Kelp fertilizer is a plant supplement made from marine algae, usually brown seaweed such as kelp species harvested from coastal waters. It is sold in liquid, powder, granular, or extract form and is used in both indoor and outdoor gardening to provide trace minerals, organic compounds, and small amounts of plant nutrients.
Most kelp fertilizers contain relatively low levels of nitrogen, phosphorus, and potassium compared to conventional fertilizers, so they are commonly used as a supplement rather than a primary nutrient source. They may contain naturally occurring compounds such as cytokinins and auxins, which are plant hormones associated with cell division and growth regulation. Kelp products are also valued for their micronutrient content, including iron, manganese, zinc, and boron.
In container growing, kelp fertilizer is often applied during active growth or recovery from stress such as transplanting, heat, or drought. Product composition varies widely depending on seaweed species, processing method, and concentration, so nutrient analysis and application rates differ between manufacturers.
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