Loading calculator...
Loading calculator...
Optimize plant nutrition with our fertilizer calculator. Get precise NPK recommendations, organic fertilizer options, and application schedules based on your soil test results and crop needs.
Enter values from your soil test. If you don't have a soil test, use default values.
Plants need three primary macronutrients: nitrogen (N) for leafy growth, phosphorus (P) for root development and flowering, and potassium (K) for overall health and disease resistance. Fertilizer labels show N-P-K ratios like 10-10-10 (balanced) or 5-10-5 (bloom booster). Our fertilizer calculator helps you determine the right amount based on your garden size, plant type, and soil test results.
Soil testing reveals existing nutrient levels, preventing over-fertilization which causes pollution and plant damage. Home test kits provide basic pH and N-P-K readings, while university extension lab tests ($15-40) offer comprehensive analysis including micronutrients. Test every 2-3 years, or annually if you're amending heavily. Our calculator interprets results and recommends appropriate fertilizer adjustments.
Organic fertilizers (compost, manure, fish emulsion, bone meal) release nutrients slowly as they decompose, feeding both plants and soil microbes. They're forgiving—hard to over-apply—but take weeks to become available. Synthetic fertilizers provide immediate nutrition but don't improve soil structure and can burn plants if over-applied. Many successful gardeners use both: compost for soil health plus targeted synthetic supplements for heavy feeders.
Different plants have different nutritional needs. Leafy greens (lettuce, spinach, kale) need high nitrogen. Fruiting plants (tomatoes, peppers, squash) need balanced nutrition early, then higher phosphorus when flowering begins. Root vegetables (carrots, beets) need lower nitrogen to avoid excessive top growth. Our calculator adjusts recommendations based on plant type and growth stage for optimal results without waste.
Yes. Over-fertilization burns plant roots, causes excessive leafy growth at expense of fruits, and pollutes waterways through runoff. Symptoms include brown leaf tips, white crust on soil surface, and wilting despite adequate water. Always follow package directions and our calculator recommendations. Less is often more.
Compost provides nutrients but may not be sufficient for heavy feeders like tomatoes and peppers. Soil testing reveals whether supplemental fertilization is needed. Many gardeners use compost as base fertility plus targeted fertilizer for demanding crops. Our calculator accounts for existing compost applications.
Apply fertilizer at planting time (mix into soil or side-dress), then supplement during growing season based on plant needs. Leafy greens benefit from nitrogen every 3-4 weeks. Fruiting plants need phosphorus when flowering begins. Avoid fertilizing during drought or extreme heat. Our calculator provides timing recommendations.