Best Fertilizer for watermelon growing in a field

The 5 Best Fertilizers For Growing Amazing Watermelon

Do you want to grow the best watermelons in your neighborhood?

Growing a healthy, vibrant watermelon is no easy task. You have to take into account the soil quality, sunlight exposure, and even temperature in order to get your plants just right. But did you know that choosing the right fertilizer can make or break your harvest? In this article, we’ll explore different types of fertilizers and let you know which ones we think are the best fertilizers for growing delicious watermelons!

Our Top Pick –Jobe’s Organics Fruit & Citrus Spikes

These set-it and forget it spikes from Jobe’s Organics are the perfect all-in-one solution for your watermelon crops. Both OMRI listed for organic gardening by the USDA and Certified Organic, you can feel good about putting these near your edibles.

Just place them in the ground and watch as the pre-measured and time-released organic fertilizers provide food and nourishment to both the roots and leaves of your plants. Each spike provides a steady stream of nutrients and other naturally occurring microorganisms that result in larger, more delicious fruit.

These spikes also contain Jobe’s Biozome, a proprietary microorganism that aggressively breaks down material for faster results. This fertilizer not only helps support the nutrient needs of your watermelon, but also improves soil conditions, helps with disease resistance, insects, and drought. It is also available in a granular form if you prefer.

Best Fertilizers for Watermelon

Osmocote Smart-Release Plant Food Flower & Vegetable

The Osmocote Smart-Release Plant Food for flowers and vegetables is a must-have for vegetable gardeners. Made with controlled-release technology, this fertilizer releases nutrients slowly and according to the plant’s needs. This technology, paired with the fact that it feeds for up to 4 full months, makes for a more efficient and effective way of growing your watermelons.

It promotes vigorous top-growth and strong root development so in addition to being one of the best fertilizers for watermelon, is also ideal for other fruits, vegetables, and even perennials.

Dr. Earth Premium Gold All Purpose Fertilizer

Organic gardeners rave about the products made by Dr. Earth, and their Premium Gold All Purpose Fertilizer is no exception.

This fertilizer is made from organic materials that are safe for both people and pets, and is even is a great product for those doing hydroponics in addition to traditional soil growing. While it doesn’t have the controlled-release technology of the Osmocote, it does provide a steady stream of nutrients, making it one of the best fertilizers for watermelon if you are looking for instant nutrient delivery.

This 100% organic and natural, hand-crafted blend has added microbes and is ideal for providing balanced and fast nutrition for all vegetables, flowers, bedding plants, potted plants, all trees, shrubs, annuals, and perennials.

J R Peters Jack’s Classic All Purpose Fertilizer

Jack’s Classic 20-20-20 All Purpose Fertilizer from J. R. Peters is an excellent choice if you are looking for a water-soluble fertilizer to deliver essential nutrients to both the roots and the leaves of your watermelons.

This fertilizer contains an even mix of all three major plant food elements: nitrogen, phosphorus, and potassium (otherwise known as macro-nutrients), making it great for all types of plants including your prized watermelons! And the best part? It bursts into action within minutes after application, so you don’t have to worry about the fertilizers burning the roots of your precious watermelon plants.

Triple 10 All-Purpose Liquid Fertilizer

Triple 10 All-Purpose fertilizer is a liquid fertilizer, bursting with nutrients to help your watermelons thrive.

This nitrogen and phosphorous fertilizer contains high levels of nitrogen-rich amino acids for explosive root growth and phosphoric acid, which helps to release phosphorus – an essential element for growing healthy watermelons. It also includes potassium hydroxide, which promotes photosynthesis and aids in the overall health of your fruits and vegetables.

While this fertilizer does not contain trace minerals like iron, manganese, copper, and zinc, it does provide all the macro-nutrients you need to grow beautiful watermelons.

Simply add 1-2 oz. per gallon of water and apply every two weeks.

What Fertilizers Should Be Used on Watermelon

When deciding which fertilizers are the best for watermelon, there are several factors that you need to take into account.

Your soil type will play a big role when it comes to watermelon growth. If you have a great amount of clay in the soil, it will be a lot harder for your plants to soak up nutrients and grow. This is because clay holds water really well, but doesn’t allow anything else to pass through it. To solve this problem, you should probably choose a fertilizer that comes from either slow or continuous-release formulas. Another issue could be soil with depleted nutrients. Getting your soil tested is always recommended before adding any type of fertilizer to your watermelon plants. Most universities offer soil testing for free, so be sure to check on that option first!

The type of watermelon you are growing will also make a difference when choosing the best fertilizers for growing watermelons. For example, mini or baby melons need a full day of sunlight. This is because baby melons tend to grow more rapidly, and need a lot more nutrients in order to thrive properly. Let’s take a look at a few of these factors in detail.

Granular vs. Liquid Fertilizers

Fertilizers typically come in two different forms. Granular fertilizers are dry and will come in a bag or box and can be scattered around the soil. Liquid fertilizers, on the other hand, typically come in a bottle and will either be diluted with water or poured directly onto the soil, depending on the product instructions.

Both fertilizers have their advantages. Liquid fertilizer is typically easier to apply and will provide the necessary nutrients for your watermelon plants in a matter of seconds. However, liquid fertilizers will not feed microbes that live in the soil and help break down natural ingredients into nutrients that feed the watermelon plants.

Granular fertilizers often provide microbes as well as nutrients and can be released into the soil more gradually than liquid fertilizers. Granular fertilizers provide a slow and continuous feeding over time.

Reading Fertilizer Numbers

Your fertilizer will be labeled with three numbers. These numbers indicate the percentage of nutrients that are inside the product. This is also called the N-P-K ratio.

The first number is always nitrogen, which is a key ingredient for healthy plant growth. Your plants use nitrogen as a major building block in order to produce leaves and fruit. The second number is always phosphorus, which works hand-in-hand with potassium (the third number) in order to support the growth of healthy watermelons.

Best Fertilizer N-P-K Ratio for Watermelon

The best N-P-K ratio for watermelon should be around 28% nitrogen. Look for a fertilizer that has this number between 25 and 32% nitrogen content. Anything higher than 32 will probably do more harm than good.

Phosphorus should be around 8% or lower. When you look at phosphorus numbers on the fertilizer, they will usually have a decimal point, so be sure to pay attention to that detail.

Potassium is important for watermelon plants because it helps the fruit develop sugar and sweetness. Potassium also helps support root development in order to support healthy plant growth. Therefore, most fertilizer packets for watermelon will have a potassium number of around 0.5%.

Other Important Watermelon Fertilizer Ingredients

Besides nitrogen, phosphorus, and potassium, other nutrients are also important when it comes to growing healthy watermelons. Calcium is needed in order to give the plant structure and cell strength. This helps the plant grow sturdier, which makes it less likely to collapse during heavy rain or wind.

Secondly, magnesium is needed by the watermelon plants in order to support photosynthesis. Photosynthesis is important because it allows your plants to produce sugars that are used for energy and cellular respiration in order to make your plants grow and produce fruit.

Thirdly, sulfur is important for root growth and is needed in order to support the production of amino acids. Amino acids, such as glutamine and arginine, contribute to strong plant cells.

Zinc is also a great fertilizer ingredient because it helps your plants maintain their structure during periods of high temperatures and drought. It also helps the plant take in water, so it is important during periods of heat or dryness.

Finally, boron strengthens cell walls and root structure. Boron also assists with nitrogen metabolism inside the plant cells for cellular respiration.

When is the best time to fertilize Watermelon?

Watermelon should be fertilized every 4 to 6 weeks. Fertilizing more frequently can cause damage to the plant.

You should also fertilize your watermelon plants during flowering and right before fruit begins to grow. This is because these stages are crucial for producing tasty, delicious fruit.

Each time you fertilize, give your plants a small amount of nitrogen and potassium, and then they will only need the phosphorus once every 2 or 3 months.

Fertilizing Watermelon at Planting

When you first plant your watermelon seedlings, you should use a liquid fertilizer or fish emulsion, depending on the instructions. This is because liquid fertilizers are easier to absorb by the plant when they are young and have smaller root systems.

Liquid fertilizers sometimes contain urea, which is not good for watermelons. However, some concentrations of nitrogen can be beneficial for growing healthy plants.

Use Boron for Sweeter Fruits

Boron is an essential nutrient for growing juicy and sweet watermelon fruit. Adding boron can help boost the amount of sugar in your fruits and vegetables by increasing the carbohydrate content of your plants.

You can buy boron as a powder or as a foliar spray, and you can even make your own using borax from the grocery store.

Watermelons should be fertilized about one week before they flower in order to boost sugar levels in the fruit. It is also important that they are not over-fertilized, which can cause leaves to turn yellow and damage the fruit.

When your watermelon plants are flowering, you should stop fertilizing them entirely. You should also stop fertilizing once your fruits begin to grow because too much nitrogen in that stage will stunt their growth.

Methods to Determine Ripeness

Now that you have used the best fertilizer for your watermelons and have big green fruits in your garden, how do you know when to pick them?

There are several factors that can help you determine if your watermelon is ready to pick. Look at the tendrils on the stem of your watermelon. They should have begun to dry and brown. Also, look for a yellow spot that has formed on the bottom or opposite end of the vine. This is an area where the fruit was resting on the ground while it was growing, and the spot will help you determine if your watermelon is ready to pick.

Frequently Asked Questions

Why are my watermelon leaves turning yellow?

Yellow leaves on a watermelon plant are an indication of nitrogen deficiency. This can be fixed by adding fertilizer.

Why are my watermelon fruits splitting?

Splitting is caused by high temperatures, over-watering, or an abundant nitrogen supply in the fruit when it was developing. To prevent splitting, make sure you stop fertilizing once the plant has fruited.

How do I increase the yield of my Watermelon plant?

The size of your watermelons can be increased by adding more nitrogen to the soil. You should also space plants further apart so there is more room for each melon to grow and develop. Plants that are planted too closely will compete for both nutrients and water, reducing your yield.

How many Watermelon fruits do you get per plant?

One watermelon plant will typically yield 2-4 fruits, but smaller varieties may produce up to 8.


With so many different types of fertilizer out there, it can be hard to know which is the best for watermelon. Hopefully, this article has helped you understand what specific nutrients your watermelons need and helped you to find the perfect fertilizer for your garden!