How to Eradicate Johnson Grass? | A Multi-Year Plan

Eradicating Johnson grass means removing its underground rhizomes and applying repeat herbicide treatments over several growing seasons.

Johnson grass is one of the toughest weeds to eliminate because it fights from two directions at once — its rhizomes spread underground while each plant drops thousands of seeds that stay viable in the soil for years. Learning how to eradicate Johnson grass means addressing both the root system and the seed bank, and accepting that lasting control takes more than a single season. The strategy is straightforward: remove the underground pieces, stop the seeds, and stay after it until the energy reserves are gone. Identifying Johnson grass early — look for broad leaves with a prominent white midvein and tall seed heads that resemble a loose panicle — gives you a head start before the infestation builds momentum.

The Big Picture — Why Johnson Grass Keeps Coming Back

This weed survives because it stores energy in underground rhizomes that produce new shoots, and each plant can produce thousands of seeds before you notice. Cutting the top growth alone does nothing — the rhizomes simply send up new shoots. The Missouri Department of Conservation states that all plant parts, including rhizomes, must be removed for successful control. That means physically digging out underground pieces and preventing seed heads from forming. A single missed seed head can restart the infestation, so regular monitoring across the entire growing season matters. Tilling and repeated digging can expose rhizomes to the surface, but regrowth is common unless every piece is removed. This is why Johnson grass earns its reputation as a perennial problem — it fights back from below, year after year.

How To Remove Small Johnson Grass Patches By Hand

For small patches, hand-pulling or digging after rain is the most direct method. Wait until the soil is soft, ideally after a soaking rain, then use a shovel, hoe, or trowel to lift the entire clump and its root system. The goal is to remove as much of the rhizome network as possible. Work carefully — rhizomes break easily, and any piece left in the ground can produce a new plant. Broken stem and root fragments left in the soil should be dug up if the area is small enough to allow it. Remove all plant parts from the area and dispose of them in the trash, not the compost pile, because pieces of rhizome can regrow. Check the spot regularly for regrowth and dig out any new shoots immediately. This approach works best when you catch the infestation early, before it has time to build a large underground network. For isolated plants, spot-digging is efficient and avoids the need for herbicides altogether.

Herbicide Strategy For Larger Infestations

When Johnson grass covers a larger area, spot-spraying with a glyphosate-containing herbicide is the most practical approach. The Missouri Department of Conservation recommends a 2-percent glyphosate solution applied to the foliage when plants are actively growing in late spring or early summer. Active growth is critical — the plant needs to be taking up water and nutrients for the herbicide to travel down to the rhizomes. Use a hand sprayer or backpack sprayer for precise coverage, and avoid spraying desirable plants because glyphosate is nonselective and will kill any green plant it contacts. For very young Johnson grass, sethoxydim offers another option before the weed becomes established. The herbicide Certainty Turf Herbicide is also labeled for Johnson grass, with a mix rate of 0.75 ounce per 2 gallons of water per 1,000 square feet.

The key to long-term success is persistence. The recommended sequence — cut seed heads in early July, then follow with 2-percent glyphosate spot applications — must continue for three to four years to fully deplete the rhizome energy reserves. Letting any plant set seed resets the clock, so mowing or spot-treating throughout the growing season is essential. Common mistakes include spraying when plants are stressed from drought or heat, expecting a single treatment to finish the job, and spraying too broadly, which damages surrounding turf and ornamentals. Always wear long pants, boots, long sleeves, and gloves when applying herbicide, and follow all label directions. Glyphosate is nonselective, so precise spot application is critical — off-target drift can damage or kill the grass and plants you want to keep.