Demystifying the science of fertilisers.

There are many types of fertilisers on the market, but how do we know which one to choose?

What does Nitrogen (N) do for plants? Is there such a thing as too much Phosphorus (P)? Where does Potassium (K) occur naturally? What is a balanced fertiliser? The experts at Gro-Pak are here to help decipher the science of fertilisers.

Understanding the nutrients in fertilisers and their uses.

Fertilisers are classified based on the essential nutrients they provide: nitrogen (N), phosphorus (P), and potassium (K). These three nutrients are known as the macronutrients and are represented by the NPK (2:3:4) ratio on fertiliser packaging. Here's a breakdown of different fertilisers based on their nutrient content and the best options for flowers, vegetables, and lawns.

1. Nitrogen-Rich Fertilisers

• Purpose: Nitrogen promotes leafy, green growth. It is essential for lawns and leafy vegetables.
• Examples: Urea, ammonium nitrate, and blood meal.
• Best For: Lawns and leafy vegetables like spinach and lettuce.

2. Phosphorus-Rich Fertilisers

• Purpose: Phosphorus supports root development, flowering, and fruiting.
• Examples: Bone meal, rock phosphate, and superphosphate.
• Best For: Flowering plants, fruiting vegetables like tomatoes, and root crops like carrots.

3. Potassium-Rich Fertilisers

• Purpose: Potassium enhances overall plant health, disease resistance, and drought tolerance. It also improves fruit and flower quality.
• Examples: Potash, potassium sulphate, and wood ash.
• Best For: Flowering plants, fruiting vegetables, and improving the overall health of all plants, including lawns.

4. Balanced Fertilisers

• Purpose: These provide a balanced ratio of N, P, and K, promoting overall growth.
• Examples: 10-10-10 or 5-5-5 (NPK ratios).
• Best For: General garden use, including vegetables, flowers, and lawns.

Best Fertilisers Based on Plant Type

1. Flowers:
• Best Fertiliser: A phosphorus-rich or balanced fertiliser (e.g., 10-30-10) to promote strong root systems and abundant blooms.
• Application Time: Early spring (August-September), just as flowers start to grow. A second application can be made in mid-spring.
2. Vegetables:
• Best Fertiliser: A balanced fertiliser or one slightly higher in phosphorus (e.g., 10-20-10) for fruiting vegetables, and a nitrogen-rich fertiliser for leafy greens.
• Application Time: Before planting in early spring and then side-dress during the growing season, particularly after the first fruit set.
3. Lawn:
• Best Fertiliser: A nitrogen-rich fertiliser (e.g., 20-5-5) to promote lush, green growth.
• Application Time: Early spring when lawns start to actively grow. A follow-up application in late spring or early summer ensures sustained growth.

Timing Based on South African Climates and Seasons

• Early Spring (August-September): This is the key time to fertilise as plants break dormancy and start growing. Apply nitrogen-rich fertilisers to lawns, balanced fertilisers to vegetables, and phosphorus-rich fertilisers to flowers.
• Late Spring to Early Summer (October-December): Consider a second round of fertilisation to support the growing season. For lawns, apply another nitrogen feed. For vegetables, especially fruiting types, a balanced or phosphorus-rich fertiliser works best.
• Autumn (April-May): Fertilise flowers and lawns lightly to prepare for the cooler months. Use a potassium-rich fertiliser to enhance cold resistance.
• Winter (June-July): Fertilisation is typically not necessary as most plants are dormant. However, in frost-free areas, you can apply a light feed to winter-growing vegetables.

Comparing liquid and pelleted fertilizers

When choosing between liquid and pelleted slow-release fertilisers, it's essential to consider their specific advantages and disadvantages and how these align with the needs of different types of plants and gardening environments. Here's an overview:

Liquid Fertiliser

Pros:

1. Quick Absorption: Liquid fertilisers are rapidly absorbed by plants, delivering nutrients almost immediately. This is particularly beneficial for plants that need a quick boost.
2. Easy Application: They can be easily mixed with water and applied through watering cans or hose-end sprayers, ensuring even distribution.
3. Customisable: You can adjust the concentration to meet specific plant needs, and it’s easy to apply as often as needed.
4. Suitable for Foliar Feeding: Liquid fertilisers can be applied directly to the leaves for quicker absorption, which is especially useful for nutrient deficiencies.
5. Good for Frequent Feeding: Ideal for plants that require regular feeding, such as flowering plants or vegetables during their growth period.

Cons:

1. Frequent Application Needed: Because liquid fertilisers are quickly absorbed, they need to be applied more frequently, often every 1-2 weeks, depending on the plant’s needs.
2. Leaching Risk: There’s a higher risk of nutrients being washed away, especially in sandy soils or after heavy rains, leading to potential nutrient loss.
3. Short-Lived: The effects of liquid fertilisers don’t last as long as those of slow-release types, requiring more consistent attention and reapplication.

 Pelleted Slow-Release Fertiliser

Pros:

1. Long-Lasting: Pelleted slow-release fertilisers gradually release nutrients over time, often lasting several months. This reduces the need for frequent reapplication.
2. Low Maintenance: Ideal for gardeners who prefer less frequent maintenance, as a single application can support plants over an extended period.
3. Reduced Risk of Overfeeding: The slow release of nutrients minimizes the risk of nutrient burn, which can happen with more concentrated liquid fertilisers.
4. Even Nutrient Distribution: Provides a consistent supply of nutrients, which is particularly beneficial for plants with steady nutrient needs.

Cons:

1. Slower Initial Effect: Since nutrients are released gradually, there is a delayed impact, making it less effective for plants needing an immediate nutrient boost.
2. Higher Initial Cost: Slow-release fertilisers tend to be more expensive upfront compared to liquid options.
3. Less Control: Once applied, it's difficult to adjust the nutrient levels if plants show signs of deficiency or excess.
4. Not Ideal for All Plants: Plants with short growing seasons or those needing quick nutrient uptake may not benefit as much from slow-release fertilisers.

Best Uses by Plant Type

1. Potted Plants:
• Best Fertiliser: Liquid Fertiliser. Potted plants benefit from the quick absorption and easy adjustment of liquid fertilisers, especially since they have limited soil to draw nutrients from.
• Pelleted Slow-Release Fertiliser can also be used for low-maintenance feeding, especially in larger containers.
2. Flower Beds:
• Best Fertiliser: Pelleted Slow-Release Fertiliser. Provides consistent nutrients over the growing season, reducing the need for frequent applications. For flowering plants needing a quick nutrient boost, a combination of both liquid and slow-release can be ideal.
3. Indoor Plants:
• Best Fertiliser: Liquid Fertiliser. Allows for controlled feeding, which is important for indoor plants that may not require large amounts of nutrients. It also minimizes the risk of over-fertilisation in a confined space.
4. Vegetable Gardens (Raised and In-Ground):
• Best Fertiliser: Combination of Both. Use liquid fertilisers for quick nutrient uptake during key growth stages (e.g., flowering, fruiting) and pelleted slow-release fertilisers to maintain a steady supply of nutrients throughout the growing season.
5. Lawn:
• Best Fertiliser: Pelleted Slow-Release Fertiliser. Lawns benefit from the even, long-term release of nutrients, which supports consistent growth and reduces the need for frequent fertilisation. Liquid fertilisers can be used for a quick green-up in early spring or to address specific nutrient deficiencies.

Like tools, nutrients have their dedicated jobs. This guide can help you choose the correct fertiliser to achieve your gardening goals!