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 centre.
Look at your lawn. Take note if the yellow seems to appear in a circular pattern or if the discolouration 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 chelated iron or iron sulphate spray to the lawn if the yellowing is due to an iron deficiency. Grass blades streaked with yellow are typically experiencing iron deficiencies. For most iron treatments, simply spray it onto the grass; however, read the directions on your product for the best results.
Apply peat moss to the grass to turn it back to green if the yellowing is due to Take-All Root Rot. Grass with this condition will have both green and yellow grasses blended together, with the yellow grasses bearing black or brown roots. Apply one to two bales of peat moss per 93 square metres (1,000 square feet) of lawn to the affected areas. After application, water the grass until it is wet.
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 colour without any striping or green grasses mixed in.