Guaranteed Analysis
Nutrient Breakdown
N · Nitrogen10%
Provides 10% nitrogen (from ammonium sulfate and polymer-coated urea) for steady growth without the excessive vegetative push that reduces fruit quality in fruiting crops
P · Phosphorus5%
Delivers 5% phosphorus (from monoammonium phosphate) for root establishment and flower initiation—kept intentionally low to avoid phosphorus buildup in established soils
K · Potassium13%
Supplies 13% potassium (from muriate of potash and potassium magnesium sulfate) to improve fruit quality, firmness, flavor, color development, and disease resistance
Derived from: Ammonium Sulfate, Purkote (Polymer Coated Urea), Monoammonium Phosphate, Potassium Chloride (Muriate of Potash), Potassium Magnesium Sulfate, Calcium Sulfate (Gypsum). Also provides 13% Sulfur, 3% Calcium, 3% Magnesium.
Overview
What It Is
This 10-5-13 tomato formula uses the same blend as the Strawberry Fertilizer and 10-5-13 general-purpose fertilizer—all three share the same Green Mountain Fertilizer formulation. The moderate 10% nitrogen prevents the common mistake of over-fertilizing tomatoes with high-nitrogen products, which causes lush green plants that flower late and produce fewer fruit. The extended-release nitrogen from Purkote ensures steady supply over weeks.
The high potassium-to-nitrogen ratio (13:10) is intentional—tomatoes in the fruiting stage need significantly more potassium than nitrogen. Potassium drives sugar transport to developing fruit and is directly linked to flavor, color, and shelf life. The 3% calcium from gypsum is delivered in sulfate form that does not alter soil pH, providing consistent calcium to prevent blossom-end rot.
Crop Fit
Best For
TomatoesPeppersEggplantTomatillosGround CherriesCucumbersSquashMelons
Optimized for tomatoes but benefits all nightshade (Solanaceae) crops including peppers, eggplant, and tomatillos. Cucumbers, squash, and melons also respond well to the high-potassium profile during fruiting. The calcium and magnesium content benefits all heavy-fruiting crops prone to blossom-end rot.
Application Rates
How Much to Use
| Garden & beds | 0.75-1.5 lbs per 100 sq ft broadcast before planting; 1-2 tablespoons per plant as side-dress every 3-4 weeks during fruiting |
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| Lawn | N/A — crop-specific fertilizer formulated for tomatoes, not turf |
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| Trees & shrubs | N/A — not formulated for tree application |
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| Containers | 1 tablespoon per gallon of soil at planting; side-dress with 1 teaspoon per plant every 3-4 weeks |
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| Frequency | Apply at planting, then side-dress every 3-4 weeks once fruit begins to set. 2-3 applications per season for most crops. |
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Step by Step
How to Apply
1Soil Test
Test soil before the season to determine baseline nutrient levels and adjust application rates accordingly.
2At Planting
At planting, work 0.75–1.5 lbs per 100 sq ft into the bed, or mix 1 tbsp per gallon of soil for containers.
3Establishment Period
Allow transplants 2–3 weeks to establish before first side-dress. Early feeding can shock young plants.
4Side-Dress Schedule
Side-dress 1–2 tablespoons per plant every 3–4 weeks once fruit sets to sustain heavy production.
5Application Method
Apply in a ring 6 inches from the stem to target feeder roots without contacting the main stem.
6Water In
Water thoroughly after each application to dissolve granules and prevent root zone salt buildup.
7Late Season
Reduce applications as harvest winds down. Late-season feeding wastes fertilizer and delays plant senescence.
At transplanting, incorporate fertilizer at 0.75-1.5 lbs per 100 sq ft. Once fruit begins to set, side-dress every 3-4 weeks with 1-2 tablespoons per plant in a shallow ring 6 inches from the stem. For indeterminate varieties, maintain this schedule until 3-4 weeks before last harvest. For containers, use 1 teaspoon per plant per application. For commercial production, apply 200-400 lbs per acre split across pre-plant and 2-3 side-dress applications.
Handling & Timing
Safety & Season
Safety & Storage
Wear protective gloves and eye protection during handling. Avoid breathing dust—use a NIOSH-approved respirator in dusty conditions. Wash hands thoroughly after handling. Store in a cool, dry, well-ventilated area protected from weather and moisture. Slightly reactive with oxidizing agents, metals, alkalis. Prevent entry to sewers and surface waters. Keep out of reach of children and pets.
Seasonal Notes
Spring: Apply at transplanting after soil reaches 60°F. Summer: Primary side-dressing season every 3-4 weeks as fruit sets. This is when potassium demand peaks. Fall: Final applications for late-season production. Stop 3-4 weeks before first frost. Winter: No application. Plan soil testing.
In Context
How It Compares
This 10-5-13 provides the high potassium-to-nitrogen ratio tomatoes need during fruiting, unlike balanced 10-10-10. The 3% calcium specifically targets blossom-end rot prevention. The extended-release nitrogen reduces application frequency. This is the same formulation as Old Cobblers Farm™ Strawberry Fertilizer and 10-5-13 Fertilizer.
Answers
Frequently Asked Questions
What is the best tomato fertilizer?
The best tomato fertilizer provides moderate nitrogen for vine growth, moderate phosphorus for root health and flowering, and elevated potassium for fruit quality. A 10-5-13 ratio with micronutrients is ideal because potassium directly improves tomato size, flavor, color, firmness, and disease resistance. Added calcium helps prevent blossom end rot, while boron and zinc support pollination and fruit set. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 with micronutrients is specifically engineered for bigger, tastier, healthier tomatoes from every plant in your garden.
When should I fertilize tomato plants?
Fertilize tomatoes at transplanting by mixing fertilizer into the planting hole, then side-dress when the first flowers appear, and reapply every 4–6 weeks throughout the fruiting season. Avoid heavy nitrogen applications before flowering, as this promotes excessive foliage at the expense of fruit. Container tomatoes may need feeding every 2–3 weeks due to nutrient leaching. Stop fertilizing about 4 weeks before your last expected harvest. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 provides steady, season-long nutrition for continuous tomato production.
How much fertilizer per tomato plant?
Apply 1–2 tablespoons of 10-5-13 tomato fertilizer per plant at transplanting, mixed into the soil around the root ball. For side-dressing, apply 1 tablespoon per plant in a ring 4–6 inches from the stem every 4–6 weeks. For raised beds, broadcast 2 pounds per 100 square feet before planting. For container tomatoes (5-gallon pots), use 1 tablespoon every 2–3 weeks. Always water deeply after application. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 is easy to measure for precise, consistent feeding throughout the season.
What does potassium do for tomatoes?
Potassium is the single most important nutrient for tomato fruit quality. It controls water regulation within the plant, improving drought tolerance during the critical fruiting period. Potassium directly enhances tomato size, red color development, sugar content (flavor), firmness, and shelf life. It also activates enzymes involved in disease resistance, reducing susceptibility to early blight, fusarium wilt, and other common tomato diseases. Plants with adequate potassium produce larger, tastier, more disease-resistant tomatoes. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 delivers 13% potassium specifically for superior tomato quality.
How do I prevent blossom end rot on tomatoes?
Blossom end rot is caused by calcium deficiency within the developing fruit, often triggered by inconsistent watering rather than a lack of calcium in the soil. To prevent it: maintain even, consistent moisture through regular watering and mulching; avoid excessive nitrogen which inhibits calcium uptake; and use a tomato fertilizer that includes calcium and micronutrients. Avoid overwatering and underwatering cycles. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 includes calcium and balanced micronutrients to help prevent blossom end rot when combined with consistent watering practices.
Is 10-5-13 better than 10-10-10 for tomatoes?
For established tomato plants in the fruiting stage, 10-5-13 is generally better than 10-10-10. The higher potassium in 10-5-13 directly improves fruit quality, while the lower phosphorus avoids oversupplying a nutrient that most garden soils already have in adequate amounts. However, 10-10-10 works well for new gardens or soils that need comprehensive nutrition. For the best results, use a balanced fertilizer at planting and switch to 10-5-13 once plants begin flowering. Old Cobblers Farm™ offers both the Tomato Fertilizer 10-5-13 and the Garden & Tomato 10-10-10 to match different growing situations.
What micronutrients do tomatoes need?
Tomatoes benefit from several key micronutrients. Calcium prevents blossom end rot and strengthens cell walls. Boron improves pollination and fruit set. Iron and manganese support chlorophyll production and photosynthesis. Zinc aids growth regulation and disease resistance. Magnesium is essential for chlorophyll production and energy transfer. These micronutrients work synergistically with NPK to produce healthier plants, more flowers, and higher-quality fruit. Old Cobblers Farm™ Wicked Growth Tomato Fertilizer 10-5-13 includes a complete micronutrient package for optimized tomato health and production.
