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Why Is Johnson Grass Bad? | 2 Shocking Reasons You Must Know!

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Johnson grass is one of those plants that frequently raise questions in people’s minds about their stature as being good or bad.

You may have heard supporting facts in favor of Johnson grass, but evidence also suggests that Jonson grass is bad for cattle.

So, what characteristics does this plant possess that have rendered it harmful? Why is Johnson grass bad?

While it has benefits, Johnson grass can be seriously harmful and even fatal for cattle when consumed more than the safe limit.

If the Johnson grass has taken over the fields or pastures in your area, you must learn about it and its potential threats.

For that, please keep reading!

Halepense grass picture—why is Johnson grass bad
Why is Johnson grass bad? – Image via Petr Ganaj.

Why Is Johnson Grass Bad? | Reasons & Solutions!

Why is Johnson grass bad? That is a question in every gardener and farmer’s mind, especially those who grow forage for grazing purposes.

There are two different aspects to the disadvantages and drawbacks of Johnson grass that make it an unsuitable plant.

One issue with Johnson grass is that it proliferates invasively, leaving little resources for other vegetation.

Another problem is with the chemicals in this plant. It produces harmful chemicals and elements that are known to kill animals, especially in specific situations like frost.

Let’s explore these in detail.

1. Invasive Nature

First, it is an invasive plant.

Johnson grass grows and spreads like fire.

That happens because this plant reproduces through seeds as well as rhizomes. Johnson grass produces a massive quantity of seeds and can quickly sprout from them to get into a mature form.

It produces anywhere from 30000 to 80000 seeds, which remain in a top position for up to ten years.

Even with rhizomes, this plant can grow in about 20 days after the seedlings come out of the ground. More than 250 stems are growing out of each of these plants in their underground portion.

This excessive seed production and dispersal means that Johnson grass is a weed that spreads over huge pastures and fields in no time. The rapid spread of this weed creates an issue when it takes over the resources of other plants growing in the same area.

“For example, water and fertilizer are added in limited quantities in the fields, and they are added for other important vegetation to grow properly.”

Lack of water and other important factors can lead to disproportionate growth of the plants.

Johnson grass contributes to this lack of resources needed as an invasive plant that grows everywhere and takes up most of the resources.

How to Control the Growth of Johnson Grass?

The excessive and unchecked growth of Johnson grass needs to be controlled as it threatens the diversity of plants and is not a very scenic view for the audience.

You can take certain recommended measures to keep the growth of this weed under check.

Related article: How to Get Rid of Johnson Grass in One Week?

You have to take steps and lay down measures to prevent the spread of seeds and the production of new ones.

  • Rhizomes must be attacked and killed before giving birth to new plants.
  • If there are any signs of infestation in the area, you should destroy them as soon as possible.
  • It has been found that mowing the field at regular intervals can reduce or at least limit the production of seeds by Johnson grass.
  • Avoid delaying harvesting the fields to ensure the seeds do not disperse far away.
  • Most Johnson grass infestation does not appear on high-quality grounds.
  • You will notice it taking over on compromised land, where controlling different varieties of vegetation is a bit difficult.
  • Here, you can spray a glyphosate solution as a herbicide on the weed to kill it off. Be careful not to spray too much or spray on other harmless plants in the area.
  • Adding the herbicide immediately or during the early stages of flowering is recommended.

That was about the invasive nature of Johnson grass.

Now, let’s talk about the poisonous part.

2. Poison and Intoxication

Why is Johnson grass bad, you say? It’s poisonous!

Johnson grass becomes the main fodder for cattle when other plants and vegetation die off.

Since Johnson grass is resistant to drought and can swiftly multiply, animals can consume large amounts of this plant, especially when there is a lack of other crops and vegetation.

If Johnson grass is ingested in large amounts, it can lead to several health issues for the cattle.

Animals may suffer from severe issues like nerve damage, and the grass may even kill the fetus in pregnant animals.

Poisoning caused by nitrates and cyanides in the grass is a primary risk for cattle.

Hydrogen cyanide or Prussic acid is produced in high quantities in Johnson grass, especially during certain environmental conditions such as dryness, drought, frost, etc.”

I recommend keeping your cattle from feeding on any place with Johnson grass until at least 7–8 days after the frosting period, as cyanide and nitrate levels are slightly lesser then.

The exact amount of these poisonous materials will depend on the density and nature of the species of the Johnson grass.

How to Keep the Cattle Safe from Johnson Grass?

You can take certain measures to ensure the cattle are safe from this weed.

  • Prevention of the spread and growth of this plant should be the first step. Prevention can be done by using seeds free from weeds, sanitizing the equipment after it has passed through an infested area of Johnson grass, not running the equipment and machines over the place with seeds of this weed, and more such steps.
  • Herbicides and other chemical and mechanical methods help eradicate Johnson grass from the fields.

With that said, that was all about why is Johnson grass bad.

Here’s a video if you want to know more:

Why is Johnson grass bad? | Johnson Grass Management – Tips from a Wildlife Biologist – YouTube

Let’s move toward the conclusion.


I hope now you understand why is Johnson grass bad.

While initially, Johnson grass may be thought of as a good plant due to the apparent benefits, such as providing an alternate material for fodder, especially during tough times, such as frost and drought, when most other plants won’t survive.

However, the consumption and invasion of Johnson grass need to be controlled.

If taken in large quantities, Johnson grass can lead to several issues, such as nerve damage, cyanide and nitrate poisoning, and even death.

Moreover, the invasive nature of the weed takes away the resources to grow good vegetation.

Be careful when using herbicides and other chemicals as control methods. If grown in balance, Johnson grass might not be the worst.