What You Need to Know About Grass Turning Yellow

There are two main types of lawn diseases that homeowners face when they over-water their lawn. The first is true Stomatitis, which can be fatal to your grass if it is not treated quickly. This happens when the mycorrhiza (copper deposit) of the grass gets disrupted due to Phosphorus deficiency. Phosphorus is essential for the growth and distribution of oxygen in the soil. When the mycorrhiza gets damaged by Phosphorus deficiency, it dies and a yellow “canker” or pale green turf appears.


Stomatitis can occur in any lawn, but most often it occurs in cool weather when the soil is very dry. It attacks the underside of the blades of grass where the mycorrhiza lives. Canker often appears as yellow or orange patches on the blades. Both Stomatitis and Canker are caused by too much moisture being held in the lawn by Phosphorus. An easy way to prevent lawn diseases is to aerate the lawn as the seasons change. During the winter you should thin out the grass by removing some of the soil, making the grass healthier, then re-fertilize the lawn.


Another common lawn disease is Fescue. Fescue usually shows up as reddish-colored splotches on the blades of grass, especially near the base. This disease is also caused by Phosphorus deficiency but has an interesting cause. The Phosphorus deficiency starts in the spring when the turf comes out of its dormancy period. The grass blades do not get time to develop new mycorrhiza mycotoxins, which stunts grass development and causes Fescue.

Another way lawns become vulnerable to Fescue is from being turned yellow during the dormant season. If the lawn is turning yellow, particularly at the tips, it may be suffering from a fungal infection called Stomatitis. Stomatitis occurs when Phosphorus, lacking any oxygen, begins to oxidize. It usually attacks the grass blades and underside of the blades, causing yellowing and cracking. The fungus that causes this infection loves dry, shady areas, and can spread from one plant to all of your plants.

Phosphorus Deficiency

You can tell if your lawn is suffering from Phosphorus deficiency by looking at the mower blades. If the blades look yellow or brown, they may be infected with Phosphorus. In order to prevent turning yellow grass blades, it’s best to aerate your lawn in the spring, before turning it over in the fall.

Yellowish grasses, often referred to as pale green, are a sign of a more serious problem. Why is my grass turning yellow? The most likely culprit in this case is nitrogen, which is usually added to the soil to increase its water holding ability. When nitrogen levels drop below ideal levels, and it doesn’t get replenished, the lawn becomes prone to yellowing. If you’re unsure whether your fertilizer is high in nitrogen, you should contact your local nursery to find out how to test for this.

Another cause for turning yellow grass is phosphorous deficiency. Phosphorous is often added to the lawn to help maintain its health, but it often gets depleted from lack of usage. This is why grass becomes so dark green – because it has used up the phosphorus it needs. Because phosphorus is used up in the grass, this means the lawn is suffering from a deficiency in the nutrient that helps it grow.

Tips To Stop Grass Turning Yellow

There are several steps you can take to correct this deficiency. If you think you have a Phosphorus deficiency, it’s best to contact your local nursery to test for this and get instructions on how to correct your lawn’s deficiency. Most importantly, though, keep your grass growing and don’t give up if it turns yellow quickly – there may be an underlying deficiency that you didn’t even know about. You may just need to add a bit more fertilizer to make it grow back to its original pale green lawn color.