Organic or Inorganic fertilizer: Which is better?

Both organic and inorganic fertilizers provide plants with the nutrients needed to grow healthy and strong. However, each contains different ingredients and supplies these nutrients in different ways. Organic fertilizers work over time to create a healthy growing environment, while inorganic fertilizers provide rapid nutrition. Determining which is better for your plants depends largely on the needs of your plants and your preferences in terms of cost and environmental impacts.

Composition

Fertilizers supplement the soil with macronutrients needed in large amounts: nitrogen, phosphorous and potassium. However, organic and inorganic fertilizers do so via different materials. Organic fertilizers contain only plant- or animal-based materials that are either a byproduct or end product of naturally occurring processes, such as manures, leaves, and compost. Inorganic fertilizer, also referred to as synthetic fertilizer, is manufactured artificially and contains minerals or synthetic chemicals. For example, synthetic nitrogen fertilizers are typically made from petroleum or natural gas. Phosphorus, potassium and other trace elements in inorganic fertilizers are often mined from the earth. Balanced inorganic fertilizers, high in all three macronutrients, commonly include products like ammonium nitrate, ammonium sulfate, potassium chloride (potash), triple superphosphate, and magnesium sulfate (Epsom salts).

Nutrient Availability

Organic fertilizers release nutrients only when the soil is warm and moist, which tends to correspond with your plants’ times of greatest need. However, they rely on soil organisms to break down organic matter, so nutrients are released more slowly than they are from inorganic fertilizers. This slow-release method reduces the risk of nutrient leaching, but it takes time to supply nutrients to plants. In contrast, inorganic fertilizers provide this nutrition in plant-ready form immediately. However, the concentration of nutrients increases the risk of burning the plant, and the rapid release of nutrients may leach them deeply into the soil and water table where plants can't access them.

Application

The nutrients and exact elements available from an organic fertilizer, such as manure or compost, can only be guessed at without laboratory testing. This means you’re giving an inexact application that may or may not meet your plants’ needs. By comparison, applying inorganic fertilizers is simple, because the amount of a given element and the rate of application are known.

Cost

Organic fertilizers often cost significantly more than inorganic fertilizers, but over time, this extra cost may be outweighed by the benefits it provides. Organic fertilizers continue to improve the soil long after the plants have taken the nutrients they need. Therefore, the longer your soil is fed with organic fertilizers, the better its composition and texture. So, while inorganic fertilizer is cheaper in the short term, it adds less to the soil in the long term.

Environmental Impacts

Inorganic fertilizers are immediately available to your plants, but they are subject to leaching, a process that occurs when fertilizers are washed by rain or irrigation water below the level of plant roots. Heavy applications can burn your plants and build up toxic salt concentrations in the soil, which can create chemical imbalances. Organic fertilizer may also build up concentrations of some nutrients, but buildup of toxicity is unlikely as long as the organic material is able to fully decompose. In addition, because organic fertilizers are made from natural sources, only limited amounts of fossil fuels are used in production. This means greenhouse gas released into the atmosphere is lower in organic fertilizer production than it is in inorganic fertilizer production.