Do red plants need more iron?
Iron primarily helps to create green chlorophyll pigment and not red pigment. However, red plants like scarlet temple or Ammannia gracilis can benefit from extra iron because many of them are also high light plants that consume more nutrients in general. Red-leafed plants contain large amounts of red pigment and smaller amounts of green chlorophyll, and scientists are looking into the purpose of these red pigments and why red plants become more vibrant in bright sunlight. Under intense lighting, the red pigment may serve to protect leaves from excess light energy, and the amounts of green pigment may be decreased since not as much chlorophyll is needed to collect light photons. For the aquarium hobby, we recommend a combination of high light, carbon dioxide (CO2) injection, and good nutrient dosing (including iron) to enhance the redness of your plants.
For more information about iron and when you need to dose it, read the full article here.