When selecting a fertiliser, understanding the NPK ratio is key. This refers to the proportions of Nitrogen (N), Phosphorus (P), and Potassium (K), which are the macronutrients plants need in higher quantities.

Here’s what each nutrient does:

• Nitrogen (N) is a vital nutrient that supports lush, green foliage and plays a critical role in photosynthesis, helping plants convert sunlight into energy. It is especially important for leafy plants and those that grow quickly. A nitrogen deficiency may result in pale, yellowing leaves, stunted leaf growth, and an overall weak appearance in the plant. This deficiency is most noticeable in older leaves, as the plant will redirect nitrogen to new growth.
• Phosphorus (P) is crucial for root development, as well as the growth of flowers and fruits. It enhances a plant’s ability to store and transfer energy, which is vital during flowering and fruiting stages. A phosphorus deficiency often results in poor flowering or fruit production, inhibited new growth, and reddish or purple discolouration on older leaves, especially in cooler conditions. This can significantly impact a plant’s long-term health and productivity.
• Potassium (K) is essential for strengthening a plant’s overall health, enabling it to fight off diseases, pests, and environmental stressors like drought or extreme temperatures. It aids in the regulation of water movement within the plant and supports the production of strong, healthy tissues. A potassium deficiency often appears as yellowing between leaf veins, browning or curling leaf tips, and a general decline in the plant’s vigor. Plants lacking potassium can become more susceptible to external threats.

An NPK ratio might look like 10-10-10, representing a balanced fertiliser, or 15-30-15, tailored for flowering plants.

Micronutrient Importance

Beyond NPK, a good fertiliser includes trace elements, or micronutrients, like iron, manganese, boron, copper, and zinc. These are required in smaller amounts but are equally crucial for overall plant health. If the label doesn’t specify these nutrients, it’s likely an incomplete fertiliser, which means your plants may not receive everything they need.

Now that you understand the building blocks of fertilisers, choosing the right one for your plants depends on factors like convenience, nutrient delivery speed, and whether you're fertilising indoors or outdoors.

Slow-Release Fertilisers

Slow-release fertilisers, available in pellet or coated forms, are designed to release nutrients gradually over a period of several weeks or even months. This slow-release process ensures that plants receive a steady supply of essential nutrients without the need for frequent reapplication. They are particularly popular for outdoor use, where they can support sustained plant growth with minimal effort. However, indoor plant care can be more challenging with slow-release fertilisers, as fluctuations in temperature, humidity, and watering schedules can impact the rate at which nutrients are released. These nutrient-rich fertilisers break down naturally, providing a gentler feed while reducing the risk of over-fertilisation, which can damage the sensitive roots of potted plants.

Liquid Fertilisers 

Liquid fertilisers are fast-acting and ideal for delivering immediate results, making them a popular choice for gardeners who want to see quick improvements in plant health. These fertilisers are either diluted in water or applied directly to the soil, allowing plants to absorb nutrients rapidly as they take up water. This makes them particularly effective during critical growth phases, such as flowering or fruiting. However, they require precise measurement and careful application, as over-fertilising can burn plant roots or leaves, causing more harm than good. Regular monitoring of plant needs and proper dilution is key to achieving the best outcomes with liquid fertilisers.

Synthetic or Mineral Fertilisers 

Synthetic or mineral fertilisers offer precise ratios of macro- and micronutrients, typically in a highly concentrated form. These fertilisers are manufactured to deliver nutrients efficiently and are particularly useful when plants need a quick boost. While the term "synthetic" often carries a negative connotation, it’s important to note that plants absorb these nutrients in the same way they would from organic sources. For instance, nitrogen from a synthetic fertiliser and nitrogen from compost are chemically identical to a plant. Synthetic fertilisers are especially effective for fast-acting results and can be tailored to specific plant needs. However, overuse can lead to nutrient imbalances in the soil or environmental runoff, so they should be applied responsibly and in moderation.

Organic Fertilisers 

Derived from natural materials such as compost, manure, plant matter, or animal by-products, organic fertilisers release nutrients slowly, creating a lasting impact on both plant health and soil quality. These fertilisers not only provide essential nutrients but also improve soil structure, encourage microbial activity, and increase water retention. While their NPK (nitrogen, phosphorus, and potassium) values are often lower than synthetic fertilisers, they are gentler on plants and safer for the environment. Organic fertilisers are an excellent choice for sustainable gardening, and with regular use, they contribute to healthier soil over time. To maximise their benefits, opt for organic fertilisers that contain a balance of macro- and micronutrients to meet your plants' needs throughout their growth stages. 

Foliar Sprays 

Foliar sprays are a unique fertilisation method that allows nutrients to be absorbed directly through the leaves. This makes them a quick and efficient solution for addressing visible nutrient deficiencies, such as yellowing leaves caused by a lack of nitrogen or magnesium. Foliar sprays are especially useful when soil conditions prevent nutrient absorption, such as during drought or poor soil pH. They act as a supplement rather than a replacement for regular soil-based fertilisation, as plants primarily rely on their root systems for long-term nutrient uptake. For the best results, apply foliar sprays during the early morning or evening to avoid evaporation and ensure better absorption.

Plant location significantly affects fertiliser needs, as indoor and outdoor plants have very different access to nutrients. Understanding these differences is key to keeping your plants healthy and thriving. 

Indoor Plants 

Indoor plants rely entirely on you for their nutrients, as they don’t have access to natural elements like rain, decomposing organic matter, or sunlight in the same way outdoor plants do. During the growing season (spring and summer), use a nitrogen-rich liquid fertiliser every 2-4 weeks to promote active growth, vibrant foliage, and strong stems. Be sure to dilute the fertiliser according to the package instructions to avoid overfeeding, which can damage the roots. During dormant periods (autumn and winter), plants grow more slowly and need less feeding. Switch to an organic slow-release fertiliser with low NPK values to maintain soil health without encouraging unnecessary growth. Over-fertilising during dormancy can lead to nutrient buildup and harm your plant, so err on the side of caution.

Outdoor Plants 

Outdoor plants benefit from a wider range of nutrients thanks to natural sources like decaying organic matter, rainfall, and the surrounding ecosystem. However, regular fertilising is still necessary to ensure optimal growth, especially in depleted or poor soil. Slow-release and organic fertilisers work well for most outdoor plants, as they provide sustained nourishment over time. You can supplement this with occasional liquid fertiliser feedings during flowering or fruiting seasons to support the plant’s increased nutritional needs. Additionally, observe your garden's soil quality and plant health to adjust your fertilising schedule as needed. Mulching and composting can further enrich the soil and reduce the need for synthetic fertilisers, creating a more sustainable, nutrient-rich environment for your plants.

Fertilising doesn’t have to be complicated. By understanding what your plants need and choosing the right products, you can support their health and vitality year-round. Remember, healthy plants are not just about light and water; proper nutrition plays a vital role too.

If you’re unsure where to start, explore our full range of indoor plant care products, designed with simplicity and effectiveness in mind. Whether you’re looking for slow-release pellets or fast-acting liquids, we’ve got your plant care needs covered. For more tips, visit our blog or speak to our team for tailored advice.

Helpful Tip

If you’re transitioning to a new fertiliser or adjusting your plant care routine, monitor your plants closely to detect any changes in leaf colour or growth patterns. These subtle cues can provide valuable insights into their nutrient needs.