true essence of gardening with homegrown fruits and vegetables. 

They have a huge collection of water-soluble fertilizers for all types of houseplants. 

This fertilizer is a great balanced plant food that is rich in all three macronutrients. You can use this fertilizer for all types of outdoor vegetables and fruits, even the vining varieties like watermelons. 

The NPK is 20-20-20 and can be used in any growing stage of the watermelons. It contains several nutrients in chelated form for better performance and absorption of the fertilizer within the soil. 

As water-based fertilizer, this product is easily absorbed by the soil and roots, leading to a healthy crop. After diluting it in water, make sure you apply it directly to the soil near the base of the watermelon stems. 

This liquid plant food will deliver fast results to grow more fruit on the vines. 

Just mix 1 tablespoon of fertilizer in a gallon of water. Remember your watermelons should be fed every 7 or 14 days to produce the healthiest fruit. 



  • Filled with macronutrients and micronutrients
  • Gives a balanced dose of all essential nutrients 
  • Can be used for any foliage, vegetable, or fruiting plants
  • Designed to promote both root and stem development 
  • It contains an instruction pamphlet and a spoon



  • Contains urea which makes it unsuitable for hydroponic gardening
  • Might be too strong if used in high amount or on very young watermelons


You can buy this fertilizer by clicking here.


All-Purpose Fertilizer by FoxFarm – Best Organic Watermelon Fertilizer

I always recommend my fellow gardeners to buy organic plant food for their homegrown fruits or vegetables. 

You should go for the one that is rich in soil microbes that will reestablish the soil structure in the long term. 

Having healthy soil is extremely important for vining plants like watermelons that grow near the soil.

This particular Happy Frog fertilizer is not only organic but also has soil microbes; therefore, it’s our top recommendation for organic gardening of watermelons. 

These microbes will also speed up the nutrient uptake. 

The NPK ratio is 6-4-5; this means it has a high ratio of the two most important nutrients for initial watermelon growth – nitrogen and potassium. This is an OMRI-listed fertilizer for organic use. 

The nitrogen in this fertilizer will help you in growing a strong root system for your watermelon crop. 

This is a dry fertilizer and is sprinkled directly onto the soil. Since it’s an all-purpose fertilizer, you can also utilize it for other houseplants growing in your garden. 



  • A versatile fertilizer suitable for annuals, perennials, vegetables, and fruits
  • Ready to use product
  • Created using soil microbes, Mycorrhizal fungi, and beneficial nutrients
  • Top choice for organic production of watermelons
  • Can be used for new, container, in-ground, row, and established plants
  • Mild nutrient ratio to eliminate the risk of root burning



  • Does not dissolve in water


Click here to learn more about this fertilizer. 


Shake ‘n Feed Tomato, Fruit and Vegetables by Miracle-Gro – Best Continuous Release Watermelon Fertilizer

Watermelons are heavy feeders and need lots of food throughout their growth. For this reason, gardeners growing huge watermelon crops prefer to use a continuous-release type of fertilizers.

These ensure a steady supply of nutrients in the soil for several months.  The Shake’ n Feed is the go-to fertilizer for many fruit and vegetable gardeners. 

It contains NPK ratios of 10-5-15. 

It has additional calcium to fight calcium deficiency and strengthen the cell wall. This extra calcium plays an important role in the quality of the watermelons. 

This plant food indirectly feeds the houseplants by feeding microbes within the soil. 

Miracle-Gro has included natural ingredients for feeding microbes, namely earthworm castings, kelp, bone meal, and feather meal. 

Another benefit of this fertilizer is the easy instructions because all the detailed application rates are printed on the bottle. 

The microbes also improve the water distribution within the soil, which in return improves nutrient uptake. 

The nutrients are guaranteed to last for up to 3 months.  Remember, this fertilizer should be applied dry without diluting in water. But to start feeding, you must add water afterward.

Always avoid spreading or piling the fertilizer too close to the main stem. 



  • Can be used for container or in-ground watermelons
  • Designed to provide nourishment for the plants above and below the soil
  • Improves the taste and quality of watermelons with extra calcium 
  • It has a money-back guarantee 
  • Easy storage and application 
  • Increases fruit production 



  • Might kill young plants
  • The seal can break during shipping
  • Improper mixing can lead to fungus or mold growth on the soil surface


Take a good look at this amazing fertilizer here.


Flower and Vegetable Plant Food by Osmocote – Best Smart Release Watermelon Fertilizer 

The only way to produce a healthy watermelon crop is to have a strong and vigorous root system. This fertilizer is a nutrient-rich formula that targets both root and top growth. 

In fact, most professional gardeners believe it is a must-have for vegetable and fruit growers. 

It’s a complete fertilizer with an NPK of 14-14-14. It contains boron which is essential for developing the sweet flavor of watermelons. 

Osmocote has developed a unique resin coating; all the nutrients are enclosed in this coating. They are released only when required to prevent burns and have better control over plant feeding. 

The coating can react to low soil temperatures as well, which makes it great for fertilizing crops in the early growth stages. 

Sprinkle the granules in the soil, mix them well and add water to activate feeding. The nutrients are activated by water or warm temperature.

I have noticed a drastic change in the flavor of watermelons after using this fertilizer. 

The most notable feature of this fertilizer is the feeding time because a single feed can last for four months. Hence, you won’t have to fret about heavy feeders like watermelons. 

However, the biggest drawback of this product is that it’s not organic. So if you are more into organic gardening, this fertilizer might not be the best choice for you. 



  • A good source of nutrition for other vegetables and fruits in your garden 
  • Does not cause burns if used in compliance with instructions
  • Single feed lasts for four months 
  • Good for annual and perennial varieties 
  • Long shelf life 



  • The shells remain in the soil, which can result in soil contamination 
  • Has a weird smell
  • Poor packaging 


If you’re curious about this product, tap this link and learn more about it.


Edibles Plant Nutrition by Miracle-Gro – Best for Budget Watermelon Fertilizer

Most gardeners prefer plant foods designed for edible plants to feed their fruits and vegetables. Without a doubt, these fertilizers are not toxic and are safe to use for humans and pets. 

While searching for watermelon fertilizers, we came across this Miracle-Gro fertilizer for Edibles which is not only organic but also produces fast results. 

It’s certified by OMRI for the organic production of edible plants like watermelons. The NPK is 7-6-9. 

It’s eco-friendly because the bottle is created using recycled plastic and can be recycled once empty.

According to Miracle-Gro, your fruit crop will start showing results within seven days, which is great if you want an instant boost of nutrition for the watermelons. 

It also increases the fruit size compared to unfed watermelon crops. 

This fertilizer is easy to apply because all you have to do is sprinkle the fertilizer and mix it well in the soil. Maintain adequate moisture within the soil by watering the watermelons regularly. 



  • Organic fertilizer for all types of edibles
  • Shows results in just a week
  • Can be used for other heavy feeders like tomatoes
  • A single bottle can feed 220 sq ft 
  • Does not require precise measurements or mixing in water
  • For in-ground or container fruits and vegetables
  • Feeding instructions are printed on the bottle for convenience 



  • Not for hydroponics 
  • Dogs are attracted to the soil after using this fertilizer 
  • Can grow mold on the soil when used indoor
  • Not designed to dissolve in water


It’s best to read more of this fertilizer here.


Grow Big Liquid Plant Food by FoxFarm – Best Liquid Watermelon Fertilizer

This special formula is designed for the vegetative growth of vining plants such as watermelons. It improves the overall plant structure to produce big, juicy watermelons. 

The fertilizer analysis of this product is 6-4-4. But it also has decent amounts of chelated zinc, iron, copper, and manganese. 

This liquid plant food is created with low soil pH to make sure the nutrients are available for a long period, and the solution stays fresh if stored for too long.

This plant brew contains Norwegian kelp and earthworm castings. Follow the 2 teaspoons per gallon of water dilution rate before feeding it to the plants. 

The earthworm castings in this fertilizer will not only contribute to plant growth but improve aeration, disease/pest resistance, and water retention. 

For maximum results, FoxFarm recommends reapplying the fertilizer every week. 



  • Results in abundant fruit growth 
  • Fast-acting liquid fertilizer 
  • Designed at an optimum pH to keep the concentrate fresh for several years
  • Easy to use on outdoor and indoor plants
  • Contains earthworm castings to feed the living organisms in the soil  
  • Works as soil or foliar feeding 
  • Can be used in a hydroponic system 



  • Not for organic gardening since it’s a synthetic fertilizer 
  • Chunks of material in the liquid that do not dissolve 
  • The bottle can leak during shipping 

Learn more about this product here


Tomato and Vegetable Granular Plant Food by Burpee – Best Granular Watermelon Fertilizer 

This granular fertilizer is formulated for instant as well as long-term feeding. Some of the nutrients are released instantly, while others are released slowly over a period of 3 months. 

It’s filled with nutrients and certain soil microbes that contribute to crop health throughout the growth cycle of the watermelons.

I would highly recommend it for young watermelon or seedlings as the NPK ratio of 3-6-4 is ideal for their growing needs. The root system will also grow strong and robust with this plant food.

Continuous application can improve the taste and quality of the watermelons growing in your backyard. 



  • Fulfills the long term nutritional needs of watermelons 
  • Can be used for other edible houseplants, including vegetables and herbs 
  • Easy to apply in granular form 
  • Contains minor nutrients like calcium 
  • Certified by OMRI for organic gardening 
  • Targets root development 



  • Cannot be mixed with water 

Don’t forget to view the product here.


All-Purpose Granular Plant Food by Jobe’s – Best Multipurpose Watermelon Fertilizer

The reason we have classified this fertilizer as multipurpose is that in addition to providing the essential plant nutrients, this fertilizer performs three other duties. 

It enhances resistance against disease/pests, improves tolerance against drought, and manages soil conditions for better root and plant growth.

It’s enhanced with Biozome, which is a special ingredient in Jobe’s fertilizers. It’s a rich blend of microorganisms. 

All three macronutrients are present in equal ratios, i.e., 4-4-4. The active ingredients in this fertilizer are archaea, bacteria, and endomycorrhyzae. 

These ingredients also increase the root mass, meaning your plants will have a robust root system. 

This is a fast-acting fertilizer because the special microorganisms break down the nutrients fast. 

The bag for this fertilizer is also designed for easy pouring, so you do not waste any product while feeding your plants. 



  • Contains the special Biozome by Jobe’s
  • The organisms speed up the nutrient breakdown 
  • OMRI listed with zero chemicals 
  • Easy pour bag that can be resealed
  • Turns your plant green with lots of fruit growth 
  • Continuous use will recover the natural ecosystem of the soil 
  • Environment friendly 
  • Can be safely used around pets or kids



  • Has a strong odor 
  • Causes fungus and worm growth 
  • Pets like dogs might be attracted to the soil because of the strong smell

Learn about this wonderful product here.


Watermelon Fertilizer Buying Guide


Granular Fertilizer

You can use granular fertilizers as side-dress, broadcast, or band. They are also cheaper if you buy them in bulk. This can be a big advantage for growers with large watermelon crops. 

They are easier to store, and the only precaution is to keep them in a dry place away from direct sunlight. 

To prevent the foliage from burning, do not let any granular residue fertilizer sit on the surface of the leaves. Use a garden hose to wash the excess fertilizer from the leaves. 

Winner: Tomato and Vegetable Granular Plant Food by Burpee


Liquid Fertilizers

They can easily cover large areas compared to any other type of fertilizer. You can also blend them with other products like crop protection products or supplements. 

Liquid plant food ensures equal distribution because the soil is uniformly saturated with the fertilizer. 

Winner: Grow Big Liquid Plant Food by FoxFarm


Fertilizing Watermelons

The fertilizer type and rate for watermelon depend on two factors; the current nutrient level of soil and the growth stage of the watermelons. 

Therefore, the first step in preparing a fertilization schedule for watermelons should be testing the soil for nutrients and pH. 

Generally, your homegrown watermelon needs a nitrogen fertilizer in the beginning, but you should switch to phosphorus or potassium-based fertilizer once it enters the flowering stage.

Once the vines start growing, add a nitrogen-based or seaweed fertilizer to the soil. Never skip feeding the watermelons once the fruit starts setting because that can hinder fruit development. 

It’s crucial to understand that watermelons need extra nutrition during the fruiting stage. 

If you are confused about the NPK ratios, I would recommend opting for a complete, balanced fertilizer throughout all growth stages. 

A tasteless watermelon crop is often linked to boron deficiency. This element is responsible for the flavor and sweetness of the watermelons. 

Watermelons should be fertilized at the following stages:

  • Before planting the seeds indoors, this is known as the base fertilizer
  • Before transplanting the young seedlings to the outdoor garden, this is known as the seedling fertilizer
  • When the vines start spreading 
  • When the melon fruit starts setting 

The soil pH and drainage also impact the availability of nutrients within the soil. Therefore, it is important to grow watermelons in soil that suits their growing habits. 

The best soil pH for this plant is between 6 and 6.5

The choice between fast and slow-release fertilizer entirely depends on the plant requirements. 

If your watermelons need an instant boost or you missed the fertilization, you can apply an instant/fast release fertilizer; otherwise, slow-release fertilizers are the best choice. 


Tips for Watermelon Fertilization

  • For the slow addition of nitrogen, you should mulch the soil around the watermelons. Mulching will also discourage weed growth and improve moisture retention. 
  • To minimize any chemical burns (like nitrogen), it’s best to mix the granular fertilizer in the top 6 inches of the soil surface. 
  • Watering after fertilization is the most critical step because it will aid the roots in absorbing the nutrients supplied by the fertilizer. 
  • Once the vines start producing fruits, avoid fertilizing with a nitrogen-rich fertilizer. Otherwise, your plant will have more leaves and less fruit. 
  • To increase the sweetness of your watermelons, feed them with plant food that contains boron. You can also directly add boron by diluting it in water.
  • Mix 1 tablespoon of boron in 1 gallon of water to create a boron mixture. This mixture can be either sprayed on the leaves or applied to the soil near the plant base. 
  • Most growers prefer a granular fertilizer for the initial feeding and then shift to a liquid fertilizer for the remaining applications. 
  • Mix magnesium sulfate in the soil to improve fertility.
  • If the leaves start yellowing in the middle of the growing season, apply a liquid fertilizer (such as seaweed) to fix them. 
  • There is no fixed feeding time for watermelon crops, but you can add plant nutrition if your soil test indicates a lack of nutrients. Fertilizers can also be added based on the growing stage. 
  • To grow more watermelons, focus on feeding the female flowers. These flowers are bigger than the male ones.



Understand the nutrient ratios and ingredients in the fertilizer before adding it to the watermelon crop. This reduces the chances of over or under-feeding nutrients. 

Read the packaging label carefully to find out the NPK ratio of the chosen fertilizer. 

The nitrogen will help in producing lush green vines, whereas potassium and phosphorus help in melon production. 

Now you know everything about feeding watermelons, choose the best fertilizer for watermelons from this guide and start feeding!