If your grass is turning yellow, it could be doing so for a few reasons. Certain nutrient deficiencies and diseases can cause your grass to turn from green to yellow. For instance, if your lawn is lacking iron or nitrogen, it could cause a yellow hue to take over your lawn. Certain fungus can also have the same effect on your grass. Fortunately, you can resolve most issues with help from products available at your local home and garden store.
Look at your lawn. Take note if the yellow seems to appear in a circular pattern or if the discoloration simply appears all over the lawn. If the yellowing is in a pattern, it could be due to a disease such as Summer Patch or Rhizoctonia Patch. Resolve Summer Patch by applying fungicide to the lawn, as the fungus Magnaporthe poae causes this problem. Resolve Rhizoctonia Patch, caused by the fungus Rhizoctonia cerealis, by watering your grass less, establishing adequate drainage for the soil and providing aeration for the soil.
Apply a nitrogen-iron product to your lawn if the yellowing is due to a nitrogen deficiency. Grass blades with this deficiency are totally yellow in color without any striping or green grasses mixed in.