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Potassium Deficiency
Problem: Older leaves turn yellow then start getting dark, scorched lesions around the edges of the leaves. Plants may stretch and stems may become weak. The symptoms are very similar to an iron deficiency except the tips of the leaves curl as the edges burn and die. The last picture below has some more information about the potassium requirements of your marijuana plant.
Solution: Potassium isn't absorbed properly when there is too much calcium or nitrogen in the system. Check the pH of your water, and flush your whole system with water that contains half the normal amount of nutrients and see if your plant starts showing signs of improvement.
Picture:
Big Symptom Picture:
Leaf Color:
Edges Appear Brown or Burnt
Pale Color Leaves
Yellow Leaves - Lower, older leaves
Brown or Dark Spots
Leaf Symptoms:
Lower Leaves / Older Growth Affected
Leaf Edges Appear Burnt
Leaf Tips Appear Burnt
Leaf Tips Die
Spots
Old Leaves Dropping Off
Slow Growth
Twisted Growth
Abnormal Growth
Leaves Curl Under
Leaves Curl Upwards
Plant Symptoms:
Old Leaves Dropping Off
Slow Growth
Twisted Growth
Leaves Curl Under
Leaves Curl Upwards
Stretch (big spaces between nodes)
Too Tall
Other Symptoms:
Buds Not Fattening
