10 Best Watermelon Fertilizers for Sweeter, Juicier Fruit

I’ve found that specialized watermelon fertilizers like LEAVES AND SOUL’s 5-1-5 concentrate and Farmer’s Secret Fruit & Bloom Booster greatly increase sugar content through targeted nutrition. These liquid formulations, along with FoxFarm Big Bloom and Premium Liquid Silica supplements, deliver essential nutrients directly to developing fruits during critical growth phases. The key lies in timing applications correctly—nitrogen-rich fertilizers during vine development, then switching to potassium-heavy formulas during fruit maturation to maximize sweetness and enhance overall fruit quality through proper nutritional balance.

We are supported by our audience. When you purchase through links on our site, we may earn an affiliate commission, at no extra cost for you. Learn more. Last update on 11th September 2025 / Images from Amazon Product Advertising API.

Notable Insights

• LEAVES AND SOUL Professional Liquid Melon Fertilizer offers a specialized 5-1-5 ratio perfect for balanced watermelon growth and fruit development.
• Farmer’s Secret Fruit & Bloom Booster enhances late-season fruit production with super concentrated formula designed to maximize sweetness levels.
• FoxFarm Big Bloom provides organic nutrition from natural ingredients, promoting enhanced flavor in flowering and fruiting watermelon plants.
• Apply nitrogen-rich fertilizers during early growth, then transition to phosphorus for flowering and potassium during fruit maturation phases.
• Premium Liquid Silica strengthens plant cell walls and stems, improving overall fruit quality while protecting against environmental stress.

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

For gardeners seeking a specialized solution that bridges the gap between beginner-friendly application and professional-grade results, LEAVES AND SOUL Professional Liquid Melon Fertilizer delivers targeted nutrition specifically formulated for watermelon cultivation. This 5-1-5 concentrate provides balanced nitrogen for vigorous vine growth, minimal phosphorus for root development, and potassium for fruit quality enhancement. You’ll appreciate the liquid format’s convenience, as it mixes effortlessly with water and eliminates measuring complications common with granular alternatives. The premium ingredient blend supports both seedlings and mature plants, ensuring consistent nutrition throughout your growing season. Users consistently report improved plant health and increased yields, making this fertilizer effective for both novice and experienced watermelon growers.

Best For: Gardeners of all experience levels who want a specialized, easy-to-use liquid fertilizer specifically formulated for watermelon cultivation with professional-grade results.

Pros:

• Specialized 5-1-5 nutrient ratio specifically designed for optimal watermelon growth, promoting vigorous vines and quality fruit development
• Easy-to-use liquid concentrate format that mixes effortlessly with water, eliminating measuring complications of granular fertilizers
• Versatile formula that effectively supports both seedlings and mature plants throughout the entire growing season

Cons:

• Limited to 8 oz size which may require frequent repurchasing for larger gardens or multiple growing seasons
• Specialized formulation makes it less versatile for other types of plants beyond melons
• Higher cost per application compared to general-purpose granular fertilizers

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

Watermelon growers seeking maximum fruit production during the critical late-season development phase will find exceptional value in Farmer’s Secret Fruit & Bloom Booster Fertilizer, a powerhouse solution that transforms struggling plants into abundant producers. This super concentrated formula strengthens root systems, enhancing nutrient uptake that directly translates to sweeter, juicier watermelons. You’ll appreciate the economical dilution rate of just one teaspoon per two gallons of water, making this 16-ounce bottle stretch remarkably far throughout your growing season. Apply every 2-4 weeks during late summer and early fall when your watermelon plants need essential nutrients most, simply mixing the concentrate into your regular watering routine for effortless garden maintenance.

Best For: Watermelon growers and gardeners who want to maximize fruit production and sweetness during the critical late-season development phase of their plants.

Pros:

• Super concentrated formula with economical dilution rate (1 teaspoon per 2 gallons) makes the 16oz bottle last throughout the growing season
• Strengthens root systems to enhance nutrient uptake, resulting in sweeter and juicier watermelons
• Easy application that integrates seamlessly into regular watering routine with flexible 2-4 week intervals

Cons:

• Specifically formulated for late summer and early fall application, limiting use to seasonal timing
• Requires proper dilution which may be inconvenient for some users who prefer ready-to-use products
• No specific nutrient analysis or ingredient breakdown provided for growers who want detailed fertilizer composition

Premium Liquid Silica Plant Supplement – 8oz Watermelon Plants Fertilizer

Although silica supplementation might seem like an advanced technique, this Premium Liquid Silica Plant Supplement transforms complex plant nutrition into an accessible solution that benefits gardeners at every skill level. You’ll strengthen your watermelon stalks and prevent breakage by reinforcing plant cell walls with organic acid chelated silica from sand and plant extracts. This bio-available formula remains accessible in soil for faster uptake, helping your plants resist environmental stress from heat, drought, and humidity while promoting thicker leaves and sturdier stems. The 8-ounce bottle makes 45 gallons of nutrient-rich solution, offering versatile application methods including watering cans, hose sprayers, and foliar feeding for both hydroponic and soil gardens.

Best For: Gardeners of all skill levels who want to strengthen their watermelon plants’ structural integrity and improve resistance to environmental stress while ensuring cost-effective nutrition supplementation.

Pros:

• Bio-available silica formula strengthens plant cell walls, preventing stalk breakage and promoting thicker leaves and sturdier stems
• Versatile application methods including watering can, hose sprayer, and foliar feeding work for both hydroponic and soil gardens
• Highly concentrated solution with excellent value – 8oz bottle makes 45 gallons of nutrient-rich fertilizer

Cons:

• Product is specifically marketed for watermelon plants, which may limit perceived versatility for other crops
• Requires different mixing ratios for various application methods, which could be confusing for beginners
• Advanced bio-available silica formulation may be unnecessary for casual gardeners with basic fertilizer needs

FoxFarm Big Bloom Plant Food Liquid Fertilizer Concentrate (Pint)

Organic gardening enthusiasts who prioritize natural soil enhancement will find FoxFarm Big Bloom Plant Food an exceptional choice for nurturing robust watermelon plants. This micro-brewed liquid concentrate features earthworm castings and bat guano, delivering essential nutrients through a gentle 0-0.5-0.7 NPK formula. You’ll appreciate how this organic blend enhances root development while intensifying the natural sweetness and flavor of your watermelons without introducing harmful chemicals. The concentrate mixes easily with water in your watering can, making regular feeding sessions simple and effective for both garden beds and container-grown plants.

Best For: Organic gardening enthusiasts who want to enhance the flavor and fragrance of flowering and fruiting plants, herbs, and vegetables using natural ingredients without harmful chemicals.

Pros:

• Contains natural, organic ingredients like earthworm castings and bat guano that enhance root development and boost plant flavor
• Safe for regular use on all types of flowering and fruiting plants, both indoors and outdoors
• Easy to mix and apply with water, making feeding sessions simple and convenient

Cons:

• Low NPK ratio (0-0.5-0.7) may not provide sufficient nutrition for heavy-feeding plants during peak growing seasons
• Higher cost per application compared to synthetic fertilizers with concentrated nutrient levels
• May require more frequent applications to achieve desired results due to gentle, slow-release formula

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

Gardenera’s fast-acting liquid concentrate delivers professional-grade nutrition specifically formulated for watermelon cultivators seeking maximum fruit size, sweetness, and overall yield performance. You’ll appreciate the balanced NPK formulation that supports vigorous vine growth, robust flowering, and exceptional fruit development in popular varieties like Sugar Baby and Crimson Sweet. The formula’s low pH of 1.69 reveals essential micronutrients including iron, manganese, and zinc, particularly benefiting plants in alkaline soil conditions. You can expect noticeable improvements in fruit quality within weeks, as the organic acids enhance soil structure and nutrient absorption throughout your watermelon’s growth cycle from transplant to harvest.

Best For: Watermelon growers who want professional-grade nutrition to maximize fruit size, sweetness, and yield in both indoor and outdoor cultivation settings.

Pros:

• Fast-acting liquid concentrate with balanced NPK formulation specifically designed for watermelon varieties like Sugar Baby and Crimson Sweet
• Low pH of 1.69 unlocks essential micronutrients and improves nutrient absorption, especially beneficial for alkaline soils
• Versatile application for containers, greenhouses, and open gardens with noticeable improvements in fruit quality within weeks

Cons:

• Small 8 oz size may require frequent repurchasing for larger watermelon operations or multiple plants
• Extremely low pH of 1.69 requires careful handling and proper dilution to avoid potential plant or soil damage
• Specialized formulation limits use to watermelons and similar crops, reducing versatility compared to general-purpose fertilizers

Miracle-Gro Performance Organics Edibles Plant Nutrition (1 lb.)

Miracle-Gro Performance Organics Edibles Plant Nutrition delivers instant feeding power that makes it perfect for gardeners who want certified organic nutrition without sacrificing convenience. This OMRI-listed organic fertilizer specifically targets edible crops like watermelons, tomatoes, vegetables, herbs, and fruits with a formulation designed to promote bountiful harvests. You can apply it easily using the Miracle-Gro Performance Organics Garden Feeder or a standard watering can, feeding your watermelon plants every seven days throughout the growing season. The one-pound container covers up to 265 square feet when used with the garden feeder, providing excellent value for larger watermelon patches or multiple container plantings.

Best For: Gardeners who want certified organic nutrition for their edible crops including tomatoes, vegetables, herbs, and fruits without sacrificing the convenience of instant feeding.

Pros:

• OMRI-listed organic fertilizer that feeds plants instantly while maintaining organic certification
• Easy application with multiple methods using either the Performance Organics Garden Feeder or standard watering can
• Excellent coverage of up to 265 square feet per one-pound container when used with the garden feeder

Cons:

• Requires frequent application every 7 days throughout the growing season which may be time-consuming
• Limited to edible crops only, so not suitable for ornamental plants or flowers
• May be more expensive than conventional fertilizers due to organic certification and specialized formulation

TPS Plant Foods Watermelon Liquid Fertilizer, 8 oz

TPS Plant Foods Watermelon Liquid Fertilizer delivers exceptional results for gardeners who want to maximize their watermelon harvest, whether you’re growing compact Sugar Babies or sprawling striped giants. This 8-ounce liquid formula combines balanced NPK ratios with essential micronutrients, promoting vigorous vine growth, abundant flowering, and ideal fruit development throughout the growing season. You’ll appreciate how easily this fertilizer mixes with water, ensuring fast absorption and quick results that support strong root systems and healthy spreading vines. The specialized formula works effectively from initial flowering stages through fruit maturation, helping you achieve lush, productive vines loaded with crisp, sweet watermelons that make your gardening efforts truly rewarding.

Best For: Gardeners who want to grow large, sweet watermelons of any variety and need a specialized liquid fertilizer that supports vigorous vine growth and fruit development from flowering through harvest.

Pros:

• Balanced NPK formula with essential micronutrients specifically designed for watermelon cultivation
• Easy-to-mix liquid format provides fast absorption and quick results throughout all growth stages
• Works effectively for all watermelon varieties from compact Sugar Babies to large striped giants

Cons:

• Small 8-ounce size may require frequent repurchasing for larger gardens or multiple plants
• Specialized formula is only designed for watermelons, limiting versatility for other crops
• No specific NPK ratios or micronutrient details provided for informed comparison with other fertilizers

10-10-10 All Purpose Plant Food – Liquid Fertilizer (1x8oz)

Budget-conscious gardeners seeking a reliable, all-purpose solution will find exceptional value in this 10-10-10 liquid fertilizer, which delivers balanced nutrition that watermelons need throughout their growing season. The equal ratios of nitrogen, phosphorus, and potassium provide thorough plant support, promoting healthy foliage development, strong root systems, and robust fruit production. You’ll appreciate the enhanced formula’s seaweed extract and chelated iron, which supply essential micronutrients and prevent yellowing leaves across various soil conditions. The simple mix-and-apply application makes feeding your watermelon plants effortless, whether you’re managing container gardens or expansive outdoor plots with irrigation systems.

Best For: Budget-conscious gardeners who want a versatile, easy-to-use liquid fertilizer that works effectively for both indoor and outdoor plants, from houseplants to vegetable gardens.

Pros:

• Balanced 10-10-10 formula with added seaweed extract and chelated iron provides comprehensive nutrition and prevents chlorosis across various soil pH levels
• Simple mix-and-apply application makes it beginner-friendly while being effective enough for experienced gardeners with advanced irrigation systems
• Versatile formula works for multiple plant types including vegetables, flowers, houseplants, and shrubs, eliminating the need for multiple specialized fertilizers

Cons:

• Small 8oz package size may not be sufficient for large garden operations or frequent feeding schedules
• Some customers have reported initial packaging issues, though these appear to be resolved quickly by the seller
• Limited information provided about specific dilution ratios or feeding frequency recommendations for different plant types

Triple 10 All Purpose Liquid Fertilizer 10-10-10 (32oz)

For gardeners seeking a versatile, all-in-one solution that supports watermelons throughout their entire growing cycle, the Triple 10 All Purpose Liquid Fertilizer delivers balanced nutrition with remarkable convenience. This high-concentrate formula features a 10-10-10 NPK ratio, providing equal amounts of nitrogen, phosphorus, and potassium that watermelons need for vigorous growth and fruit development. You’ll appreciate the added amino acids and seaweed extract, which enhance nutrient uptake and plant resilience during stressful growing conditions. The easy-measure bottle design allows precise dosing at 1-2 ounces per gallon, creating up to 32 gallons of fertilizer solution from one container. Apply every 1-2 weeks throughout the season for consistent results.

Best For: Gardeners who want a versatile, all-purpose fertilizer that works for watermelons and other plants throughout all growth stages, both indoors and outdoors.

Pros:

• Balanced 10-10-10 NPK ratio with added amino acids and seaweed extract for enhanced plant health and nutrient uptake
• High-concentrate formula creates up to 32 gallons of fertilizer solution from one 32oz bottle, providing excellent value
• Easy-measure bottle design allows precise dosing with simple squeeze action for consistent application

Cons:

• May require frequent applications every 1-2 weeks throughout the growing season, increasing maintenance time
• Equal NPK ratio might not be optimal for plants that need specific nutrient ratios during different growth phases
• Liquid formula requires mixing with water before each application rather than being ready-to-use

Burpee Organic Blood Meal Fertilizer for Tomatoes & Leafy Greens (3 lb)

Nitrogen-hungry watermelon plants thrive with Burpee Organic Blood Meal Fertilizer, a high-nitrogen solution that delivers exceptional results for gardeners seeking robust vine development and abundant fruit production. This OMRI-listed organic fertilizer provides a 12-0-0 NPK ratio, supplying readily available nitrogen that encourages vigorous leaf growth and strong vine establishment during watermelon’s critical early stages. You’ll appreciate how this traditional fertilizer supports beneficial soil microorganisms while promoting the lush, green foliage essential for photosynthesis and fruit development. The added pest-deterrent properties help protect your watermelon patch from deer, rabbits, and moles, creating a natural barrier around your plants while nourishing them with time-tested effectiveness.

Best For: Organic gardeners growing nitrogen-hungry vegetables like tomatoes, leafy greens, and watermelons who want a natural fertilizer that also deters common garden pests.

Pros:

• High nitrogen content (12-0-0) provides readily available nutrients for vigorous plant growth and lush foliage
• OMRI-listed organic certification ensures suitability for organic gardening practices
• Natural pest deterrent properties help repel deer, rabbits, and moles from garden areas

Cons:

• Limited to nitrogen-only nutrition, requiring additional fertilizers for phosphorus and potassium needs
• Strong odor from blood meal may be unpleasant for some gardeners during application
• Not suitable for all plants, as some may be sensitive to high nitrogen levels or could experience nutrient burn

Factors to Consider When Choosing Watermelon Fertilizer

When I’m helping you select the perfect fertilizer for your watermelons, several key factors will determine your success in the garden. The NPK ratio becomes essential since watermelons need specific nutrient balances at different growth stages, while your choice between liquid and granular forms affects application frequency and nutrient release rates. I’ll also guide you through deciding between organic and synthetic options, timing applications correctly, and ensuring your fertilizer works well with your soil’s pH level.

NPK Ratio Requirements

Understanding the proper NPK ratio forms the foundation of successful watermelon cultivation, as these three essential nutrients work together to support every stage of plant development. I recommend targeting a 5-1-5 NPK ratio, which provides the balanced nutrition watermelons need throughout their growing cycle. During early growth phases, nitrogen promotes vigorous vine development and lush foliage, creating the strong plant structure necessary for heavy fruit production. As your plants evolve to flowering, phosphorus becomes essential for robust root systems and successful bloom formation. Potassium takes center stage during fruit maturation, directly influencing both watermelon size and sweetness levels. Additionally, selecting fertilizers with lower pH formulations helps reveal essential micronutrients, enhancing overall plant health and maximizing your harvest potential.

Liquid Vs Granular

Choosing between liquid and granular fertilizers requires careful consideration of your watermelon plants’ specific needs, your soil conditions, and your preferred gardening schedule. Liquid fertilizers offer faster absorption rates, making nutrients readily available for quick growth phases like flowering and fruiting. They’re easier to mix with water and provide more accurate measurements, though they’ll require reapplication every 2-4 weeks. Granular fertilizers release nutrients slowly, providing steady nourishment throughout your watermelon’s life cycle, and they last several weeks or months before needing replacement. I recommend liquid fertilizers for sandy soils that drain quickly, while granular options work better in moisture-retaining soils that hold nutrients longer.

Organic Vs Synthetic

How do you decide between organic and synthetic fertilizers for your watermelon plants? I recommend considering your long-term soil health goals alongside your immediate growing needs. Organic fertilizers, derived from natural sources like blood meal, release nutrients slowly while improving soil structure and promoting beneficial microbial activity that supports sustained plant health. They’ll also help repel certain pests naturally. Synthetic fertilizers provide immediate nutrient availability for rapid growth, offering precise formulations designed specifically for watermelon requirements. However, they can cause nutrient leaching and don’t contribute to long-term soil improvement. If you’re committed to sustainable gardening practices, organic options reduce environmental impact by preventing chemical runoff, while synthetic fertilizers require careful application to avoid soil and water pollution.

Growth Stage Timing

When you time your fertilizer applications to match your watermelon’s growth stages, you’ll maximize both plant health and fruit production throughout the growing season. During early vegetative growth, I focus on nitrogen-rich fertilizers to promote robust foliage development and strong vine establishment. As plants shift into flowering, I switch to phosphorus-heavy applications that support flower production and enhance root system health. Once fruits begin developing, potassium becomes my priority nutrient, directly improving fruit size, sweetness levels, and overall yield quality. I maintain regular feeding schedules every 2-4 weeks, adjusting nutrient ratios based on each growth phase. Early applications encourage vigorous plant development, while later applications guarantee proper fruit maturation and sugar concentration for that perfect harvest.

Soil Ph Compatibility

Although many gardeners overlook this essential factor, soil pH compatibility directly determines how effectively your watermelon plants can absorb the nutrients you’re providing through fertilization. I recommend testing your soil before selecting fertilizers, as watermelons thrive in slightly acidic to neutral conditions with pH levels between 6.0 and 7.0. When your soil falls outside this range, even premium fertilizers won’t deliver ideal results because nutrient availability becomes compromised. If you’re dealing with alkaline soil, choose fertilizers with lower pH levels to help release essential micronutrients that your plants desperately need. I suggest monitoring pH throughout the growing season, making adjustments as necessary to maintain that sweet spot where your watermelons can access maximum nutrition for superior growth and fruit development.

Concentration and Dilution

Since watermelon fertilizers frequently arrive in concentrated forms, understanding proper dilution ratios becomes crucial for achieving ideal plant nutrition without causing stress or damage. I’ve found that most concentrated fertilizers require specific measurements, typically ranging from teaspoons per gallon of water, which guarantees your watermelons receive maximum nutrient absorption. These high-concentration formulations offer remarkable efficiency, allowing you to achieve effective results with minimal quantities while maximizing cost savings. For example, an 8-ounce bottle can produce up to 45 gallons of nutrient solution, demonstrating the impressive potential of concentrated fertilizers. Following recommended dilution guidelines prevents plant stress and ensures sufficient nutrient delivery, while lower pH concentrated fertilizers enhance micronutrient availability for healthier growth and superior fruit development.

Application Method Options

While selecting the right fertilizer formula remains important, choosing an effective application method can greatly impact your watermelon crop’s nutrient absorption and overall success. I recommend considering three primary application approaches that offer distinct advantages for different gardening situations. Watering can applications provide precise control over fertilizer placement, allowing you to target individual plants while maintaining consistent dilution ratios. Foliar sprays deliver nutrients directly through leaf surfaces, promoting faster uptake during critical growth periods. Hose-end sprayers offer efficient coverage for larger watermelon patches, distributing liquid concentrates evenly across multiple plants. Each method accommodates specific dilution requirements, typically one teaspoon per gallon, ensuring proper nutrient delivery without over-fertilization risks that could damage your developing watermelons.

On a final note

I’ve shared my top fertilizer recommendations to help you grow the sweetest, most delicious watermelons possible. Remember that consistent feeding throughout the growing season, combined with proper watering and soil preparation, creates the foundation for exceptional fruit quality. Start with these proven products, monitor your plants’ response, and adjust your feeding schedule accordingly. With the right fertilizer choice and careful attention, you’ll harvest watermelons that’ll make your summer gardening efforts truly worthwhile.