nitrogen toxicity in weed

Nitrogen Toxicity & The Cannabis Plant

Published : Aug 9, 2017
Categories : Cannabis cultivation

It is possible to kill cannabis with kindness if you give your plants too much nitrogen. Identifying nitrogen toxicity makes sure you don’t go overboard and do more harm than good. Ensure happy and healthy plants by knowing what to look for when there has been a nitrogen overload.


The clichè “too much of a good thing” is never more true than over-loving your plants with nitrogen. Nitrogen is an essential element in the whole lifecycle of the cannabis plant. However, it can be a toxin if you are too heavy handed. In ideal quantities nitrogen is an essential building block of plant life ensuring vibrant and healthy growth. Giving too much nitrogen in an effort to boost plant growth instead leads to quick deterioration and very sick looking ladies.


The rapid growing cannabis plant needs a considerable amount of nitrogen during the vegetative phase. It is quite difficult to overdose with nitrogen using contemporary commercial fertilizers that are the result of years of experience. You will know you have nitrogen toxicity when:

  • * Leaves become deep dark green.
  • * Leaf stems may turn purple.
  • * Leaf tips will first turn yellow then burn.
  • * Leaves will claw. In some species leaf tips will bend horizontally at 90° then claw. If left untreated clawing will get worse, the leaves will yellow, die then fall off.
  • * Leaves will bowl or cup.
  • * Heat and pH issues will amplify the problem. Plants become less resilient to stresses when suffering toxicity.
  • * Seedlings will stress, become dark green and slow in growth.

Leaf clawing and cupping is also a symptom of over-watering. However, with overwatering leaves become dull and lack lustre. With nitrogen toxicity they become glossy and dark green.


Indoors or outdoors it is always recommended to avoid soils with time release fertilizers. They can cause toxicity during the flowering phase when cannabis requires little to no nitrogen.
Always follow manufacturers instructions when using commercial nutrients. Modifying nutrients and making hot mixes “to speed things up” will only lead to heartbreak.


The easiest thing to do is reduce the amount of nitrogen your plants are getting. Don’t use such strong mixes of nutrients. Be careful when measuring. Make sure you are following the manufacturers instructions. Often 3/4 strength nutrient mixes are better than full strength. Flush the plants out with pH balanced water then resume with a weaker mix. When plants have recovered resume regular watering routine. Affected leaves won’t recover and will still dry out. Remove them to avoid mold problems.

Tryng to speed things up by over feeding nitrogen to your cannabis can cause toxicity.

Nutrient Burn In Cannabis Plants

Nutrient burn can affect cannabis during any stage of growth. Prevention, identification, and remediation are all essential pieces of knowledge in the cannabis grower’s arsenal.



Nutrient burn in cannabis could be called the “novices lament” or “over-enthusiasm backlash.” Nutrient burn is a type of stress caused by overfeeding your plants or mixing nutrients too strongly. Novice growers are often under the misconception that more is better. This is very untrue. Often, burning can be caused by simple human error. Luckily, the condition can be fixed before it demolishes your crop. That said, it can damage a crop at any stage of its development.

Unlike animals (humans included), plants don’t put on weight when you overfeed them. After all, plants are a whole different order of organism. They require a balanced and ongoing series of chemical reactions to survive and thrive. Trying to fatten them up with extra feeding is the fast track to disappointment.

Nutrient burn can be caused by:

  • Mixing nutrients stronger than recommended during any phase of growth
  • Overwatering; plants need a dry period to function properly and access oxygen
  • Using bloom boosters too often or in too high a concentration
  • Using growth stimulants too regularly, causing dwarfism and burning due to excessive nutrient uptake


Nitrogen is the predominant compound found in cannabis nutrients, especially during the vegetative phase. Nitrogen toxicity will be quickly followed by more severe symptoms.

Early indications of nutrient build-up prior to burning can be:

  • Very deep green leaves
  • Bright, Day-Glow green, almost fluorescent tips
  • Leaf tips bent at 90°
  • Stalks and branches will become deep red, magenta, or purple
  • Sugar leaf and calyx tips will turn yellow, then dieback. Unlike the appropriate dieback of leaves during flowering, overfed bud leaves will remain engorged while they yellow, then dieback quickly and crisply

Further indications of nutrient burn are yellow, burnt tips on leaves. This will be widespread as over-fertilisation affects the whole plant. Small, burnt tips are common and nothing to worry about. When the yellowing intensifies and advances, however, it is time to take action. Once leaves start to curl and go brown, they are definitely goners.

Nutrient burn can be gradual if the overdose is only slightly stronger. It can also be rapid-appearing, progressing over a few days. The worst-case scenario is a chronic overdose that causes crop-wide yellowing and wilting overnight with leaf curl and lack of turgidity. In this case, if during the vegetative phase, start again. Recovery may be impossible or take longer than restarting completely.

Buds can be affected by nutrient burn as well. During the flowering phase, cannabis changes the way it uses nutrients. The need for nitrogen drops almost to zero while the demand for other compounds like calcium and magnesium increases. An overdose of any kind of additive will cause the same type of burning features.


Once your plant’s woes have been identified as nutrient burn, carefully remove all the damaged material. Break off all the damaged leaves. Trace calyx clusters back to their branch and remove the whole florette, just to be sure. Dead flowers and leaves will rot. As soon as possible, flush your growing medium out with clean, pH balanced water. If you are growing with a reservoir, measure the contents with a pH/EC meter and adjust with fresh water.

If you are mixing daily by hand, then calm down tiger, less is more with cannabis. Keep in mind that satisfactory results can be obtained with just plain water for the whole life of the plant.

Prior to returning to a regular feeding schedule, use a specialised plant tonic to nurse the plant back to health. The root biosphere will have been affected, as well as the green parts of the plant. Tonics with silver nitrate, humic and fulvic acids, vitamins and minerals are ideal to restore plants to health.

When returning to regular feeding, use only ¾ strength to avoid burning again. Plants will quickly regain their vigour and continue to grow strongly. Remember to adjust the growing period to allow for time lost when the plants were ill. Adding time to the vegetation photoperiod will not harm the plants. If the burning happened during flowering or with autoflowering strains, then you will just have to take the lower yield on the chin.


Prevention is always the best policy, so it is a bright idea to develop good habits that decrease the chances of mistakes. First of all, be sure to use the correct nutrients for the appropriate growth stage. Even then, it is a wise idea to only use ¾ the recommended dosage on product packaging. Sometimes, manufacturer recommendations can run things a bit “hot,” which leaves little room for error.

Use an EC/pH meter to check nutrient strength every time, whether hand mixing daily or in hydro reservoirs. Be sure to flush hydroponic systems, grow mediums, and soils to prevent salt build-up in the root zone.

Over-enthusiasm with nutrients can burn marijuana plants. Knowledge is power when it comes to big buds. So, how to prevent and treat nutrient burn? ]]>