Calculate the right amount of fertilizer for your garden based on area, fertilizer type, and application rate.
Proper fertilization is essential for healthy plant growth and abundant harvests. The three numbers on fertilizer packages (N-P-K) represent nitrogen, phosphorus, and potassium percentages. Nitrogen promotes leafy growth, phosphorus supports root development and flowering, while potassium enhances overall plant health and disease resistance. Calculating the correct amount prevents over-fertilization, which can harm plants and pollute groundwater, while ensuring your garden receives adequate nutrients.
| NPK Ratio | Best For | Application | Frequency |
|---|---|---|---|
| 10-10-10 | General purpose, vegetables | 4 lbs/1000 sq ft | Every 6-8 weeks |
| 20-20-20 | Fast-growing plants, containers | 2 lbs/1000 sq ft | Every 4-6 weeks |
| 5-10-5 | Flowering plants, bulbs | 4 lbs/1000 sq ft | Early spring, fall |
| 20-10-10 | Leafy vegetables, lawns | 3 lbs/1000 sq ft | Every 6 weeks |
| 10-20-10 | Root vegetables, transplants | 4 lbs/1000 sq ft | At planting, mid-season |
| 15-0-15 | Established lawns | 5 lbs/1000 sq ft | Spring and fall |
Sandy soils require more frequent fertilization as nutrients leach quickly, while clay soils retain nutrients longer. Conduct a soil test to determine existing nutrient levels and pH before fertilizing. Organic matter content affects nutrient availability and retention.
Heavy feeders like tomatoes and corn need more fertilizer than light feeders like beans and peas. Leafy greens benefit from high nitrogen, while fruiting plants need balanced or high-phosphorus formulas. Native plants typically require less fertilization.
Plants need more nutrients during active growth periods. Apply fertilizer in early spring when growth begins, and continue through the growing season. Reduce or stop fertilizing in late summer to allow plants to harden off before winter.
Heavy rainfall can wash away nutrients, requiring additional applications. Hot, dry weather increases nutrient uptake. Avoid fertilizing during drought stress or extreme heat. Water thoroughly after applying granular fertilizers.
Apply fertilizer when plants are actively growing and can utilize nutrients. Early morning application allows foliage to dry before evening, reducing disease risk. Avoid fertilizing before heavy rain to prevent runoff. Split applications into smaller, more frequent doses for better nutrient uptake and reduced waste.
Broadcast granular fertilizer evenly across the garden area using a spreader for uniform coverage. Side-dress row crops by applying fertilizer in bands along plant rows. Water-in granular fertilizers immediately after application. For liquid fertilizers, apply to soil rather than foliage to avoid burning.
Wear gloves when handling fertilizers and wash hands thoroughly afterward. Store fertilizers in a cool, dry place away from children and pets. Keep fertilizers away from water sources to prevent contamination. Follow package instructions carefully and never exceed recommended rates.
Compost provides slow-release nutrients and improves soil structure. Manure should be aged or composted before use. Cover crops add nitrogen and organic matter when tilled under. Mulching conserves moisture and adds nutrients as it decomposes.
Example: 20×30 ft vegetable garden with 10-10-10 fertilizer
Garden Area: 20 ft × 30 ft = 600 sq ft
Application Rate: 4 lbs per 1000 sq ft (medium rate)
Calculation: (600 ÷ 1000) × 4 = 2.4 lbs of fertilizer
Nitrogen: 2.4 × 0.10 = 0.24 lbs
Phosphorus: 2.4 × 0.10 = 0.24 lbs
Potassium: 2.4 × 0.10 = 0.24 lbs
Applications: 3 times per season (every 6-8 weeks)
Per Application: 2.4 ÷ 3 = 0.8 lbs