Johnson grass can produce serviceable hay with respectable protein levels, but it comes with a risk that most other hay grasses do not: the potential to poison livestock with hydrogen cyanide. Originally brought to the United States as a forage crop in the early 1800s, it fell out of favor so dramatically that multiple states eventually classified it as a noxious weed. Whether it makes “good” hay depends almost entirely on when you cut it, how you cure it, and what animals you plan to feed it to.
Why Johnson Grass Keeps Showing Up in Hay Conversations
If Johnson grass is so problematic, why does anyone bale it at all? The answer is sheer abundance. Johnson grass is aggressive, fast-growing, and nearly impossible to eradicate once it establishes itself. It spreads through both seed and underground rhizomes, and it thrives across the southern and central United States in roadsides, pasture edges, fence rows, and neglected fields. For many landowners, the choice isn’t whether to grow it; it’s whether to do something productive with a plant that’s already there. Cutting it for hay at least keeps it from going to seed and making the weed problem worse, and the bales can offset feed costs when managed carefully.
The grass also grows quickly enough to allow multiple cuttings per season, and in fertile soils it can produce impressive tonnage. Research on Johnson grass harvested at different growth stages shows that dry matter yield increases substantially as the plant matures from a young three-week regrowth stage through to later stages like dough formation.1PubMed Central. The impact of maturity stages on yield, quality, and nutritive value of ensiled Johnsongrass [Sorghum halepense (L.) Pers] So from a pure volume standpoint, it can be a productive forage. The trouble is that volume and quality pull in opposite directions as the plant ages.
Nutritional Quality Depends Heavily on Cutting Stage
Johnson grass that is cut young can be surprisingly nutritious. At a three-week regrowth stage and at the boot stage (just before the seed head emerges), the plant carries its highest concentrations of crude protein and total digestible nutrients, with the lowest fiber content. Once Johnson grass reaches the flower stage and beyond, fiber climbs, protein drops, and digestibility falls off. This same pattern holds across multiple harvests in a season.1PubMed Central. The impact of maturity stages on yield, quality, and nutritive value of ensiled Johnsongrass [Sorghum halepense (L.) Pers]
That means the window for making decent-quality Johnson grass hay is narrow. Cut it too early and you sacrifice yield. Wait too long and the hay is stemmy, low in protein, and less palatable. Most producers who intentionally harvest Johnson grass for hay aim to cut at or just before the boot stage, which balances a reasonable yield against acceptable nutrient levels. Hay cut from mature, headed-out Johnson grass is comparable in feed value to straw, and animals will often refuse it or eat it only reluctantly.
Compared to purpose-grown hay crops like bermudagrass or orchardgrass, well-timed Johnson grass hay can hold its own nutritionally. It won’t match the protein of a good alfalfa cutting, but it can serve as a maintenance-quality forage for cattle that aren’t in heavy production. The real question, though, is not whether the nutrient profile works on paper. It’s whether the poison risk makes it worth the gamble.
The Cyanide Problem
Johnson grass belongs to the sorghum family, and like its relatives, it contains compounds called cyanogenic glycosides. These are chemical precursors that can release hydrogen cyanide (also called prussic acid or hydrocyanic acid) when plant cells are ruptured. Under normal growing conditions, the concentration of these compounds in a healthy, mature stand of Johnson grass is usually low enough that grazing cattle can tolerate it. But certain stress events dramatically spike cyanide levels.
The situations that raise the danger include frost, drought stress, wilting after cutting, and herbicide application.2MSU Extension. Johnsongrass (P3205) Young regrowth after cutting is also higher in cyanogenic glycosides than a mature stand. This creates a catch-22 for hay producers: the young, protein-rich growth that makes the best hay is also the growth most likely to contain dangerous levels of cyanide precursors.
When an animal eats fresh Johnson grass containing high levels of these compounds, enzymes in the rumen break down the glycosides and release free hydrogen cyanide into the bloodstream. Cyanide blocks cellular respiration, meaning the animal’s cells can’t use oxygen even though the blood is fully oxygenated. Symptoms progress rapidly from labored breathing and staggering to convulsions and death, sometimes within minutes. Animals found dead in a Johnson grass pasture with bright cherry-red blood are a classic sign of prussic acid poisoning.
Does Drying Reduce the Danger
This is the central question for anyone considering Johnson grass as hay rather than pasture. The good news is that the curing and drying process does reduce cyanide risk substantially. Hydrogen cyanide is a volatile gas, and as cut forage wilts and dries in the field, much of the free cyanide dissipates into the air. Properly cured hay that has been dried to normal moisture levels (around 15 percent or less) poses far less prussic acid risk than fresh-cut or wilted Johnson grass.
That said, “far less risk” is not “no risk.” The key word is properly cured. Hay that was rained on during curing, baled too wet, or stored while still damp may retain more cyanide potential than expected. Moist conditions slow the volatilization of cyanide and can create pockets in the bale where dangerous concentrations linger. Round bales with a damp core are a particular concern. Additionally, if Johnson grass was cut under severe drought stress or immediately after a frost, the starting cyanide levels may be so high that even normal drying doesn’t eliminate the risk entirely.
The practical takeaway: if you plan to make Johnson grass hay, cut it under normal growing conditions (not during drought, not after frost, not after herbicide application), tedder or rake it for good air exposure, let it dry thoroughly, and test bales if you have any doubt. Many county extension offices can arrange a prussic acid test, and the small cost of testing is negligible compared to the value of even a single cow.
Which Livestock Are Most at Risk
Cattle are the animals most commonly affected by Johnson grass cyanide poisoning, partly because they are the animals most commonly grazed on it. But ruminants in general, including sheep and goats, are vulnerable because their rumen bacteria are efficient at liberating cyanide from the glycoside compounds. Horses face a different but equally serious set of risks from sorghum-family grasses.
Horses that graze pastures dominated by sorghum species have been documented to develop cystitis (bladder inflammation) and ataxia (loss of coordination), a condition sometimes called sorghum cystitis-ataxia syndrome.3Australian Veterinary Journal. Equine cystitis and ataxia associated with grazing of pastures dominated by sorghum species The neurological damage appears to result from chronic low-level cyanide exposure affecting the spinal cord and urinary tract nerves. The condition can be irreversible. For this reason, most equine nutritionists and extension specialists advise against feeding any sorghum-family forage, including Johnson grass hay, to horses. Even if the acute cyanide risk is reduced by drying, the chronic exposure concern remains, and the consequences for horses are severe enough that the risk simply isn’t justified when other hay options exist.
For cattle, the risk profile is different. A well-cured Johnson grass hay fed to mature beef cattle is generally considered safe by most extension services, provided the hay was made under proper conditions. Calves, thin or stressed animals, and cattle on a protein-deficient diet may be more susceptible. Animals that have been without feed and are then given Johnson grass hay tend to gorge on it, which concentrates the cyanide load in a short period and increases the chance of a toxic dose.
Ensiling as an Alternative to Hay
Some producers in the South have turned to ensiling Johnson grass rather than drying it for hay, and the research on this approach is encouraging. Johnson grass harvested at a young regrowth stage and properly ensiled can retain good nutritive value. Studies have confirmed that to get the best combination of forage quality and quantity, Johnson grass should be ensiled before it reaches the flower stage.1PubMed Central. The impact of maturity stages on yield, quality, and nutritive value of ensiled Johnsongrass [Sorghum halepense (L.) Pers]
One advantage of ensiling is that the fermentation process further degrades cyanogenic glycosides. The acidic environment and microbial activity in the silo break down these compounds over time, and the resulting silage typically contains much lower cyanide levels than the original fresh forage. Adding microbial inoculants and enzymes to Johnson grass silage has been shown to improve fermentation quality, producing lower pH levels, higher populations of beneficial lactic acid bacteria, and greater lactic acid content compared to untreated silage.4Semantic Scholar. Fermentation characteristics of Johnson grass ensiled at two regrowth periods with silage additives Better fermentation means a more stable, palatable product and a lower risk of spoilage or clostridial contamination.
Silage isn’t a practical option for everyone, of course. It requires either a silo, a bunker, or equipment for wrapping bales in plastic, plus the ability to feed it out quickly enough once opened to prevent spoilage. For operations that already have that infrastructure, Johnson grass silage can be a legitimate low-cost feed. For a small producer with a few head of cattle and no silage equipment, hay remains the more realistic route.
Legal Status and the Weed Dimension
Any discussion of Johnson grass as forage has to acknowledge the elephant in the field: in many states, this plant is legally classified as a noxious weed, and deliberately cultivating it can create regulatory and neighborly problems. Texas passed legislation as early as 1895 making it illegal to plant Johnson grass on rented land. Six years later, the state began fining railroad companies that failed to control it along rights-of-way.2MSU Extension. Johnsongrass (P3205) Many other states across the midsouth and beyond have their own noxious-weed designations for Johnson grass.
This legal reality means that buying Johnson grass seed to establish a forage stand is usually a bad idea, even in states where it isn’t explicitly prohibited. The grass will escape your field. It will invade your neighbors’ crop rows. It will show up in soybean and cotton fields where it competes fiercely and is expensive to control with herbicides, especially now that glyphosate-resistant Johnson grass populations are spreading. What makes it attractive as forage (aggressive growth, deep rhizomes, drought tolerance) is precisely what makes it a nightmare as a weed.
The more defensible approach is to manage Johnson grass that already exists on your land. If you have a field or pasture margin dominated by Johnson grass, cutting it for hay before it produces seed heads serves double duty: you get forage value and you prevent seed set, slowing the weed’s spread. This is “making the best of a bad situation” agriculture, and it’s the context in which most Johnson grass hay is actually produced.
Hay Quality Compared to Purpose-Grown Forages
Putting the poison issue aside for a moment, how does Johnson grass hay compare in straightforward feed value to the forages most livestock producers grow intentionally? When cut at the boot stage, Johnson grass hay typically falls in the neighborhood of a medium-quality warm-season grass hay. Crude protein will often land somewhere between 8 and 12 percent, depending on soil fertility, nitrogen availability, and the exact growth stage at cutting. That puts it roughly in line with a decent bermudagrass cutting, though bermudagrass is more consistent and predictable because it’s bred for forage production and doesn’t carry the cyanide baggage.
Fiber levels in boot-stage Johnson grass are moderate but climb steeply once the seed head emerges. Late-cut Johnson grass hay can test above 70 percent neutral detergent fiber, which translates to poor digestibility and low intake. Animals eating it will fill their rumen with material they can barely extract energy from, and they may lose condition even while appearing to eat plenty. This is one reason Johnson grass hay has a bad reputation in some areas: producers who cut it late because they didn’t get to it in time end up with poor-quality hay, and word spreads that “Johnson grass makes lousy feed.”
The lesson is that timing is everything. A producer who manages Johnson grass like a deliberate hay crop, cutting on a schedule, fertilizing appropriately, and curing carefully, can make respectable hay. A producer who cuts a wild stand when they get around to it and bales whatever they find will likely produce something barely worth feeding.
Nitrate Accumulation, the Other Toxicity Risk
Prussic acid gets most of the attention, but Johnson grass can also accumulate dangerous levels of nitrates under certain conditions. When the plant takes up more nitrogen from the soil than it can convert into protein (typically during drought stress, overcast periods, or after heavy nitrogen fertilization), nitrate accumulates in the lower stems. Unlike cyanide, nitrate does not volatilize and escape during hay curing. This means Johnson grass hay can retain high nitrate levels even after thorough drying.
Nitrate poisoning works differently from cyanide poisoning. In the rumen, bacteria convert nitrate to nitrite, which enters the bloodstream and converts hemoglobin into methemoglobin. Methemoglobin cannot carry oxygen, so the animal essentially suffocates at the cellular level even though it’s breathing normally. Symptoms include chocolate-brown blood (as opposed to the cherry-red blood of cyanide poisoning), weakness, rapid breathing, and death in severe cases.
If you’ve cut Johnson grass during or shortly after a drought, or from a field that received heavy nitrogen applications, nitrate testing is just as important as prussic acid testing. Many forage-testing labs offer a nitrate panel alongside their standard nutritional analysis. Hay with moderate nitrate levels can sometimes be fed safely by blending it with low-nitrate forage to dilute the total intake, but hay with very high nitrate levels should be discarded or composted rather than risked on livestock.
Selling Johnson Grass Hay
If you produce Johnson grass hay and try to sell it, you’ll quickly discover that it has a reputation problem. Many buyers, especially horse owners, won’t touch it at any price. Cattle producers may buy it, but often at a significant discount compared to bermudagrass or bahiagrass hay of equivalent protein content. The discount reflects the real liability: if a buyer’s animal gets sick from your hay, the relationship (and possibly more) is damaged permanently.
Some sellers don’t label Johnson grass hay as such, mixing it with other grasses in a mixed-species bale and selling it as “grass hay.” This is ethically dubious and, in areas with strong noxious-weed laws, potentially a legal problem. Buyers with experience can usually identify Johnson grass by its thick, waxy stems and distinctive seed heads if any slipped into the bale, and being caught passing it off unlabeled damages your reputation in a market that runs on trust.
The most honest and effective use of Johnson grass hay is typically on-farm feeding to your own cattle. You control the cutting schedule, you know the curing conditions, you can test the bales, and you aren’t asking someone else to trust your management. For operations where Johnson grass is already a presence and commercial hay production isn’t the goal, converting a nuisance plant into winter feed that offsets purchased hay costs is a reasonable strategy. Just don’t confuse “reasonable strategy for managing an existing weed” with “good hay crop worth planting on purpose.” Those are very different conclusions.