Lawn Problem Solver

Johnson grass

Sorghum halepense

Johnson Grass is a tall, aggressive grassy weed that spreads by seed and underground rhizomes. It grows much faster than turfgrass, forms coarse clumps, and can be difficult to control once established in lawns, landscape beds, fence lines, and bare areas.

Grassy WeedPerennialWeed
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Johnson grass

What Johnson grass Looks Like

Johnson Grass looks like a tall, coarse grass that grows much faster than the surrounding lawn. It has very wide leaf blades, thick stems, and can reach several feet tall if not mowed or removed.

Mature plants may produce large, open seed heads. One of the biggest identifying features is its thick underground rhizomes, which allow it to spread and regrow after mowing or pulling.

Why It Spreads

Johnson Grass spreads through both seed and underground rhizomes. Its often found in disturbed soil, thin turf, landscape beds, and areas where the lawn is weak.

Mowing can keep it shorter, but mowing alone usually will not eliminate it because the plant can regrow from underground rhizomes. If allowed to produce seed heads, it can spread even more aggressively.

How to Prevent It

Prevent Johnson Grass by keeping the lawn thick, healthy, and maintained. Mow before seed heads form, repair thin turf areas, and avoid leaving bare soil exposed where seeds can germinate.

In landscape beds, use mulch to reduce seed germination and remove young plants before they establish rhizomes. Avoid tilling or chopping mature Johnson Grass rhizomes into pieces, because small rhizome fragments can regrow.

Best timing: Spring through early summer before Johnson Grass gets tall and produces seed heads.

How to Control It

Control depends heavily on where the Johnson Grass is growing and what grass type you are trying to protect.

In landscape beds, cracks, fence lines, and non-lawn areas, a non-selective herbicide may be used carefully as a spot treatment according to the label. In lawns, selective control is more difficult because many products that injure Johnson Grass can also injure desirable turfgrass.

For established clumps, repeated treatments are often needed because the plant can regrow from rhizomes. Digging can work on small patches if the rhizomes are fully removed, but leaving pieces behind may allow it to return.

Best timing: When Johnson Grass is young and actively growing. Established clumps are usually easier to suppress with repeated treatments during active growth.

Recommended Solution

Johnson Grass is one of the harder grassy weeds to remove because it spreads underground. Start by identifying where it is growing. If it is in landscape beds, gravel, cracks, or non-lawn areas, careful spot treatment is usually the easiest approach.

If Johnson Grass is growing in the lawn, choose the correct product based on your lawn type. Some lawns have selective herbicide options, while others may require careful spot treatment. Mow before seed heads develop, avoid spreading rhizome pieces, and plan on repeat control because established Johnson Grass rarely disappears after one treatment.

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Frequently Asked Questions

What is Johnson Grass?

Johnson Grass is a coarse, perennial grassy weed that spreads by seed and underground rhizomes. It grows much taller and faster than most lawn grasses and can form aggressive clumps.

Why is Johnson Grass hard to control?

Johnson Grass is difficult to control because it can regrow from underground rhizomes. Even if the top growth is mowed or removed, pieces of the underground root-like stems can survive and send up new shoots.

Can I kill Johnson Grass without killing my lawn?

It depends on your lawn type and the herbicide being used. Some turf types may have selective control options, but many Johnson Grass treatments can also injure desirable grass. Always match the product to your turf type and label directions.