Why is my grass green on top but brown underneath? 5 common causes explained

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There are many reasons why your grass has developed brown patches within the bottom inch of the grass blade while the rest of the plant remains green. This can be mistaken for dead grass however this generally isn’t the case as the top section of the blade is green.

It’s normal for a lawn to contain some brown grass. It’s only when it looks like the balance is tipping towards the brown end of the spectrum rather than the green end that we need to take action.

Identification of the brown patches can be tricky due to the many reasons that can lead to this condition including fungus, grubs, watering, drought, grass nutrition. This article will explain why these can cause problems as well as how to counteract them. It will also explore whether brown grass can turn green again.

Let’s explore the possible causes.

Fungus

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To see if some of the grass blades are affected by a fungal infection, you will have to get down on your knees, pull apart the grass and check the lower sections of the blades for black spots. Using a magnifying glass may make this job easier.

A common fungus that can attack ryegrasses is Bipolaris sorokiniana. It produces black spots across the grass blade. In particularly bad infections, the black spots will move towards the root and rot it until the grass dies.

Most fungal infections won’t kill the grass completely and the problem is purely aesthetical.

If you feel that the fungal infection is particularly bad during a growing season, try scarifying the lawn in the fall to reduce the thatch present just above the soil level. This will reduce the breeding ground for such fungal pathogens and allow more air to circulate the grass plant as well as penetrate down to the roots.

Lawn fungicides are available such as BioAdvanced Fungus Control for Lawns that will help keep the infection under control. Apply the lawn fungicide in spring, summer, or fall – essentially whenever the fungus is prevalent and the grass is growing. Fungicides usually take effect after 24 hours of application and once the blade and root have managed to recover your lawn will return to a beautiful shade of green.

Over-watering

Although watering is an important part of general lawn care, over-watering a lawn can also lead to a build-up of brown grass developing around the base of the grass base.

There are three main reasons why over-watering can cause your grass to turn brown.

Encourages insect infestations

Over-watering grass will discourage the grass from developing long deep roots as water will always be available at a shallow depth causing the roots to stay at a shallow depth. A shallow-rooted grass plant is susceptible to insect damage as the younger, softer roots are available at a depth that is the natural habitat of bugs. These soft roots are the food source of these insects and once they have damaged enough of the roots, it will lead to dead grass. If you feel that insects are causing an issue on your lawn please read our guidance on some common lawn pests.

Develops thatch

Thatch is the natural build-up of dead and decaying organic material that is brown in color. All lawns contain some amount of thatch however too much if it will begin swamp out the green grass of your lawn.

Over-watering will encourage thatch as the shallower roots grow laterally through the top layer of soil, the soil can develop a mat like consistency that will begin to build up with other organic matter, known as thatch. Thatch (and moss), as well as looking unsightly, will suppress the growth of your grass.

Fungal breeding ground

Over-watering can lead to consistent damp conditions at the soil surface. This is the perfect breeding ground for fungus to breed and spread. As mentioned earlier in this article, the fungus can attack your grass and turn brown.

As we can see, over-watering can turn a green lawn into a browner one. For tips on how to make sure that you don’t over-water your grass, feel free to read our helpful guide.

Lawnmower

Mowing your lawn is an essential part of lawn care however failing to look after your lawnmower can cause parts of your grass to turn brown.

One of the main reasons for this is using a lawnmower with blunt blades. Although a lawnmower with blunt blades will “cut” your grass, the way that it is doing this is by ripping the grass blades rather than slicing through them. As the mower rips through the blades, it will leave wounds on the grass.

After a day or two, these wounds will dry out and leave a partially brown and green grass blade. Inspect your lawn a couple of times every growing season to see if your grass is affected by this. If it looks like your lawnmower blades are in need of sharpening, you should be able to remove them by simply unscrewing the bolt that attaches them to the underside of your mower. Take these to a local hardware store or key cutter to get these sharpened.

Important – remember to double-check that you have securely reattached the mower blades once they have been sharpened.

It’s recommended that you should re-sharpen your mower blades once a year, preferably in the spring or early summer.

Fertilizer

Lawns with brown patches underneath the top level of grass can be a sign that the lawn contains weak plants that require food to boost its overall health.

One sure way of increasing the nutritional value of the lawn is to apply fertilizer. A weak grass plant is a sign that the root structure is short in length and has a thin consistency.

Fertilizers contain differing levels of three key macro-nutrients – Nitrogen, Phosphorus, and Potassium. These are known as the NPK value. Nitrogen promotes green leafy growth. Phosphorus will promote stronger root growth while potassium will improve the general functioning of the plant.

Before purchasing a fertilizer, check the NPK value on the packet. It is recommended that you apply a fertilizer containing phosphorus to encourage stronger root growth. This will, in turn, lead to a greener plant over time as the plant will become stronger and more resistant to all of the issues listed above.

It’s important that you apply fertilizer in the correct quantities and frequencies throughout the year. Its recommended therefore that you follow the instructions on the packet as overtreating a lawn can lead to dead turf. We have developed a useful guide with some advice on when and how often some of the most popular fertilizers should be applied.

Drought

We all know that turf requires water to ensure that it stays green. If the weather has been unusually dry and sunny for a week or two you may notice that areas of your lawn are turning brown, this may be a sign that you need to apply some water as soon as possible.

In normal conditions, you should only water your lawn once a week at most during the summer. During the spring you may not need to water it at all. Try to make sure that the water has penetrated the first four inches of the soil. In drought conditions, you may need to increase the watering to twice a week.

Try not to worry too much though as although the hot, sunny weather might have caused some of the green grass blades to turn brown, the lower part of the plant is probably still alive and the grass will recover once the weather has turned cooler again.

One way of telling if your lawn needs watering is the screwdriver test. To do this, try pushing a standard-sized screwdriver into the soil. If it is difficult to push the screwdriver into the first few inches of soil, it is probably time to water your lawn.

Can brown grass turn green again?

Absolutely. Grass is an amazing plant that can recover from all sorts of problems. Lawns may suffer from fungal, thatch, nutritional, compaction, and watering issues (to name but a few) but as long as it hasn’t completely died and you can still see some green shoots here and there, it will almost certainly recover in time. Do what you can to help it recover but in the end, just be patient and allow nature to take its course and you will have beautiful green turf once again.