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7 Picks for Best Fertilizer for Watermelons

No fruit announces summertime better than watermelon. To try growing delicious, homegrown watermelons, you must know how to care for them as they grow.

A big part of your watermelon success will depend on ensuring your watermelon plants have all the nutrients they need to produce large, healthy fruit. Using fertilizer is a sure way to feed your garden and boost its growth.

I’ve listed the best six fertilizers for watermelons. Keep reading to learn more!

A large, healthy watermelon.

Our Top Picks

Best All-Purpose:
Hoss Complete Organic Fertilizer

Runner Up All-Purpose:
Dr. Earth Premium Gold All Purpose Fertilizer

Or, if you want to target different growing stages with the ideal fertilizer:

Best Early Season (plant growth):
Dr. Earth Natural Wonder Fruit Tree Fertilizer

Best Late Season (melon growth):
Dr. Earth Flower Girl Bud and Bloom Booster

What Do Watermelons Need in a Fertilizer?

Before you choose a fertilizer for watermelon, it’s essential to understand what nutrients watermelons need. As a watermelon plant begins to develop from a seedling, they need a good source of nitrogen.

Nitrogen helps encourage vine growth and leaf production, which is important for providing a shady environment for developing fruit.

Person uncovering watermelon. The best fertilizer for watermelons promotes healthy leaf growth.

Nitrogen-heavy fertilizers should be applied until the vines begin to produce fruit. Using lots of nitrogen after the vine flowers could leave you with all leaves and no fruit.

At that point, you can switch to an all-purpose fertilizer with a higher source of potassium and phosphorus. This will help create large, quality watermelons that taste delicious!

The Six Best Fertilizers for Watermelons

Best All-Purpose

Hoss Complete Organic Fertilizer with Calcium

Hoss Organic Fertilizer

Calcium is a big proponent of your plant’s strength. If a seedling grows too rapidly, it could become detrimental to the plant if there’s insufficient calcium. Calcium works to strengthen the cells and help the plant absorb all of the other nutrients contained in a fertilizer.

Hoss Complete Organic Fertilizer is the best watermelon fertilizer for administering calcium to the plant’s roots. This granular fertilizer contains 9% calcium, which helps your plants produce the healthiest watermelons. It also contains a good source of nitrogen to boost foliage production early in the season.

This product will feed your garden all season when applied to the soil surrounding the plants, and it only needs to be reapplied every four to six weeks. It’s one of the pricier fertilizer options, but this Hoss fertilizer is certified organic and domestically sourced.


  • Good source of calcium
  • Fewer applications than liquid fertilizer
  • Certified organic


  • Can be pricey

Runner Up All-Purpose

Dr. Earth Premium Gold

Dr. Earth 70857 1 lb MINIS Premium Gold All Purpose Fertilizer

Healthy plants start with healthy soil! That’s why Dr. Earth Premium Gold All Purpose Fertilizer makes the list. With their fertilizer, Dr. Earth prioritizes improving the soil, which will in turn promote growth for your watermelon plant.

This granular watermelon fertilizer contains a balanced source of all the important nutrients watermelons need. It also contains soil microbes, which work to provide watermelons with nutrients all season long.

As the microbes break down in the soil, they will slowly release nutrients to the roots as the plant needs them. This results in fewer applications needed and increased drought tolerance.

If you worry about where fertilizers are sourced from, you can rest assured with this choice. It’s only derived from domestically sourced fish, plants, and minerals. No toxic chemicals or ingredients are used.


  • Improves soil health
  • Made in the U.S.A.
  • Helps with drought tolerance
  • Fewer applications than liquid fertilizer


  • Strong smell

Best for Early Season

Dr. Earth Natural Wonder Fruit Tree Fertilizer

Dr. Earth 70656 1 lb 5-5-2 MINIS Natural Wonder Fruit Tree Fertilizer

The next fertilizer for watermelon I’ve chosen is Dr. Earth Natural Wonder Fruit Tree Fertilizer. It has all the perks of Dr. Earth’s Premium Gold Fertilizer, but this one is specifically tailored to early-season vine growth.

This granular fertilizer has an NPK ratio of 5-5-2, which means it has a great source of nitrogen. If you need some help with seedling growth at the beginning of the season, this fertilizer will help your watermelon plants produce hearty foliage.

While it’s labeled a fruit tree fertilizer, it’s made to stimulate the growth of any kind of vining fruits and fruit trees.

As all Dr. Earth products are, it’s certified organic and made in the U.S.A., so it’s an environmentally conscious purchase! To apply, simply mix into the soil under the watermelon plant’s dripline and water to activate.


  • Great source of nitrogen
  • Helps with fruit production
  • Certified organic
  • Made in the U.S.A.


  • Some reviewers had mold in their fertilizer upon arrival.

Best for Late Season

Dr. Earth Flower Girl Bud and Bloom Booster

Dr. Earth GL61100518430 Fertilizer & Soil 707P Organic 8 Bud & Bloom Fertilizer in Poly Bag, 4-Pound, 4 lb, Natural

Once your watermelon plant is fully mature and ready to reproduce, it reaches the flowering and fruiting stage. During this period, its nutritional needs change significantly.

When plants are gearing up to produce fruit, they do not need as much nitrogen. Instead, the fruiting and flowering process requires extra phosphorus.

To supply your watermelon with the necessary ingredients for a bountiful harvest, you’ll want to look for a fertilizer with less nitrogen and more phosphorus.

Adding Dr. Earth Flower Girl Bud and Bloom Booster to your melon patch creates the best soil composition of key minerals and helpful microbes to promote the growth of juicy watermelons.


  • Great source of nitrogen
  • Helps with fruit production
  • Certified organic
  • Made in the U.S.A.


  • Some reviewers had mold in their fertilizer upon arrival.

Espoma Garden-Tone Organic Vegetable Food

Espoma Organic Garden-Tone 3-4-4 Organic Fertilizer for Cool & Warm Season Vegetables and Herbs. Grow an Abundant Harvest of Nutritious and Flavorful Vegetables – 4 lb. Bag

Another excellent choice for the best watermelon fertilizer is Espoma Garden-Tone Organic Vegetable Food because of the abundance of nutrients it provides. This granular fertilizer has an NPK (Nitrogen Phosphorus Potassium) ratio of 3-4-4, so it’s great to use as your plants begin to produce fruit.

This Espoma fertilizer contains a good source of calcium, which helps the watermelon plant build strength and absorb all the other nutrients.

It also has added microbes, so as you add this fertilizer to your garden, you are simultaneously improving your soil health. Not to mention, it doesn’t contain any toxic chemicals and is completely safe to use!

To use this fertilizer, all you have to do is mix it into the top layer of soil surrounding your plant, then water it thoroughly. Espoma Garden-Tone will continue to feed your watermelons all season.


  • Certified organic
  • Improves soil health
  • Fewer applications than liquid fertilizer
  • Great for fruit production


  • Strong smell

Best Liquid Fertilizer

Neptune’s Harvest Fish Fertilizer 2-4-1

Neptune's Harvest Fish Fertilizer 2-4-1, Gallon

If you prefer using liquid fertilizer for watermelon growth, look no further than Neptune’s Harvest. Their fish fertilizer is an excellent way to instantly release nutrients to your watermelon plants.

Made from fresh North Atlantic fish, this fertilizer adds all the micro and macro nutrients found in fish, and guess what – your soil loves it, too! It’s an all-natural way to fertilize your garden.

Just watch your garden if you have pets that roam near it. They tend to be drawn to the smell of fish fertilizer, and you don’t want your furry friends to stomp out your plants.

To use this watermelon fertilizer, dilute one ounce of it in a gallon of water and apply it weekly. That’s more work than a granular fertilizer, but you’re guaranteed to consistently feed your watermelon plants.


  • Instantly feeds plants
  • Organic
  • Good for soil health


  • Frequent applications required
  • Pets can be attracted to smell

Jacks Classic 20-20-20 All-Purpose Fertilizer

J R Peters 52024 Jacks Classic No.1.5 20-20-20 All Purpose Fertilizer

Watermelons have very similar needs to other fruits and vegetables regarding fertilizer. That’s why there’s no harm in using an all-purpose fertilizer on your watermelon plants. It’s a cost-effective way to take care of your whole garden!

My choice for the best all-purpose fertilizer is Jacks’s Classic. Your watermelon plants will love it! It has a large NPK ratio of 20-20-20. While that can seem intimidating, it’s completely safe when used sparingly, and it’s a great source of nitrogen.

Jacks’s Classic All Purpose Fertilizer is applied by diluting it with water. Follow the instructions for the correct proportions, and use it biweekly on your plants early in the season. It’ll boost your watermelon plant foliage as you’ve never seen!

Once your watermelons start to produce fruit, switch to a watermelon fertilizer with a smaller percentage of nitrogen, so the plant can focus on growing fruit instead of leaves.


  • Versatile
  • Cost-friendly
  • Great source of nitrogen


  • Can overwhelm plants if used too much

Types of Watermelon Fertilizers


There are different types of watermelon fertilizers that you’ll run into. The first is liquid. Liquid fertilizers are typically mixed with a gallon of water to dilute the fertilizer, then applied to your garden. These types of fertilizers can be pricey, but they are fast-acting and can be applied directly to the plant.


Granular fertilizers are cost-friendly fertilizers that are applied to the soil surrounding your plants’ dripline (the reach of the foliage). They have a slower release, but they allow you to make fewer applications throughout the season. Granular fertilizers are also better for storing.

Person holding handful of granular fertilizer mix.

Organic v. Synthetic

As you shop fertilizers, you’ll notice some are labeled “organic”, while others are considered synthetic, or inorganic. Organic fertilizers are usually plant-based or made from some other natural material.

Synthetic fertilizers are composed of different chemicals, but they are usually more cost-friendly. Some prefer not to use these, as they could have a negative environmental impact.

Either type of fertilizer will give watermelons what they need in terms of nutrients. It just depends on how you choose to garden.

The Best Watermelon Fertilizers for Tasty Melons!

Closeup of a watermelon growing in a garden.

By using one of these fertilizers for watermelons, you’re setting your garden up for success. My top pick for the best watermelon fertilizer is Espoma Garden-Tone Organic Vegetable Food because of all the helpful nutrients it contains. Before you know it, you’ll have more watermelons than you know what to do with!

For more helpful content on growing watermelons, visit our Watermelon Plants page where you’ll find all kinds of tips on keeping your watermelon plants healthy this season.

Shopping for your garden can get overwhelming fast. So if you’re looking for advice on tools and supplies, then you’re in the right place!