Adjust pH to Correct Range
Give the Right Nutrients
Take Good Care of the Roots
Make sure that the iron deficiency starts to clear up within a week or more. The yellow leaves from before may not recover completely, especially if there was a lot of damage, but when new growth is coming in green, you know you’re good.
NOTE: Sometimes a cannabis iron deficiency (like all nutrient deficiencies) can be triggered by stressful conditions, and the plant may recover on its own after the period of stress is over.