Garden Fertilizer Calculator
Take the guesswork out of feeding your plants. Calculate application rates for your garden size and see the actual elemental nutrients being applied.
Garden Fertilizer Calculator
Calculate how much granular fertilizer to apply to your garden area, and see exactly how much N-P-K you are adding.
Check the back of your fertilizer bag for this recommended rate.
Application Summary
Nutrients Actually Applied
Understanding N-P-K
Every bag of commercial fertilizer has three numbers prominently displayed on the front, such as 10-10-10 or 5-4-3. These represent the percentage by weight of the three primary macronutrients your plants need:
- (N) Nitrogen: Promotes green, leafy growth. Vital for foliage plants and the early vegetative stage of fruiting plants.
- (P) Phosphorus: Crucial for root development, flower formation, and fruit set.
- (K) Potassium: Supports overall plant health, disease resistance, and water regulation.
Why Actual Nutrients Matter
If you apply 10 lbs of a 5-5-5 organic fertilizer, you are not applying 10 lbs of nitrogen. Since the fertilizer is only 5% nitrogen by weight, you are actually only applying 0.5 lbs of pure nitrogen. The rest of the bag consists of organic matter, filler, and secondary nutrients (like calcium and magnesium).
Fertilizer Safety & Best Practices
- Always Soil Test First: You cannot know what your soil needs without a laboratory soil test. Applying phosphorus to soil that already has high phosphorus can lock out other nutrients and pollute local waterways.
- More is Not Better: Over-fertilizing causes "nutrient burn," literally dehydrating and killing plant roots due to high salt concentrations.
- Wear Protection: Always wear gloves, long sleeves, and a dust mask when broadcasting dry fertilizers to avoid skin irritation and inhalation.