Tomato Fertilizer 4-18-38 | Chelated Micronutrients | Hydroponics, Soil & Foliar Application
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Tomato Fertilizer 4-18-38
Elevate your tomato harvest with our premium water-soluble 4-18-38 formula. This high-potassium fertilizer is specifically designed for tomatoes, peppers, eggplants, potatoes, and other nightshade crops, delivering exceptional fruit development and disease resistance. Enriched with chelated micronutrients and tested for heavy metals, it's the professional choice for soil, hydroponic, and foliar growing.
Ideal Applications
FEATURES
⚖️ Optimized 4-18-38 Ratio
Engineered specifically for fruiting nightshades. Low nitrogen (4%) prevents excessive foliage while very high potassium (38%) drives exceptional fruit size, flavor, and shelf life.
🛡️ Built-In Disease Resistance
High potassium strengthens cell walls against early blight, late blight, and bacterial spot. Chelated copper and manganese further reinforce the plant's natural immune response for healthier crops with fewer chemical interventions.
🚫 Tested for Heavy Metals
Every batch is independently lab tested for heavy metal content so you can grow food for your family or customers with confidence in what you're feeding your plants — and yourself.
🌊 100% Water Soluble
Dissolves instantly in cold water with zero residue. Safe for drip lines, Dutch buckets, NFT systems, and foliar sprayers without clogging risks.
🍅 Maximum Fruit Development
The 38% potassium drives cell expansion for larger tomatoes, enhances sugar transport for better flavor, and strengthens cell walls for longer shelf life.
🌸 Superior Flowering & Fruit Set
18% phosphorus promotes abundant flower formation, strong root systems, and reliable fruit set — reducing blossom drop and improving overall yield.
💧 Soil, Hydroponic & Foliar Versatility
Equally effective in garden soil, raised beds, containers, all hydroponic systems (DWC, NFT, Dutch buckets, drip), and as a foliar spray. Scales from a single potted plant to full commercial acreage through fertigation.
🔬 Complete Micronutrient Package
All six essential micronutrients in precise ratios for nightshade crops — iron, manganese, zinc, and copper are EDTA-chelated to prevent lockout in high-pH water, while boron and molybdenum are supplied in highly available mineral forms.
🥗 Nutrient-Dense Harvest
Higher concentrations of iron (0.10%), zinc (0.05%), and boron (0.02%) don't just feed the plant — they transfer into the fruit itself, producing tomatoes and peppers with greater mineral content for a more nutritious harvest on your table.
📋 CDFA Registered & Lab Verified
Registered with the California Department of Food and Agriculture. Third-party lab tested for guaranteed analysis, purity, and compliance with state fertilizer standards.
DERIVED FROM
Our 4-18-38 formula is blended from premium-grade, solution-grade raw materials — each chosen for purity, solubility, and plant availability.
Macronutrient Sources
Potassium Nitrate
Supplies both potassium and nitrogen in a highly soluble, chloride-free form.
Monopotassium Phosphate
Primary phosphorus and potassium source. Fully water-soluble with low salt index.
Potassium Sulfate
Additional potassium plus sulfur for enzyme activation and protein synthesis.
Ammonium Sulfate
Ammoniacal nitrogen source that helps lower root-zone pH for better nutrient uptake.
Micronutrient Sources
Chelated Iron EDTA
EDTA-protected iron for chlorophyll synthesis. Stays available even in alkaline conditions.
Chelated Manganese EDTA
EDTA-chelated for disease resistance and photosynthesis enzyme activation.
Chelated Zinc EDTA
EDTA-chelated zinc for auxin production, fruit set, and protein synthesis.
Chelated Copper EDTA
EDTA-chelated copper for lignin synthesis and disease resistance.
Boric Acid
Highly available boron source for cell wall formation and pollination.
Sodium Molybdate
Trace molybdenum source for nitrogen metabolism and enzyme function.
SCIENCE BEHIND THE FORMULA
4-18-38: Engineered for Nightshade Crop Performance
Understanding why our 4-18-38 formula works so well for tomatoes and nightshade crops requires looking at the unique nutritional demands of these plants throughout their growth cycle.
🌿 Nitrogen — 4% (Controlled Growth)
Tomatoes need minimal nitrogen during fruiting. Too much causes lush foliage but poor fruit production and delayed ripening. Our 4% provides just enough for healthy photosynthesis without competing with fruit development. This directs the plant's energy where it matters — into your tomatoes.
🌸 Phosphorus — 18% (Flowers & Roots)
During flowering and early fruit development, tomatoes have elevated phosphorus demands for ATP energy transfer, root development and nutrient uptake, flower formation and fruit set, and seed development within the fruit. The 18% level ensures robust reproductive growth.
⭐ Potassium — 38% (Fruit Quality)
Tomatoes are extreme potassium feeders, especially during fruiting. Potassium activates over 60 enzyme systems and directly controls fruit size through cell expansion, flavor through sugar transport, disease resistance through strong cell walls, and shelf life by reducing post-harvest deterioration.
Essential Micronutrients
🧲 Iron (Fe) 0.10%
Chelated EDTA. Essential for chlorophyll synthesis and enzyme function. Prevents interveinal chlorosis (yellowing between leaf veins), especially in alkaline or high-pH conditions.
⚙️ Manganese (Mn) 0.05%
Chelated EDTA. Activates enzymes for photosynthesis and nitrogen metabolism. Critical for disease resistance and pollen germination, directly impacting fruit set rates.
🌱 Zinc (Zn) 0.05%
Chelated EDTA. Required for auxin production and protein synthesis. Improves fruit set and prevents stunted growth and small leaf syndrome.
🔗 Copper (Cu) 0.05%
Chelated EDTA. Involved in lignin synthesis for strong cell walls. Enhances disease resistance and improves fruit quality and firmness.
🧱 Boron (B) 0.02%
Boric Acid. Critical for cell wall formation and sugar transport. Prevents hollow fruits and improves pollination success for better yields.
🔬 Molybdenum (Mo) 0.0005%
Sodium Molybdate. Essential for nitrate reduction and nitrogen metabolism. Though needed in trace amounts, deficiency causes leaf yellowing and stunting.
Why High Potassium?
🍅 Bigger Tomatoes
Potassium regulates water uptake and cell expansion for larger, juicier tomatoes with improved weight and density.
🛡️ Disease Resistance
Strengthens cell walls to resist early blight, late blight, bacterial spot, and other common nightshade diseases.
🍯 Better Flavor
Increases sugar content and improves acid balance for superior taste — the difference between grocery store and garden-fresh.
📦 Longer Shelf Life
Enhances firmness and reduces post-harvest deterioration, keeping your tomatoes fresh longer after picking.
💧 Drought Tolerance
Improves stomatal function and water use efficiency, helping plants cope during hot, dry periods.
🌡️ Stress Resistance
Helps plants recover from temperature extremes, transplant shock, and environmental stress during the growing season.
APPLICATION RATES & DIRECTIONS
Below are recommended rates for tomatoes, peppers, eggplants, potatoes, and other nightshade crops.
Soil Application
| Application Method | Rate | Frequency | Notes |
|---|---|---|---|
| Per Plant | 3g (½ tsp) | Every 4-6 weeks | Apply around base |
| Per 100 sq ft | 0.75-1.25 lbs | Every 4-6 weeks | Broadcast evenly |
| Per Acre | 24-38 lbs | Every 4-6 weeks | Through irrigation |
Foliar Application
| Application Method | Rate | Frequency | Coverage |
|---|---|---|---|
| Per Plant | 1g in water | Every 1-2 weeks | Spray to runoff |
| Per 100 sq ft | 100-150g/gallon | Every 1-2 weeks | Early morning best |
Hydroponic Application (per 100 gallons)
| Growth Stage | 4-18-38 Amount | Cal-Mag Plus | pH Range | EC/PPM |
|---|---|---|---|---|
| Vegetative Growth | 0.5 lbs | 500ml-1L | 6.4-6.6 | 1200 PPM |
| Blooming/Fruiting | 0.5 lbs | 1L | 6.1-6.3 | 1700 PPM |
Optimal Feeding Through Growth Stages
Seedling (Week 0-3): Half strength weekly + Cal-Mag 2.5ml/gal
Vegetative (Week 3-6): Full strength biweekly + Cal-Mag 5ml/gal
Flowering (Week 6-9): Weekly applications + Cal-Mag 7.5ml/gal
Fruiting (Week 9+): Weekly applications + Cal-Mag 10ml/gal
HOW TO USE
Soil & Container Growing
- Dissolve the recommended amount in water (1-2 gallons per application).
- Apply around the base of each plant, avoiding direct contact with stems and foliage.
- Water thoroughly after application to move nutrients into the root zone.
- Apply every 4-6 weeks during the growing season.
- For best results, supplement with Cal-Mag Plus between fertilizer applications.
Hydroponic Systems
- Fill your reservoir with fresh water.
- Add Cal-Mag Plus first and stir thoroughly.
- Add Tomato Fertilizer 4-18-38 and stir until completely dissolved.
- Check and adjust pH to 6.1-6.3 for fruiting stage or 6.4-6.6 for vegetative stage.
- Verify EC/PPM levels match your target growth stage.
- Monitor and top off reservoir as needed, replacing solution every 1-2 weeks.
Foliar Spray
- Dissolve 1g per plant in a spray bottle or backpack sprayer.
- Apply early morning or late afternoon to avoid leaf burn.
- Spray both upper and lower leaf surfaces until runoff.
- Repeat every 1-2 weeks during active growth.
- Do not apply during peak sun hours or when temperatures exceed 90°F.
TOMATO FERTILIZER CALCULATOR
SAFETY & HANDLING
Personal Protective Equipment (PPE)
- Wear gloves and eye protection when handling dry powder or concentrated solutions
- Avoid inhaling dust — use in well-ventilated areas or wear a dust mask when measuring
- Wash hands thoroughly after handling
Storage Guidelines
- Store in a cool, dry place in the original sealed container
- Product is hygroscopic — it will absorb moisture from the air if exposed
- Keep out of direct sunlight and away from heat sources
- If powder clumps from moisture exposure, break it up — efficacy is not affected
- Keep away from children and pets
Application Precautions
- Do not mix dry fertilizer with other products before dissolving in water
- Do not apply foliar sprays during peak sun hours or when temperatures exceed 90°F
- Avoid direct contact with plant stems and foliage when applying to soil
- Water thoroughly after soil application to prevent root burn
First Aid
- Eye contact: Flush with clean water for 15 minutes. Seek medical attention if irritation persists
- Skin contact: Wash affected area with soap and water
- Ingestion: Do not induce vomiting. Contact Poison Control (1-800-222-1222) or seek medical attention
- Inhalation: Move to fresh air. Seek medical attention if symptoms persist
Refer to the Safety Data Sheet (SDS) for complete safety information.
COMPLETE YOUR SYSTEM
Cal-Mag Plus 2-0-0
Prevents blossom end rot and calcium deficiencies. Critical for tomato fruit development in both soil and hydroponic systems.
AlternativeCalcium Nitrate 15.5-0-0
Another calcium source option. Provides a small nitrogen boost during the vegetative stage.
BoostEpsom Salt (Magnesium Sulfate)
Magnesium for chlorophyll production. Enhances green color, photosynthesis, and overall plant vigor.
FREQUENTLY ASKED QUESTIONS
Why is the potassium (38%) so high in this formula?
Tomatoes are extreme potassium feeders, especially during fruiting. Potassium activates over 60 enzyme systems and directly controls fruit size and weight, sugar content and flavor, disease resistance against blight and bacterial spot, and post-harvest shelf life. The 38% ensures your plants never run short during the critical fruiting period when potassium demand peaks.
What pH should I maintain for tomatoes?
Tomatoes prefer slightly acidic conditions. For hydroponics, keep pH between 6.1-6.3 during fruiting or 6.4-6.6 during vegetative growth. For soil growing, aim for 6.2-6.5. pH directly affects nutrient availability — outside these ranges, key nutrients like iron and phosphorus become locked out even when present in the solution.
How do I prevent blossom end rot?
Blossom end rot is caused by calcium deficiency in developing fruit. Our formula does not contain calcium because calcium and phosphorus are chemically incompatible in the same solution — when mixed, they form insoluble calcium phosphate that precipitates out and becomes unavailable to plants. That's why any high-phosphorus fertilizer must be supplemented with a separate calcium source.
Our formula still helps reduce BER risk because low nitrogen prevents excessive foliage that competes for calcium, and high potassium improves water regulation for better calcium transport to developing fruit.
Recommended calcium sources:
- Cal-Mag Plus 2-0-0 — best for hydroponic systems and container growing
- Calcium Nitrate 15.5-0-0 — water-soluble option with a small nitrogen boost
- Gypsum (Calcium Sulfate) — excellent organic-approved calcium source that won't alter soil pH
- Bone Meal 3-15-0 — slow-release organic calcium and phosphorus for soil gardens
Consistent watering is also critical — irregular watering prevents calcium uptake even when it's available in the soil.
Can I use this for all tomato and pepper varieties?
Yes. This formula is ideal for all nightshade family plants including tomatoes (beefsteak, cherry, roma, heirloom), all pepper types (bell, hot, sweet), eggplants (standard and Asian varieties), potatoes, and specialty crops like tomatillos and goji berries. Larger plants like beefsteak tomatoes may need 25% more fertilizer than cherry tomatoes due to their greater biomass.
Why does potassium matter so much for fruit quality?
Potassium is the nutrient most directly responsible for fruit quality in nightshade crops. It regulates water movement into cells (bigger fruit), drives sugar transport from leaves to fruit (better flavor), and strengthens cell walls (disease resistance and firmness). Our article on The Role of Potassium in Fruit Development covers this in depth with research-backed guidance.
How do I store the powder?
Our fertilizer is highly hygroscopic, meaning it absorbs moisture from the air. Keep the bag sealed tight between uses and store in a cool, dry place out of direct sunlight. If it clumps from moisture exposure, simply break it up — the efficacy is not affected.
What role does nitrogen play at just 4%?
The low 4% nitrogen is intentional. During fruiting, excessive nitrogen causes lush foliage at the expense of fruit production and delays ripening. Our 4% provides just enough to maintain healthy green leaves for photosynthesis without diverting energy from fruit development. For more on nitrogen's role, read our article What's the Function of Nitrogen in Plants?
GROW WITH CONFIDENCE
Important details on quality, returns, sustainability, and charitable efforts that set our product apart.
Product Quality Guaranteed
- Manufactured in Madera, California, USA
- Tested by independent third-party laboratories for purity and guaranteed analysis
- Registered with the California Department of Food and Agriculture (CDFA)
- Rigorously tested to ensure products are free from heavy metals
- 100% chelated micronutrients for maximum bioavailability
Hassle-Free Return Policy
If you're not completely satisfied, we offer a 90-day money-back guarantee. Simply return the unused portion in its original packaging, and we'll process a full refund. No questions asked.
Environmental Responsibility
We're committed to sustainable practices, including:
- Recyclable packaging materials
- Precise nutrient formulation to reduce environmental runoff
- Support for integrated pest management (IPM) practices
- Promoting efficient nutrient delivery systems like hydroponics
Charitable Contributions
1% of all profits go to our foundation, focused on improving educational opportunities for children in agricultural communities.
DOCUMENTS
- 📄 Safety Data Sheet (SDS)
- 📋 Product Label / CDFA Registration
- 🔬 Certificate of Analysis (COA) — Available upon request
DISCOVER MORE
- What's the Function of Nitrogen in Plants? — Understand why 4% nitrogen is the sweet spot for fruiting crops
- What's the Function of Phosphorus in Plants? — Learn how phosphorus drives flowering and root development
- The Role of Potassium in Fruit Development — Why 38% potassium transforms tomato quality and yield
HAVE QUESTIONS?
Check out our full FAQ page or contact our experts for personalized advice.