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Seaweed is a collective term for different types of algae and plants, that can be found in the sea. They can be recognized by the brown, green and sometimes red color. The use of seaweed as a fertilizer in horticulture, is not new. It has been used for decades. While in the early days, seaweed was collected from the coast, there is a wide range of products available that contain seaweed.  

The plant resistance can be improved by making use of seaweed. This, because essential minerals and trace elements such as phosphorus, calcium, zinc, sodium, iron, magnesium and sulphur are involved. Besides, the common seaweed ascophyllum nodosum, contains glycine betaine. It was proven that glycine betaine augments the plant resistance, especially in times of abiotic stress such as drought stress or high concentrations of sodium. Because our summers keep getting dryer, seaweed could be a solution. Moreover, a lower chance at mould around the plant’s roots could be a result of a ‘dryer’ way of cultivation.

However, this is not the complete reason for the success of seaweed. Natural elements for growth, vitamins, amino acids and enzymes can be found in seaweed. All of these elements are used by the plant to strengthen its resilience. As a possible result, the production of larger fruits or buds. Because seaweed contains different trace elements, the fertility of the soil is improved at the same time.

Seaweed is not seen as a fertilizer, often leading to the opinion that it does not add anything to the plant’s growth. However, seaweed complies with the theory of the “missing elements” and has several positive effects on both the plant and the soil. 

• Strengthening of the plant cells
• Improvement of the soil’s structure and water absorption
• Optimization of photosynthesis
• Stimulation for growth of fruits
• Stimulation for the soil life already present
• Positive effect in times of drought
• Rises the pH value of the soil in a short time
• Decreases chance for deficiencies, because of the improvement of the intake of nutrients (especially iron and manganese)

Components that can be used by the soil life (worms, mycorrhiza, etc.) as source of nutrition, can be added to the crop by making use of seaweed. Because of this, many products that contribute to a better soil life, which is also called inoculating, contain seaweed. 

Seaweed can be added through foliar fertilizing, through the solution in the fertilizer tank or it can be added to the planting pot directly. The best way of application, depends on the product. 

At last, always keep in mind organic material, such as seaweed, should not get in contact with disinfectants and the corresponding techniques. This, because it could lower the functioning of the organic products. 

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