Lawn Care: What's Causing Yellow Spots on Your Lawn & How to Fix It

Has your vibrant green lawn suddenly become tainted with yellow spots? These yellow patches on your lawn can be the result of several different factors. If you’re wondering what’s causing yellow spots on your lawn, wonder no more! Whether you have a small yellow patch or a large swath of yellow, here are a few reasons why, along with some ways to fix them.

Dryness

Excessively hot weather or having areas of your lawn completely exposed to full sun all day can dehydrate the grass pretty quickly. This heat stresses your lawn, causing damage and discoloration.

One solution to dryness is to water the turf more frequently and deeply, early in the morning if possible to allow the water time to dry over the course of the day. You can also consider reseeding in the fall to repair significant damage.

Excess Nitrogen

Your lawn can get excess nitrogen from two sources: overfertilizing and dog urine. Nitrogen is a chemical that enhances green leafy growth and is a necessary nutrient for a lush, healthy lawn. Too much nitrogen, however, can cause chemical burns to grass roots and a change in the pH of soil, leading to yellowing grass.

Dog urine also contains a high concentration of nitrogen and can cause burn spots on your lawn. Urine spots are often yellow bordered by greener grass because the diluted edges of the urine actually feed the grass (like fertilizer) while the more concentrated center of the urine spot burns the roots and causes the discoloration.

The best way to minimize damage from excess nitrogen is to prevent it in the first place. Use caution when fertilizing and make sure to water it in deeply when applied. If damage has already occurred, water the patch immediately to drain it and then water everyday for a week. Put in compost to replenish any lost minerals. If the grass is already dead, put sod over the area and reseed it the following season. Train your pet to urinate in other places and not go to the same spot repeatedly. Water any urine off your lawn immediately to minimize damage.

Disease

Most turf diseases that cause your lawn to have yellow spots are fungal. Temperature, thatch, and moisture levels all affect your lawn’s susceptibility to fungus. Some of the most common fungal diseases include fairy rings, snow mold, fusarium, and smut.

To help prevent fungal disease, make sure your lawn is dethatched and aerated. Try to water in the early morning hours so the moisture has time to evaporate throughout the day and not sit overnight. Make sure to also rake up any clippings, debris, and leaves to prevent moisture from being trapped underneath.

Nutrient Deficiencies

Nutritional deficiencies can lead to discoloration of your lawn. Nitrogen and iron are two of the most common deficiencies that cause yellow spots on your lawn. Nitrogen deficiencies cause leaves to turn yellow-green or yellow and your lawn will have stunted growth. Large collections of clover are also common in nitrogen-deficient lawns. Iron deficiencies will often cause the younger grass blades to turn yellow but don’t usually cause stunted growth. A soil test can indicate the deficiencies.

Once the nutrient deficiency has been identified, treat it with a nutrient specific plant food or fertilizer.

Pests

Discoloration of your lawn can also be caused by small insects chewing on grass roots causing damage. One way to check for this is to get a magnifying glass, part the grass blades, and thoroughly inspect the thatch for larvae or insects. Pest damage to grass is usually caused by younger pests and not adults.

Once you have identified the pests that are damaging your lawn, use an insecticide formulated for that pest to treat. Reducing thatch, irrigation, and proper fertilization can also help reduce pest populations.

Soil Compaction

Physical damage from frequent walking on the lawn can cause soil compaction where the soil gets packed so close together that the pores are too small. This restricts the roots and keeps them from spreading. Water and other nutrients also can’t penetrate the densely packed soil.

To help loosen the soil, aerate your lawn with either a core aerator or a rake. Follow the aeration with grass seed, fertilizer, and a layer of loam. Try to keep heavy traffic off the lawn. If that’s not possible, consider installing a walkway or stepping stones in high traffic areas.

RESTORATION

Now that we’ve identified some of the reasons your lawn has yellow spots and ways to fix them, how can you restore the vibrant green color? Here are some other tips to bring your lawn back to life.

Thin out trees so plenty of sunlight can get to the area (without allowing full sunlight exposure all day)
Maintain sharp mower blades and only mow when the grass is dry
Improve drainage of your lawn
Rake up any excess grass clippings and fallen leaves
Fertilize as recommended and watch for weed competitors which can deplete resources from your lawn
Utilize a professional lawn care service that can provide you with a free lawn analysis and lawn care plan