Nitrogen (N): Importance for plants, addressing nutrient deficiencies and proper fertilisation

Nitrogen deficiency causes yellowing leaves, slowed growth and, in severe cases, can kill plants. Learn to spot the first symptoms and take action in time, before a nitrogen deficit affects your harvest.

The importance of nitrogen for plants lies primarily in the fact that it is essential for the production of amino acids, from which they make proteins. Nitrogen is also a component of chlorophyll, the green pigment that enables photosynthesis. Along with phosphorus, potassium, calcium, magnesium and sulphur, nitrogen is classified as a macronutrient, meaning a nutrient element that plants consume in the greatest quantities.

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Nitrogen deficiency in plants

Nitrogen deficiency first appears on older leaves in the lower parts of the plant. This is because plants can redistribute nitrogen as needed and, in the event of a deficiency, move it from old tissues to newly developing shoots. The leaves initially turn light green, then yellow from the tip towards the centre, and eventually dry out completely. If you do not intervene, the symptoms will spread upwards towards the tip and the plant will eventually die. Plants affected by nitrogen deficiency grow more slowly, have smaller leaves and may develop purple stems and leaf petioles.

• light green colour
• yellowing leaves starting in the lower parts
• slow growth
• purple stems and leaf petioles

You are most likely to encounter nitrogen deficiency during the vegetative phase, when plants need it most. As plants transition into flowering, their nitrogen consumption decreases and their requirements for phosphorus and potassium increase. Excess nitrogen can also be harmful, manifesting as a dark green colour, excessively vigorous growth or even burnt leaf tips.

How to provide plants with nitrogen

The fastest way to provide plants with nitrogen is in the form of water-soluble nitrates (NO₃). Urea and other insoluble forms of nitrogen must first be broken down by microorganisms in the soil, so their effect appears later.

• growth fertilisers
• organic fish emulsion fertiliser
• single-component nitrogen fertiliser

Remember that fertilising plants should always correspond to your growing method and substrate. When growing outdoors in soil (in beds), we recommend using organic fertilisers, such as fish emulsion, to replenish nitrogen. They are gentle on soil microorganisms. Mineral fertilisers should only be used for indoor growing, in pots, in hydroponic systems and in coco coir substrates, and outdoors only when necessary.

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Nutrient deficiencies can have many causes, and addressing them correctly requires at least a basic understanding of the principles governing plant nutrition. You can find further advice and guides for indoor and outdoor growers on the higarden blog.