Explains how to correctly diagnose marijuana nutrient deficiencies.
Many problems are misdiagnosed so first check these other potential causes of problems before adding more nutrients.
First check the pH. If the pH is not in the range of 5.6-6.3 for hydro and 5.8-6.5 for soil, the cause of your problem is probably that a nutrient cannot be absorbed due to the irregular pH. Fix the pH first.
Check also that your problem is not over or under watering. An over watered plant starts off with leaf tips and stems that droop down (from the weight of the excess water). If the over watering goes on, the leafs will start to look yellow – mimicking the symptoms of a nutrient deficiency. An under watered plant is very easy to diagnose. If the growing medium is dry and the plant looks limp and lifeless, it needs water.
If your plants are over fertilized they will start to turn a darker green, wilt, and the leaves will thicken and start to resemble crepe paper. If you see these signs you should stop fertilizing for a while. If the problem gets more serious the leafs will begin drying out. You may have to flush by adding water to your pots until it runs out the bottom to get rid of the excess build up of fertilizer.
The wrong temperature or humidity can cause problems that might like a nutrient deficiency. Temperatures below 40ºF (4ºC) will cause damage to the plant tissue. Humidity that is drier than 40-55% will result in wilt and necrosis of leaf tips.
To diagnose your plants, first rule out the causes listed above. Once other causes are ruled out, consult the chart below for nutrient deficiencies.
To narrow down the likely problem look for multiple symptoms. For example, if you have yellowing of older leaves it could be either potassium or nitrogen. Yellow older leaves combined with leaves falling off means its more likely a nitrogen than potassium deficiency. Yellow older leaves combined with leaves curling under means its more likely a potassium than nitrogen deficiency. Multiple symptoms provide a more accurate diagnoses since symptoms are often the same for many different things.
Nitrogen, Potassium, Phosphorus and Magnesium are the most likely causes of problems since they get used the most.
Add the nutrients that appear to be deficient and wait a few days to see if the problems go away. You will likely need to monitor the new growth to see if the situation is improving.
Many of the symptoms such as leaves yellowing happen naturally in late flowering and should not be confused with a nutrient problem.
|Yellowing of young leaves||X||X|
|Yellowing of middle leaves||X|
|Yellowing of older leaves||X||X||X||X|
|Yellowing between veins||X|
|Old leaves falling off||X|
|Leaf curl over||X|
|Leaf curl under||X|
|Leaf tips burn on younger leaves||X|
|Leaf tips burn on older leaves||X|
|Young leaves wrinkle & curl||X||X||X||X|
|Necrosis (yellow and brown blotches and spots)||X||X||X||X||X|
|Leaf growth stunted||X||X|
|Dark green / purple leaves and stems||X|
|Pale green leaves||X||X|
|Hard / brittle stems||X||X|
|Growing tips die||X||X|
|Stunted root growth||X|