10 Best Fertilizers for Watermelon to Grow Juicy, Sweet Fruit

I’ve found that specialized watermelon fertilizers like LEAVES AND SOUL Professional Liquid Melon Fertilizer (5-1-5) and Farmer’s Secret Fruit & Bloom Booster deliver exceptional results for sweet, juicy fruit. Liquid Power’s spray formula provides quick foliar feeding, while Pennington’s 20-10-20 water-soluble blend supports larger yields through balanced nutrition. For sustained growth, I recommend slow-release granular options or organic choices like FoxFarm Big Bloom with earthworm castings. The complete selection below reveals ideal timing and application methods.

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Notable Insights

• LEAVES AND SOUL Professional Liquid Melon Fertilizer offers specialized 5-1-5 nutrient ratio optimized for watermelon vine development and growth.
• Pennington Water Soluble 20-10-20 fertilizer provides quick nutrient absorption and supports larger watermelon yields through balanced nutrition.
• FoxFarm Big Bloom organic fertilizer contains earthworm castings and bat guano for gentle, natural nutrient support throughout growing seasons.
• Triple 10 liquid fertilizer combines balanced NPK with seaweed extract and amino acids to enhance fruit quality and sweetness.
• Slow-release 10-10-10 granular fertilizer delivers consistent nutrients for up to 8 weeks, promoting strong root development and plant health.

LEAVES AND SOUL Professional Liquid Melon Fertilizer (5-1-5 Concentrate, 8 oz)

LEAVES AND SOUL Professional Liquid Melon Fertilizer stands out as the ideal choice for gardeners who want a specialized, concentrated solution that delivers targeted nutrition specifically formulated for watermelon cultivation. This 8-ounce concentrate features a carefully balanced 5-1-5 nutrient ratio, providing maximum nitrogen for vigorous vine growth, moderate phosphorus for root development, and potassium for fruit quality. You’ll appreciate the liquid format’s convenience, as it mixes effortlessly with water and adapts to different growth stages. The premium ingredients guarantee your watermelon plants receive consistent nutrition from seedling to harvest, promoting healthy development and improved yields that satisfy both novice and experienced gardeners.

Best For: Gardeners seeking a specialized liquid fertilizer concentrate designed specifically for watermelon cultivation that provides targeted nutrition from seedling to harvest stage.

Pros:

• Specialized 5-1-5 nutrient ratio optimized specifically for watermelon growth with high nitrogen for vine development and potassium for fruit quality
• Convenient liquid concentrate format that mixes easily with water and adapts to different plant growth stages
• Premium quality ingredients that provide consistent nutrition and deliver improved yields for both beginner and experienced gardeners

Cons:

• Limited to 8-ounce size which may require frequent repurchasing for larger gardens or multiple growing seasons
• Specialized formulation restricts use primarily to melons rather than being a versatile all-purpose fertilizer
• Liquid concentrate requires proper mixing and storage compared to ready-to-use fertilizer options

Farmer’s Secret Fruit & Bloom Booster Fertilizer (16oz)

Watermelon growers seeking to maximize their late-season harvest will find exceptional value in Farmer’s Secret Fruit & Bloom Booster Fertilizer, a powerhouse solution that transforms struggling vines into productive fruit machines. This super concentrated formula strengthens root systems, which dramatically improves nutrient uptake during critical flowering and fruiting phases. You’ll appreciate the economical 16-ounce bottle that dilutes at just one teaspoon per two gallons, making each application cost-effective while delivering professional results. The fertilizer’s late summer and early fall timing perfectly aligns with watermelon development, providing essential nutrients when plants need them most. Simply dilute and apply every two to four weeks during regular watering sessions for ideal performance.

Best For: Watermelon growers and gardeners looking to boost late-season fruit production and flowering with a concentrated, economical fertilizer that strengthens root systems and improves nutrient uptake.

Pros:

• Highly concentrated formula provides exceptional value with dilution ratio of just 1 teaspoon per 2 gallons of water
• Specifically designed for late summer and early fall application when watermelons need critical nutrients for fruiting
• Easy application process that integrates seamlessly into regular watering routines every 2-4 weeks

Cons:

• Limited to late-season application timing, not suitable for early growth phases
• Requires careful dilution measurements to avoid over-concentration
• 16oz bottle size may not be sufficient for large-scale watermelon operations

PREMIUM Liquid Silica Plant Supplement – 8oz Watermelon Plants Fertilizer

Growing robust, stress-resistant watermelon plants becomes markedly easier when you incorporate PREMIUM Liquid Silica Plant Supplement into your fertilization routine. This concentrated 8oz formula strengthens cell walls, preventing stalk breakage while protecting leaves from environmental browning. The bio-available silica from organic acid chelation and plant extracts helps your watermelons resist heat, drought, and humidity stress effectively. You’ll notice thicker leaves and sturdier stems as the silica reinforces plant structure throughout growth phases. Whether you’re gardening in soil or hydroponics, this versatile supplement mixes easily at 1-1.5 teaspoons per gallon during vegetative growth, reducing to 1 teaspoon during bloom phase.

Best For: Watermelon growers seeking to strengthen plant structure, prevent stalk breakage, and improve stress resistance in both indoor and outdoor gardens.

Pros:

• Bio-available silica formula strengthens cell walls and prevents stalk breakage while protecting leaves from environmental browning
• Highly concentrated solution makes up to 45 gallons from just 8oz, offering excellent value and cost efficiency
• Versatile application methods including watering can, hose sprayer, and foliar spray, compatible with both soil and hydroponic systems

Cons:

• Specifically formulated for watermelons, limiting its use for diverse garden crops
• Requires different mixing ratios for various application methods, which may be confusing for beginners
• No mention of organic certification despite containing organic acid chelated ingredients

Liquid Power Watermelon Fertilizer Spray (8 oz)

Busy gardeners who need quick, effective nutrition for their watermelon plants will find this 8-ounce spray bottle delivers professional-grade results without the complexity of mixing concentrates. You’ll appreciate the ready-to-use formula that provides foliar feeding, allowing nutrients to absorb directly through leaves and stems for immediate plant response. This fertilizer spray promotes robust root development, vibrant foliage growth, and enhanced fruit quality through consistent nutrient delivery. Whether you’re growing watermelons in containers, raised beds, or traditional garden plots, this versatile product adapts to various growing environments. You can confidently use this spray to help stressed plants recover from transplant shock, heat damage, or drought conditions while maintaining ideal nutrition levels.

Best For: Busy gardeners growing watermelons in various environments who want a convenient, ready-to-use fertilizer that delivers quick results without the hassle of mixing concentrates.

Pros:

• Ready-to-use formula eliminates the need for measuring and mixing, making application quick and convenient
• Foliar feeding delivers nutrients directly through leaves for fast absorption and immediate plant response
• Versatile application works effectively in containers, raised beds, and traditional garden plots while helping plants recover from stress

Cons:

• 8-ounce size may require frequent repurchasing for larger watermelon gardens or multiple plants
• Higher cost per application compared to concentrated fertilizers that can be diluted
• Limited to watermelon-specific nutrition rather than being a general-purpose fertilizer for diverse crops

Liquid Power Watermelon Fertilizer – Professional Plant Food (8 oz)

Professional growers and dedicated home gardeners who demand maximum fruit quality will find their ideal solution in Gardenera’s LIQUID POWER Watermelon Fertilizer. This fast-acting concentrate delivers a balanced NPK formulation with organic acids, promoting vigorous vine growth and exceptional fruit development. You’ll appreciate its low pH of 1.69, which reveals essential micronutrients like iron, manganese, and zinc for peak plant health. The formula enhances moisture retention, improves drought tolerance, and supports your watermelons through every growth stage from transplant to harvest. You can use this versatile fertilizer in containers, greenhouses, or garden beds with simple mix-and-pour application for noticeably sweeter, larger watermelons.

Best For: Professional growers and dedicated home gardeners who want to maximize watermelon fruit quality, size, and sweetness through specialized nutrition designed specifically for watermelon plants.

Pros:

• Fast-acting liquid concentrate with balanced NPK formulation and organic acids that promotes vigorous vine growth and exceptional fruit development
• Low pH of 1.69 unlocks essential micronutrients like iron, manganese, and zinc for improved plant health, especially in alkaline soils
• Versatile application for containers, greenhouses, or garden beds with simple mix-and-pour method that delivers noticeable results in fruit size and sweetness within weeks

Cons:

• Specialized formulation may limit cost-effectiveness for gardeners growing diverse crops beyond watermelons and related varieties
• 8 oz container size may require frequent repurchasing for large-scale growing operations or extensive watermelon patches
• Very low pH of 1.69 requires careful handling and proper dilution to avoid potential plant damage from over-concentration

FoxFarm Big Bloom Plant Food Liquid Fertilizer Concentrate (Pint)

Watermelon enthusiasts seeking a gentle, organic approach to fertilization will find FoxFarm Big Bloom Plant Food an exceptional choice for enhancing fruit development and flavor intensity. This micro-brewed concentrate features earthworm castings and bat guano, delivering essential nutrients through natural ingredients that won’t harm your plants or soil. With its low NPK ratio of 0-0.5-0.7, you’ll provide gentle phosphorus and potassium support that promotes robust root development and intensifies the natural sweetness of your watermelons. The liquid concentrate mixes easily with water in your watering can, making application straightforward for both garden beds and container growing. You can use this organic fertilizer regularly throughout the growing season, confident that you’re supporting stronger flavors while maintaining soil health through chemical-free nutrition.

Best For: Watermelon growers and gardeners who want an organic, gentle fertilizer that enhances fruit flavor and sweetness while promoting healthy root development through natural ingredients.

Pros:

• Organic formula with earthworm castings and bat guano provides chemical-free nutrition that’s safe for regular use
• Low NPK ratio (0-0.5-0.7) offers gentle phosphorus and potassium support without risk of over-fertilization
• Easy-to-use liquid concentrate mixes simply with water and enhances natural fruit sweetness and flavor intensity

Cons:

• Very low nutrient concentration may require frequent applications for plants with high nutritional needs
• Limited nitrogen content (0%) means you’ll need additional fertilizers for plants requiring more nitrogen during growth phases
• Higher cost per nutrient unit compared to synthetic fertilizers due to organic ingredient sourcing

Triple 10 All Purpose Liquid Fertilizer 10-10-10 with Amino Acids & Seaweed Extract (32oz)

When you’re seeking a versatile fertilizer that supports watermelons throughout their entire growing cycle, Triple 10 All Purpose Liquid Fertilizer delivers balanced nutrition with valuable organic additives. This 10-10-10 NPK formula provides equal amounts of nitrogen, phosphorus, and potassium, ensuring your watermelon plants receive thorough nutrition from seedling to harvest. The added amino acids and seaweed extract enhance nutrient uptake, promoting stronger root development and improved fruit quality. You’ll appreciate the convenient 32-ounce concentrate that creates up to 32 gallons of fertilizer solution when mixed at the recommended 1-2 ounces per gallon ratio. Apply this liquid fertilizer every 1-2 weeks throughout the growing season for consistent results.

Best For: Gardeners growing watermelons or other fruits and vegetables who want a balanced, all-purpose liquid fertilizer with organic additives that works throughout the entire growing cycle.

Pros:

• Balanced 10-10-10 NPK ratio with beneficial amino acids and seaweed extract for enhanced nutrient uptake
• High concentrate formula makes up to 32 gallons of fertilizer, providing excellent value
• Easy-to-use squeeze bottle with precise measurement capabilities for accurate dosing

Cons:

• Requires regular applications every 1-2 weeks throughout the growing season
• May need supplementation with specialized fertilizers for plants with specific nutrient requirements
• Liquid format requires mixing and can be less convenient than granular fertilizers for large areas

10-10-10 All Purpose Plant Food – Liquid Fertilizer with Seaweed Kelp & Iron (8oz)

Balanced nutrition becomes essential for watermelon growers seeking consistent yields, vigorous growth, and healthy fruit development throughout the growing season. This 10-10-10 liquid fertilizer delivers equal parts nitrogen, phosphorus, and potassium, creating ideal conditions for watermelon vines to establish strong root systems and produce abundant foliage. You’ll appreciate the enhanced formula’s seaweed extract, which provides critical micronutrients and growth hormones that support flowering and fruit set. The 6% chelated iron prevents chlorosis across varying soil pH levels, ensuring your watermelon leaves maintain their vibrant green color throughout summer heat. This concentrate mixes easily with water, making application simple whether you’re hand-watering or using irrigation systems.

Best For: Watermelon growers and gardeners who want a balanced, all-purpose liquid fertilizer that supports strong root development, vigorous foliage growth, and healthy fruit production while preventing nutrient deficiencies.

Pros:

• Balanced 10-10-10 NPK formula with seaweed extract and chelated iron provides complete nutrition for watermelon growth from establishment through fruit development
• Easy-to-use liquid concentrate that mixes with water and works with both hand-watering and irrigation systems
• Contains 6% chelated iron that prevents chlorosis and maintains vibrant green foliage across varying soil pH levels

Cons:

• Small 8oz package size may require frequent reordering for large watermelon growing operations
• Some customers have reported initial packaging and sizing concerns that required seller intervention
• As a liquid concentrate, it requires proper storage conditions and mixing ratios for optimal effectiveness

10-10-10 Plant Fertilizer Slow Release (1/2 Quart)

Gardeners seeking a reliable, all-purpose solution for their watermelon crops will find exceptional value in 10-10-10 plant fertilizer slow release. This balanced granular formula delivers equal parts nitrogen, phosphorus, and potassium, providing thorough nutrition that supports strong root development, vigorous vine growth, and enhanced fruit production. The slow-release technology feeds your watermelon plants consistently for up to eight weeks, eliminating the need for frequent reapplication while ensuring steady nutrient availability throughout the growing season. You’ll appreciate the fine granules that distribute evenly across your garden beds, maximizing soil absorption and minimizing waste. Apply twice per season for peak results, watching your watermelon plants develop robust foliage and resilient root systems that translate into sweeter, juicier fruit.

Best For: Gardeners growing watermelons and other outdoor plants who want a convenient, balanced fertilizer that provides consistent nutrition for up to 8 weeks without frequent reapplication.

Pros:

• Slow-release formula feeds plants for up to 8 weeks, reducing the need for frequent applications
• Balanced 10-10-10 NPK ratio supports strong roots, vigorous growth, and enhanced fruit production
• Fine granules ensure even distribution and maximum soil absorption across garden beds

Cons:

• Higher price point compared to similar fertilizer products like Milorganite
• Limited package size at 1/2 quart may not be sufficient for larger garden areas
• May require verification of compatibility and application methods for specific plant types to achieve optimal results

Pennington Water Soluble All Purpose Plant Food 20-10-20 8/1.5lb

Watermelon growers seeking consistent, reliable nutrition throughout the growing season will find Pennington Water Soluble All Purpose Plant Food 20-10-20 delivers exceptional results for their crops. This balanced formula provides essential nutrients that promote larger, more bountiful watermelons compared to unfed plants, guaranteeing you’ll harvest sweet, juicy fruit. The water-soluble design allows for quick nutrient absorption, while the included measuring scoop guarantees precise application every time. You’ll appreciate the wide-mouth jar’s convenient design, which prevents messy spills during preparation, and the foam seal that keeps the formula fresh and free-flowing throughout the season.

Best For: Watermelon growers and gardeners seeking a reliable, balanced water-soluble fertilizer that promotes larger, more bountiful growth across all plant types including fruits, vegetables, and flowers.

Pros:

• Water-soluble formula allows for quick nutrient absorption and easy application
• Includes measuring scoop for precise application and wide-mouth jar design prevents messy spills
• Foam seal on lid maintains freshness and keeps formula dry and free-flowing throughout the season

Cons:

• Requires regular dilution and mixing before each application
• 1.5lb container size may not be sufficient for large-scale gardening operations
• Generic 20-10-20 formula may not address specific nutrient needs of particular plant varieties

Factors to Consider When Choosing Fertilizer for Watermelon

I’ll guide you through the essential factors that determine which fertilizer works best for your watermelon plants. Understanding NPK ratios, growth stage requirements, and application methods helps you match nutrients to your plants’ specific needs. You’ll also want to assess your soil’s pH levels and proper concentration rates to maximize fruit development and vine health.

NPK Ratio Requirements

When selecting the right fertilizer for your watermelon crop, understanding NPK ratios becomes essential for achieving ideal plant development and fruit production. I recommend starting with a 5-1-5 ratio during early growth stages, which promotes vigorous vine development and establishes strong root systems in your seedlings. As your plants shift to flowering and fruiting phases, I suggest switching to a balanced 10-10-10 formula that supports healthy flower formation while maintaining robust root development. For maximum fruit size and sweetness during the final maturation period, I prefer using fertilizers with higher potassium content, such as 20-10-20 ratios, which notably enhance fruit quality. Regular soil testing helps me determine when to adjust these ratios throughout the growing season.

Growth Stage Needs

Understanding these basic NPK ratios provides the foundation for timing your fertilizer applications correctly throughout your watermelon’s development cycle. During the seedling stage, I recommend using a balanced fertilizer like 5-1-5 to establish strong root systems and encourage healthy initial growth. As your plants enter the vegetative phase, you’ll want to increase nitrogen levels to promote vigorous vine development and lush foliage. When flowering begins, switch to phosphorus-rich fertilizers that support flower formation and fruit set. Once fruiting starts, potassium becomes your priority for developing large, sweet watermelons with excellent yields. I adjust my feeding frequency accordingly, providing more frequent applications during early growth stages, then gradually reducing frequency as plants mature to prevent nutrient overload.

Application Method Preferences

How you apply fertilizer to your watermelon plants can dramatically impact nutrient absorption, plant health, and ultimately your harvest success. I recommend considering both foliar sprays and soil applications, as each method offers distinct advantages for different growth phases. Foliar sprays deliver nutrients directly to leaves, providing rapid absorption when your plants need quick energy boosts during flowering or fruit development. Soil applications enhance root uptake, supporting long-term plant health and sustained nutrient availability throughout the growing season. Liquid fertilizers work exceptionally well for both methods, offering fast plant response during essential growth stages. Pay attention to dilution ratios—many concentrates require just a teaspoon per several gallons, making them cost-effective. Choose application methods that match your watering equipment, whether you’re using hose-end sprayers or traditional watering cans.

Soil Ph Compatibility

Why does soil pH matter so much for your watermelon fertilizer choices? I recommend maintaining soil pH between 6.0 and 6.8, as this range maximizes nutrient availability and guarantees your fertilizers work effectively. When pH drops below 5.5, your watermelons can’t absorb nutrients properly, leading to stunted growth and disappointing yields. I always test soil pH before selecting fertilizers, since phosphorus and other essential nutrients become less available in overly acidic or alkaline conditions. If your soil tests too acidic, I suggest adding lime to raise pH levels before applying fertilizers. Remember to monitor pH regularly, as rainfall, irrigation, and fertilizer applications can cause fluctuations over time, affecting how well your chosen fertilizers perform.

Concentration and Dilution

Getting your fertilizer concentration right makes the difference between thriving watermelon plants and damaged crops that struggle to recover. I recommend following manufacturer dilution guidelines carefully, as proper mixing guarantees effective nutrient absorption without causing nutrient burn. Highly concentrated fertilizers often require minimal product per application; for instance, solutions like one teaspoon per two gallons of water provide efficient, cost-effective feeding. The NPK ratio strength directly impacts your dilution strategy, since higher concentrations necessitate more dilution to prevent plant damage. Liquid fertilizers designed for foliar sprays require precise mixing ratios for ideal results, typically more diluted than soil applications. I always emphasize checking concentration recommendations and application frequency, as this maximizes benefits while minimizing over-fertilization risks that can harm your watermelon harvest.

On a final note

I’ve shared my top fertilizer recommendations to help you grow the sweetest, most delicious watermelons possible. Remember that proper nutrition timing, balanced NPK ratios, and consistent feeding schedules make all the difference in fruit development. Whether you choose liquid concentrates or slow-release granules, you’ll see improved yields with these quality products. Start feeding your watermelon plants early, monitor their response, and you’ll harvest incredible, juicy melons this season.