Fertilizers are either organic — made from organic materials like livestock manure — or they’re inorganic, containing a range of synthesized chemicals. Inorganic fertilizers have more exact nutrient ratios and higher concentrations of nitrogen, phosphorus, and potassium (NPK), which provide an instant boost to gardens. However, they lack more than a dozen macronutrients necessary for ongoing growth. Organic fertilizers have lower amounts of NPK, yet they contain the important macronutrients missing from the inorganic formulas. Organics also have a lower chance of negative environmental impacts.

Water-soluble fertilizers are available in a crystallized form which is dissolved in water, or they come in a liquid form that requires further dilution before applying. They’re great for starter and mid-season fertilizing. If you want a slow release of nutrients into the soil, granular fertilizers provide that advantage. The manufacturer coats each granule so that it releases its nutrients over a two to three-month period. This type usually cost less, but their higher salt content can burn roots.

Kelp is a type of seaweed, and it's an efficient and effective organic fertilizer. Gardeners use it as a source of trace minerals due to its low ratios of NPK. It is available in meal, powder, and liquid form, but the meal is popular among gardening enthusiasts. To fertilize with kelp meal, spread it around the base of plants, shrubs, and flowers. You can also work it directly into the soil as a planting medium.

One of the most popular types of fertilizers is compost, a combination of carbon-based matter like dead leaves and sticks, and nitrogen-based green matter like kitchen waste or grass clippings. Not only does compost deter erosion and improve soil quality, but it also adds a variety of minerals and nutrients to it and increases protection against diseases and insect infestations. Plants growing in composted soil are better able to retain air, moisture, and nutrients and as a result, they are healthier.

Producers create organic bone meal from finely ground animal bones that were first steamed or cooked, so it’s not a viable choice for vegan-inspired gardens. Thanks to an abundance of calcium and phosphorus, though, bone meal is an excellent soil amender and feeds the microbes in the soil. It releases nutrients slowly, making it a great choice for gardeners seeking a long-term fertilizer. Bone meal doesn’t work for all soil pH levels, especially those with high alkalinity. Another drawback is that it can attract family pets like dogs.

Mild, organic, and fast-acting, fish emulsion fertilizer is rich in nitrogen, phosphorus, and potassium. The fish oil and fish meal industries create the thick concentrate from their byproducts. Growers who create their own compost can add it to the mix to increase its nutrient content. Fish emulsion is especially effective for leafy green vegetables or to give your lawn a healthy boost. Gardeners who have soil with high nitrogen levels should limit their use of this fertilizer to prevent nitrogen burn.

One of the three primary macronutrients in soil vital for healthy growth, nitrogen benefits the production of chlorophyll, which enables plants to convert sunlight into food. Plants are unable to take in nitrogen directly from the atmosphere, so it reacts with other compounds like ammonia, nitric acid, cyanide, and organic nitrates to form additional unique compounds that can. The overall wellness of a plant is dependent on nitrogen to enhance its biological growth processes.

This macronutrient plays a significant role in the plant’s reproduction and is essential for healthy root development, stem formation, flower production, and fruit growth. If the phosphorus levels are too high, they can stunt root growth. Too little phosphorus leads to leaf drops and weak flower stems. If you have flowering plants with buds that emerge but don’t open, your plants likely need additional phosphorus. Nonflowering plants usually don’t require extra phosphorus.

The entire plant makes use of potassium. While researchers know the effects of potassium on a plant, they aren’t sure why it works or how it is achieved. Potassium makes it easier for the plant to overcome disease, resist insect damage, or stand up to inclement weather conditions. If you notice a plant’s leaf margins or veins turning yellow or brown, or it develops weak flower stems and undersized buds, it’s likely suffering from a lack of potassium.

While nitrogen, phosphorus, and potassium (NPK) are the primary macronutrients that plants require, others play important roles in plant health.