An indoor plant fertilizer calculator gives you the correct NPK dilution ratio and application frequency for your specific houseplant — plus a month-by-month calendar showing when to fertilize and when to stop for dormancy.
Fertilizer Settings
Your Fertilizer Plan
Monthly Fertilizing Calendar
Select a plant and enter NPK values,
then click Calculate.
How to Use the Indoor Plant Fertilizer Calculator
Fertilizing houseplants is one of the most commonly mishandled aspects of plant care. Most people either never fertilize (leading to nutrient deficiency) or fertilize year-round without adjusting for dormancy (causing fertilizer burn from salt buildup). This calculator gives you a plant-specific dilution and a month-by-month seasonal calendar.
Reading Your Fertilizer Label
Every fertilizer label shows three numbers separated by dashes — that's the NPK ratio. A 10-10-10 fertilizer contains 10% nitrogen, 10% phosphorus, and 10% potassium. A 3-1-2 fertilizer has 3% nitrogen, 1% phosphorus, 2% potassium. Enter these numbers into the calculator. Higher numbers are more concentrated; they should be diluted more to avoid burning plant roots.
Plant-Specific Recommendations
The calculator matches your plant to a preferred NPK type: foliage plants (pothos, monsteras, philodendrons) prefer high-N ratios that drive leafy growth. Flowering plants need higher phosphorus to support blooms. Cacti and succulents do best with balanced, low-concentration fertilizer at half strength. The recommendation explains whether your current fertilizer ratio is ideal, acceptable, or worth swapping out.
Understanding the Seasonal Calendar
The monthly calendar shows when to fertilize at full strength (peak growing season, April-August), half strength (transitional months), and when to stop completely (winter dormancy, November-February for most plants). This pattern aligns with natural light cycles — plants need nutrients when they're actively growing, not during the short-day winter months when they're conserving energy.
Application Tips
Always water your plant with plain water before applying fertilizer — never apply to dry soil. The diluted fertilizer solution should be applied during or immediately after a regular watering session. For liquid fertilizers, mix the recommended amount per liter and apply until it drains from the drainage holes. Flush with plain water every 2-3 months to remove accumulated mineral salts.
FAQ
Is this tool free?
Yes, completely free with no signup required.
Is my data safe?
Yes, all calculations run locally in your browser. Nothing is sent to any server.
What does NPK mean on fertilizer labels?
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) — the three primary macronutrients plants need. The numbers on a fertilizer label (e.g., 10-10-10 or 3-1-2) represent the percentage of each nutrient by weight. Nitrogen drives leafy green growth. Phosphorus supports root development and flowering. Potassium improves overall plant health and disease resistance.
What NPK ratio is best for foliage plants?
Foliage-focused plants (pothos, monsteras, philodendrons, ferns) benefit from a higher nitrogen ratio — look for ratios like 3-1-2 or 2-1-1. These prioritize leafy growth over flowering. A balanced fertilizer (1-1-1) diluted to half-strength also works well for most tropical foliage plants.
Should I fertilize in winter?
For most houseplants, fertilizing in winter is unnecessary or even harmful. Most plants enter semi-dormancy during the shorter days of winter — growth slows dramatically and they can't process fertilizer effectively. The excess salts build up in the soil and can burn roots. Stop fertilizing in October/November and resume in March/April when you see new growth.
How do I dilute liquid fertilizer correctly?
Most liquid houseplant fertilizers should be used at 1/4 to 1/2 of the label recommendation for indoor plants. A typical dilution for liquid fertilizer is 5-10ml per liter of water. Always water your plant with plain water first, then apply the fertilizer solution. Never apply fertilizer to dry soil — it concentrates and burns roots.
What are signs of over-fertilizing?
Salt buildup from over-fertilizing shows as white crusty deposits on the soil surface or pot edges, yellowing leaves, brown leaf tips, and wilting despite adequate watering. If you suspect salt buildup, flush the soil by running plenty of plain water through the pot until it drains clear. Let it dry slightly before normal watering resumes.