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Nitrogen and cannabis plants

Nitrogen is a vital element for both plant and animal life. It fulfils a number of important functions in the overall metabolism of a plant and is essential for the manufacture of chlorophyll.

Nitrogen is relatively common in the universe; the sun and other stars contain a lot of it. It is the fourth most common element, based on weight, in the Earth’s crust. The brown-red colour of Earth is caused by nitrogen. Nitrogen has been used as in agriculture since prehistoric times and today is still the cheapest, most common, and most important soil supplement we make use of.

In general, nitrogen is not very easy for the plant to take up. Only if it’s in the right forms and under the right conditions can it be taken up sufficiently by the roots.

Soil seldom contains too little nitrogen, but it is possible for it to be present in adundance in a form that is not available to the plant. The availability of nitrogen is strongly dependent on the pH; in acid soils there it is normally enough available nitrogen present.

Nitrogen deficiency

Cannabis is very efficient at taking up nitrogen and under normal conditions has little trouble from nitrogen deficiency, with the exception of during a fast growth spurt or when the plant is severely stressed. There can be temporary symptoms of nitrogen shortage that simply go away of their own accord, without the need for your intervention. These symptoms are not damaging to the yield.

A nitrogen deficiency is characterised by a sharp yellowing of the young leaves and growth shoots between the veins. This mainly comes about because nitrogen in the plant is not very mobile. The young leaves cannot therefore draw nitrogen out of the older leaves when they need it. In cases of serious nitrogen shortage the older leaves and smaller veins in the leaf turn yellow.


  • Green-yellow colouration, from inside to outside, in the young leaves and grow shoots. The veins mostly remain green.
  • Yellowing increases, sometimes to the extent that the leaves are almost white; the bigger leaves also turn yellow. This stunts the growth.
  • In more serious cases, necrosis affects the leaf and the growth of the plant comes to a stand still.  


  • The pH in the root environment is too high is (pH> 6.5)
  • There’s a build up of high levels of zinc and manganese in the root environment
  • The nitrogen concentration in the root environment is too low
  • The root temperature is low
  • The medium is too wet thanks to which the supply of oxygen to the root stagnates
  • The root system is functioning badly thanks to being damaged, diseased or from roots dying off
  • There is to much light penetrating the feed water tub: light promotes the growth of algae (thereby using nitrogen) and breaks down nitrogen chelates

What to do

  • Light nitrogen deficiency symptoms are fairly easily reversible. The shortage is, depending on the cause, solvable by using various remedies. You can lower the pH, prevent an excess of manganese or zinc from building up, add nitrogen chelates to the substrates, improve the drainage or raise the temperature of the soil. Alternatively, a leaf nutrient containing nitrogen chelates can be applied. When growing on hydro a nitrogen deficiency in the plant, provided you use a good quality nutrient mix, is virtually impossible.
  • Go to your local grow shop; they can give you professional advice and the right products. A fertilizer with good composition contains more than enough available nitrogen.
  • Should a deficiency become apparent, adding nitrogen chelates to the soil is less effective and works more slowly than applying leaf nutrient. Essentially, to get 1 kg of nitrogen in to the roots requires adding 5 to 10 times as much nitrogen chelate. The nitrogen chelates have to be well mixed in to the soil because daylight breaks them down and the chelates have to be very close to the roots to be taken up.
  • The best thing to do is to spray the leaves with a watery solution of EDDHA (max. 0.1 gram per litre) or EDTA chelates (max. 0.5 gram per litre).


  • Spray the leaves during the hours of darkness (never in bright light).
  • 70-80% of the stated maximum dose is safer.
  • Test on a few leaves and wait 2 to 4 days; if the result is good then apply to the rest.
  • Improvement should be visible in 2 to 4 days (depending on the health of the plant).
  • The application can be repeated after a week.
  • Adding organic fertilizer such as cattle manure, chicken manure or mushroom compost to the soil, enriches it with natural chelates. But be cautious and avoid burning the plant roots by adding too much.
  • Special enzyme preparations break down dead roots so that new roots can be formed, while promoting the growth of friendly bacteria that live symbiotically with the plant. These protect the roots against fungal attack and make it possible for the plant to take up organically bonded nitrogen.


Plants need a lot more N during vegetative growth than they do during the majority of the flowering phase. It is not unusual to experience N toxicity in a garden, even for advanced growers. Certain strains (or even phenotypes) require significantly more or less of this nutrient than others.

A pH meter that has been neglected for calibration might also give you erroneous readings. Uneven light distribution may render certain areas N toxic as the leaves are unable to process this nutrient. Too much heat in the growing area can also cause excess water and nutrient uptake. Other causes of N toxicity include the addition of too much slow-release fertiliser amendments to soil.


Generally speaking, N toxicity is just a simple case of over-fertilisation of the base NPK macronutrients, which can be easily reversed. Symptoms include:

  • Dark green leaves: The lush and vibrant green foliage starts to darken into a very dull hue.
  • Clawing may occur: Tips of the leaves curl downwards. This is usually a sign of overwatering too, so use this indicator to troubleshoot.
  • Yellowing and browning: Leaves will eventually suffer from chlorosis and die if left untreated.
  • Random spots may appear, mimicking other deficiencies like Cal-Mag.


To remedy an N toxic environment is relatively simple:

  1. First, you must troubleshoot your conditions. Check your day temperatures, pH meter, and EC meter for calibration.
  2. Check for uneven waterings, so no particular plant is getting an excess, provoking wilting and clawing.
  3. Prepare a fresh batch of nutrient mix and be sure you are calculating values using the right parametric system (litres vs gallons, ppm vs EC). Reduce the amount of N given to the plants. This is usually done by adding half-strength the recommended amount of nutrients into the mix.
  4. Monitor the new growth. In a few days, the plant should resume healthy, vibrant green growth.