Comprehensive Guide to Fertilizers
Fertilizers are essential for supplying nutrients that plants need to grow, flower, and produce fruits and vegetables. Understanding the types of fertilizers, their application rates, and benefits is crucial for successful gardening. Below, we explore the most common fertilizers used in South African gardens, both organic and inorganic.
1. Organic Fertilizers
Organic fertilizers are derived from natural sources and improve soil structure while providing nutrients.
| Fertilizer | Main Nutrients (N-P-K) | Application Rate (g/m²) | Frequency | Benefits |
|---|---|---|---|---|
| Compost | Varies (Balanced) | 3-5 kg | Monthly | Improves soil structure, supports microbes, reduces waste |
| Manure (Cow/Chicken) | 1-1-1 to 3-2-2 | 2-3 kg | Monthly or seasonal | Slow-release nutrients, improves fertility, organic matter addition |
| Bone Meal | 3-15-0 | 50-100 g | Once per season | High in phosphorus for root development, flowering, fruiting |
| Fish Emulsion | 5-2-2 | 100-150 ml diluted per m² | Every 2-3 weeks | Fast-acting nitrogen, boosts leafy growth |
| Seaweed Extract | 0-0-1 (trace elements) | 100-150 ml diluted per m² | Every 2-4 weeks | Improves stress resistance, stimulates root growth, adds micronutrients |
2. Inorganic / Synthetic Fertilizers
Synthetic fertilizers provide nutrients in concentrated form for immediate uptake by plants. They are convenient but should be used carefully to avoid soil degradation.
| Fertilizer | Main Nutrients (N-P-K) | Application Rate (g/m²) | Frequency | Notes |
|---|---|---|---|---|
| Urea | 46-0-0 | 20-40 g | Every 3-4 weeks | Highly concentrated nitrogen source, good for leafy crops |
| Superphosphate | 0-20-0 | 50 g | Once per planting | Promotes root development, flowering, and fruit set |
| Potassium Sulfate | 0-0-50 | 30-50 g | Every 4-6 weeks | Increases fruit size, sugar content, and disease resistance |
| NPK 2:3:2 | 2-3-2 | 50-100 g | Every 4 weeks | Balanced fertilizer for general vegetable gardens |
| NPK 3:1:5 | 3-1-5 | 50-100 g | Every 4 weeks | Enhances flowering and fruiting, good for fruit trees |
3. Specialized Fertilizers
Special fertilizers target specific plant needs or soil deficiencies.
| Fertilizer | Use | Application Rate | Frequency | Notes |
|---|---|---|---|---|
| Magnesium Sulfate (Epsom Salt) | Corrects magnesium deficiency | 20-30 g/m² | Monthly | Improves chlorophyll formation, prevents yellow leaves |
| Calcium Nitrate | Prevents blossom-end rot in tomatoes and peppers | 50 g/m² | Every 3-4 weeks | Provides calcium and nitrogen simultaneously |
| Iron Chelates | Corrects iron deficiency (yellowing leaves) | 10-20 g/m² | Once per month | Especially for alkaline soils common in South Africa |
4. Fertilizer Tips for South African Gardens
- Check soil pH before applying fertilizers; many SA soils are slightly acidic or alkaline.
- Use slow-release fertilizers where possible to reduce leaching during heavy summer rains.
- Combine organic and inorganic fertilizers for both immediate and long-term nutrient supply.
- Adjust application rates based on crop type, growth stage, and seasonal rainfall.
- Always water after applying granular fertilizers to reduce burn risk.