The 5 Best Fertilizers for Watermelon

Not all fertilizers are created equal. The difference between the best fertilizers out there and average fertilizers is drastic. It can mean the difference between juicy, sweet watermelons and bland, pale watermelons.

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Set yourself up for success when you are growing watermelon by buying the best fertilizer possible. Many fertilizers do not have the proper nutrient ratios or use poor ingredients. Watermelon are not difficult to grow with the proper nutrients and watering. Keep reading below for the fertilizers that we recommend and also a care guide.

Here are the best fertilizers for watermelon that we recommend.

Comparing Our Top 3 Recommendations for Watermelon Fertilizers

Healthy watermelon

The Best Watermelon Fertilizers

These are the best fertilizers for watermelon. They use quality ingredients and are much better than the other fertilizers on the market. Please keep reading below to learn more about each one. 

Best Fertilizers for Watermelon

Osmocote Smart-Release Plant Food Flower & Vegetable is an excellent choice for watermelon in all of its stages of its life cycle. Osmocote has developed a special granule coating. This smart-release granule permits water to enter and dissolve the encapsulated nutrients. The nutrients are then slowly released over an extended period of time as temperatures change and as more water is applied. More nutrient is released during warmer growth periods. This fertilizer will help you successfully grow juicy, flavorful watermelon. Furthermore, because of its balanced N-P-K ratio, it is a great everyday fertilizer for many other plants and vegetables as well.

As stated above, mix the granules into the soil around the stem of your watermelon. Make sure to water well after application and don’t let the granules touch the plant itself.

Watermelon growers can feel great about using Dr Earth Premium Gold All Purpose Fertilizer because it’s made from organic materials that are safe for both people and pets. The formula is specifically crafted to grow healthier vegetable and fruit. It is perfect for establishing your watermelon and also as it continues to mature. This fertilizer contains a blend of humic acids, carbohydrates, and trace elements and minerals that help to create a better soil quality and nourish plants from the roots up. It contains no GMOs and no chicken waste. Watermelon treated with this fertilizer will develop healthy vines and ultimately full, rich watermelons.

Mix the granules into the soil of the watermelon. Scatter it around the stem and make sure to water it in well. This will allow it to be absorbed into the soil and prevent it from being blown away by the wind. Make sure that the granules do not come into contact with the plant. This can cause plant and leaf burn.

J R Peters Jacks Classic All Purpose Fertilizer is an excellent choice for a water soluble fertilizer. This fertilizer contains a balance of phosphorus, potassium, and nitrogen that works well for both the immature and mature stages of watermelon growth. The water soluble formula sinks into the soil, nourishing the roots to create healthier, stronger watermelon.

Tip for application: When you are applying water soluble fertilizer, mix the fertilizer and then pour it right at the base of the main stem of your watermelon.

Triple 10 All Purpose Liquid Fertilizer contains a balance of nutrients, amino acids, and seaweed extract that help to elevate soil quality and nourish a range of plants, including watermelon. This fertilizer formula is specifically designed to help plants grow larger and become healthier, even during later growth stages. The fertilizer is simple to measure out and pour.

Similar to above, when you are applying the fertilizer, pour it right at the base of the main stem of your watermelon

Shultz All Purpose Plant Food Plus is the perfect choice for watermelons, particularly once the watermelons begin to set. It has a higher phosphorous content and lower nitrogen so as to not encourage excessive foliage growth. This liquid fertilizer is easy to measure and apply. Adding a few drops of the fertilizer to the soil at the base of the main stem is enough to nourish your watermelons for an extended period of time. Nutrients will be released into the soil, and thus to the roots, every time it rains or the watermelon is watered. Gardeners will find that watermelon treated with this formula experience more juicy and sweet watermelon production.

Can You Grow Watermelon at Home? Yes!

Who can’t resist the taste of a sweet, juicy watermelon in the summer? Every gardener should have a go at planting watermelons. They are easy to grow, fun to raise, and rewarding to eat.

What Type of Watermelon Should You Grow?

There are many different types of watermelons. The varieties that we recommend are:

How to Grow Watermelons

Watermelons need warm soil for the seeds to have the best chance at germinating. It is best if the soil can be warmer than 70 degrees Fahrenheit.

Sow the seeds at roughly a depth of 1 inch and keep the soil well watered until germination occurs. To help the germination process in cooler areas, you can start the germination process indoor. Sow the watermelon seeds roughly ½ inch deep and place it in a south-facing window or under grow lights. Keep the area warm or use a seedling heat mat. Try to keep the soil at roughly 80 degrees fahrenheit. Once it has germinated, transplant it out doors.

Best Fertilizer N-P-K Ratio for Watermelon

As you may know, all plants need macronutrients and micronutrients. N-P-K are the primary macronutrients, so you should always be checking fertilizer labels to find the N-P-K ratio.

Watermelons do best with higher nitrogen fertilizers when they are young and as a fertilizer that has more potassium and phosphorus for melon production.  Using high nitrogen fertilizers after the melons are setting can result in excessive foliage growth rather than melon development. This will nourish the vine rather than the fruit! An N-P-K ratio of roughly 1-1-1 (such as 10-10-10 or 14-14-14) can be used throughout the lifecycle of your watermelon. Just make sure that if you are using a fertilizer with higher nitrogen components that you switch to one that is more balanced when your melon set.

Fertilize your watermelon three times throughout its life cycle. Once before are first planting the seed or transplanting your seedling. Once when the vines begin to ramble. And a third time when the watermelons are set.

If you are using a granular fertilizer, make sure the fertilizer does not touch the leaves. The leaves are sensitive and can be damaged by contacting the fertilizer. After application, make sure to water well so the roots can take in the nutrients.

Where to Plant Watermelon

Watermelon vines can grow quite long. Sometimes the vines can reach up to 15-20 feet long. Plant in an area where there is a lot of open space. It is best if you can add some organic matter such as compost to the area. Sow about 8 seeds or germinated seeds in a hill at about a depth of 1 inch. Once the seeds start taking off, leave only the best 3 seedlings.

Make sure that you watch the soil and remove any weeds. You can also prevent weeds by adding a layer of mulch.

Water Only When Soil is Dry

Because watermelons have deep roots, frequent watering is not necessary. Oftentimes, rain itself is enough. Watering is only necessary if the weather turns dry for a long period.

Another tip is to try to withhold even more water when you watermelons start to mature. This will help your watermelon become even sweeter.

Use Boron for Sweeter Watermelons

When your watermelon’s vines begin to ramble, give your watermelons some boron. You can dissolve 1 tablespoon of Borax in 1 gallon of water and spray the base of the plant.

Methods to Determine Ripeness

It can be difficult to know when a watermelon is ripe. Use the seed’s harvest time as a general guideline. Watch the tendril. The tendril is the leave closes to the melon stem. When it turns brown and dries, you know that your watermelon is almost ripe. However, this isn’t always accurate as sometimes you need to wait a couple days after it falls off.

You can also tap your watermelon. You want a deep and hollow sounding thud. This suggests that the inners are softening up and ready for eating.

Another clue of ripeness is to look at the bottom of the watermelon. As the watermelon ripens, it should turn from a white to a yellow color.

Bottom Line

Again, I recommend buying the Osmocote’s fertilizer. Don’t make the mistake of buying any average fertilizer at your local gardening store. Many of them will simply not produce the same results. You cannot go wrong with any of the fertilizers above. 

If you want to read our more comprehensive guide for growing watermelon, you can do so here. 

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About the author: Carley Miller is a horticultural expert at TheGreenPinky. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.

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