Almost no other plant splits a room of hay producers the way this one does. Ask about johnsongrass on any forage forum and you get two answers that sound like they are describing different species. Here is one, from a Tennessee grower opening a thread on control:
Those are two very foul words here in the Southland. In my travels in the North and Mid-West I notice that that stuff is very non- discriminatory. It likes many of our states.
— Vol, HayTalk, "Johnson Grass"
And here is the reply, four posts later, in the same thread:
One man's trash....
Around here (North Texas) Johnson Grass is a common hay crop. In the right fields you can get 4 cuttings a year. Makes great cow hay.
However, I don't want it in my hay fields either.
— JDSafeman, HayTalk, "Johnson Grass"
Both of those growers are right, and the last line of the second quote is the whole subject in one sentence: johnsongrass can be a good hay crop and something you do not want in your hayfield, at the same time, on the same farm. This guide is for producers who already have johnsongrass in a field and need to decide what to do about it — bale it, kill it, or manage it — and who need to know how to feed it without hurting anything.
Short answer
Johnsongrass makes genuinely good cow hay and is genuinely hard to live with. Cut vegetative or at boot stage it runs roughly 10–14% crude protein and 55–60% TDN — better than a lot of what shares the field with it.
The two toxins behave in opposite ways. Prussic acid is volatile and leaves as the crop cures, so properly dried hay is the safe form. Nitrate is stable, stays in the bale, and can actually concentrate as moisture leaves. Curing fixes one problem and none of the other.
It dries slower than what it grows with. A coarse, rhizome-fed stem in a bermudagrass or fescue windrow is the last thing in the field to be ready, and it decides your baling moisture.
To remove it, wick it — don't spray it. Anything that kills johnsongrass kills your desirable grass too, so growers overwhelmingly report using a rope or wiper applicator to reach it above the canopy.
The split is regional, and both sides are describing their own field
The argument in those threads is not really about the plant. It is about what else you could be growing. Where the alternative is a well-managed bermudagrass or orchardgrass stand, johnsongrass is a thief that takes the field and lowers the sale price. Where the alternative is whatever volunteers on a river bottom, it is the best thing out there.
I want nothing to do with Johnson grass. Complete junk.
— Colby, HayTalk, "Johnson Grass"
My exact thoughts Colby. HERE, the only people that feed JG are those that are too lazy or cheap to fight it. Crabgrass is high in protein but I am not going to intentionally grow it.
— Vol, HayTalk, "Johnson Grass"
That crabgrass comparison is sharper than it looks, because it is exactly the same argument — and our crabgrass hay guide covers a plant that made the same journey from weed to deliberate crop in parts of the South. Meanwhile, in the other thread:
There are cattle farmers in my state who raise Johnson grass as their primary hay forage.
— Tim/South, HayTalk, "Johnson Grass"
Neither camp is wrong about their own ground. What decides it is whether the field has a better option and whether you intend to sell the hay off-farm.
It is here because somebody planted it on purpose
This is the piece most producers do not know, and one forum member laid it out plainly:
Johnsongrass was originally IMPORTED to the US and planted specifically as a high-value, high productivity animal forage. It is not native to the United States. You will find that MOST of our most valuable forages have a similar history.
— luke strawwalker, HayTalk, "Johnson Grass"
That is accurate. Sorghum halepense is native to the Mediterranean basin and North Africa, and it arrived in the United States in the early 1800s as a candidate forage. The common name traces to Colonel William Johnson, who planted it on river-bottom ground near Selma, Alabama in the 1840s — though the plant was already in several states before that, arriving both deliberately and as a contaminant in seed lots.
It worked. That was the problem. The same rhizomes and prolific seed set that made it productive made it permanent, and it is now a listed noxious weed in roughly two dozen states, with seed laws restricting its sale and movement. If you sell into markets that require a weed-free certification, that listing matters directly — see certified weed-free hay for how those inspections actually work.
There is a practical consequence in that history for how it keeps coming back:
It keeps coming back because the road district mows the banks and spreads the seed all over hell-and-creation.
— rjmoses, HayTalk, "Johnson Grass"
Roadside mowing is a genuine reinfestation route, and it is one reason total eradication on a small acreage is usually not a realistic goal. Control is.
What it actually tests
The nutritional case for johnsongrass is stronger than its reputation. North Carolina State University Extension puts vegetative johnsongrass at 10–14% crude protein and 55–60% TDN, and notes it is highly palatable in that state. Clemson University Extension lands in the same place: protein averaging about 12%, TDN around 55%.
A producer running it as a crop reported numbers on the conservative end of that range:
Johnson grass,cut in boot stage, will test at about 8 percent protein,(or better)and is highly palatable. It takes very little input to make a hay crop.Not for everyone,but not the boogie man many accuse it of being.
— tommystunes, HayTalk, "Johnson Grass"
Both can be true. Published extension figures are usually for vegetative material; boot stage is later, and quality in this species falls off a cliff as it matures. NC State is explicit that as johnsongrass matures the nutritive value drops quickly and animals stop grazing it. The window is early, and it is narrow. If you are going to make hay out of it, treat it like any other summer annual grass and cut on maturity, not on the calendar — the same discipline described in our guide to reading a hay test.
Palatability is not in dispute anywhere:
If johnsongrass is grazed or hayed at the proper time, it is literally "ice cream grass"... cows will eat it preferentially over ANY other grass in a field, if given a choice.
— luke strawwalker, HayTalk, "Johnson Grass"
That preference is also the single most useful control tool available, and we come back to it below.
Two toxins that behave in opposite ways
This is where johnsongrass earns its reputation, and where most of the bad advice lives. Johnsongrass is unusual in carrying both risks in the same plant: it is a cyanogenic sorghum and a nitrate accumulator. Our full guide to prussic acid and nitrates in baled forage works through the testing thresholds and the units traps in detail. What matters here is the difference between the two, which a Texas producer stated correctly and compactly:
Prussic acid can be caused from stress such as lack of rain then rain causing accelerated growth or frost. If JG has Prussic acid when baled the PA will dissipate after hay has been stored about 3 or 4 wks. On the other hand Nitrate poisoning never goes away
— Tx Jim, HayTalk, "Johnson Grass"
That matches published guidance. Prussic acid — hydrogen cyanide — is volatile, and NC State Extension states directly that if you are mowing johnsongrass for hay, the prussic acid should dissipate as it dries down. Extension sources commonly add a storage interval of several weeks before feeding hay cut from stressed or frosted stands.
Nitrate does not do any of that. It is stable. It stays in the bale indefinitely, and because it stays while water leaves, the concentration in the cured hay can be higher than in the standing crop. There is no waiting period that fixes it. The only tools are testing and dilution.
| Prussic acid (HCN) | Nitrate | |
|---|---|---|
| Triggered by | Frost, drought broken by rapid regrowth | Drought plus available nitrogen |
| Where the risk is highest | Young, lush regrowth; grazing and green-chop | Lower stem of drought-checked plants |
| Does curing remove it? | Yes — volatile, leaves with the moisture | No — stable, can concentrate |
| Wait before grazing | About 5 days (NC State); up to two weeks (Clemson) | Waiting does not help |
| What to do | Cure it fully; do not graze stressed regrowth | Test the lot. Then dilute or do not feed |
The two extension services differ slightly on the post-frost grazing interval — NC State says wait about five days, Clemson recommends up to two weeks after a drought or frost event. Take the longer number when you have the grazing available to take it. Neither interval has anything to do with nitrate.
A cattleman in the first thread framed the risk correctly without overstating it:
Johnson grass doesn't hurt much especially for cattle. If it's been stressed or highly fertilized though be careful of Prussic acid or nitrate poison.
— CBarM, HayTalk, "Johnson Grass"
"Stressed or highly fertilized" is the entire risk profile in four words. A johnsongrass field that got rain on schedule and no extra nitrogen is a low-risk feed. The same field after a dry August, or after a manure application, is a hay test waiting to be taken.
The traceability problem that turns a risk into a loss
One Georgia producer's account of a drought year contains the most transferable lesson in any of these threads, and it is not about chemistry:
Problem was we weren't sure which farm the rolls had come off of due to the fact we were baling and buying anything we could get our hands on.
— David in Georgia, HayTalk, "Johnson Grass"
Drought is precisely when nitrate risk peaks and when hay comes from everywhere at once. If you cannot say which field a bale came from, you cannot test a lot, and you cannot pull a suspect lot out of the feeding order. Mark the rows as they are stacked. In a short year that record is worth more than the test itself, because it is what makes the test actionable.
Baling it: the drying problem nobody warns you about
If there is one purely practical fact in this article that will change what you do next week, it is this one. Johnsongrass is a coarse, thick-stemmed plant fed by rhizomes, and it does not dry at the same rate as the fine-stemmed grasses it usually invades. Clemson Extension states it plainly: johnsongrass can be used to produce hay, but it may be challenging to dry. A Texas producer had already worked that out from the seat:
I dislike JG in a Coastal field just because JG dries slower than Coastal and horsey people don't like it.
— Tx Jim, HayTalk, "Johnson Grass"
The consequence is worse than "wait another day." In a mixed windrow, the wettest component sets your baling moisture, but the driest component sets your leaf loss. Wait for the johnsongrass stems and you overdry the bermudagrass or fescue around them. Bale on the fine grass and you put wet cores in the bale.
What actually works:
- Cut earlier than you would for the companion grass. A younger johnsongrass stem is thinner and cures closer to the rate of what surrounds it. This also lands you in the quality window instead of past it.
- Condition it properly. This is a stem-drying problem, which is exactly what a conditioner exists to solve. Our guide to making dry hay faster covers roll settings and swath width.
- Lay the widest swath the mower will make. Stem drying is driven by exposure, and a wide swath is the cheapest intervention available.
- Ted it if the field justifies it — a coarse stem tolerates mechanical handling far better than alfalfa leaf does, so the usual objection to tedding is weaker here. See the tedder guide.
- Test the bale, not the windrow. A stem that reads dry on the outside can still be carrying moisture in the middle, and heating in the stack is the result.
That last point matters more with johnsongrass than with fine grass. Thick stems are the classic cause of a bale that tests fine at baling and heats a week later. If you are baling a heavy, stemmy crop, the wrap has to hold a firm bale shape while that moisture equalises — our notes on how many wraps per bale and on storing round bales both apply directly.
Horses: the one place experience and extension disagree
On the forums, the horse question gets a confident answer:
Yes horses can eat & do well on Johnson grass in all stages except when it has Prussic acid or nitrate poisoning. Horse owners are the ones that think horses can't eat JG.
— Tx Jim, HayTalk, "Johnson Grass"
We are not going to paper over the disagreement here, because it is a safety question and the published guidance goes the other way. Clemson University Extension recommends against grazing johnsongrass with horses, citing the risk of equine cystitis — a bladder and neurological syndrome associated with grazing sorghum species that is a separate mechanism from acute cyanide poisoning and is not addressed by any of the usual prussic-acid precautions.
Two honest observations about how those positions fit together:
- The extension caution is specifically about grazing sorghum species — horses standing on a stand and eating fresh growth over weeks. That is a different exposure from a percentage of johnsongrass in cured hay.
- Producers reporting good results are describing cured hay, often as a component of a mixed bale rather than a straight johnsongrass diet.
For a commercial hay seller the practical conclusion does not depend on resolving the science, because the market has already decided. Tx Jim's own sentence contains it: horsey people don't like it. Johnsongrass in a horse-hay bale is a discount and an argument even when the horse is fine. Sell it as cow hay. Our guide to hay and net wrap for horse owners covers what that buyer is actually inspecting for.
If you want it gone
The control problem is structural. Johnsongrass spreads by seed and by rhizome, so a pre-emergent herbicide can work on the seedbank while doing nothing at all to the established plants. And as NC State Extension notes, any chemical treatment that will kill johnsongrass will generally kill your desirable forage as well.
That constraint produces the strongest consensus in the entire corpus. Growers do not spray johnsongrass in a hayfield — they wipe it.
So to answer your question, Roundup in a wick applicator will give very good results.
My first application gave a 90 percent kill. Now I just spot treat the rest as it shows its ugly little head.
— JDSafeman, HayTalk, "Johnson Grass"
I spray Maverick (Monsanto) if there is a lot. It's a bit pricy but it works. Otherwise I just use a wick wiper with Roundup.
— Mike120, HayTalk, "Johnson Grass"
The mechanism is simply height. Johnsongrass grows to six or seven feet and stands well above bermudagrass, fescue or orchardgrass, so a wiper set above the canopy touches only the target. NC State Extension recommends wick application of glyphosate in the fall, when the plant is moving carbohydrate down into the rhizomes and carries the herbicide with it. That timing detail is the difference between top-killing it and killing the rhizome.
Selective chemistry exists where the base grass tolerates it. One grower flagged the option in a single line:
If you use Pastora it will leave your Orchard grass.
— Vol, HayTalk, "Johnson Grass"
Clemson Extension lists Pastora, Prowl H2O and Outrider among the products used against johnsongrass, and stresses that the choice has to account for which perennial grass dominates the hayfield. Tolerance is species-specific and label-specific: confirm your grass is on the label before you spend anything. Product names, rates and haying and grazing restrictions all change, and the label in force always governs — our weed control in hay fields guide covers how to read those restrictions.
The control method that costs nothing
The most reliable non-chemical tool is the plant's own palatability. NC State Extension notes that johnsongrass is highly susceptible to overgrazing, which is why it is rarely seen in pastures. Clemson says the same thing from the other direction — it does not tolerate continuous stocking and rapidly plays out. Cattle will find it and keep finding it until the rhizomes exhaust themselves.
Mowing works on the same principle and is slower. NC State recommends keeping it below six to eight inches to deplete rhizome carbohydrate reserves over time, while being explicit that mowing alone will not eliminate it. Note the tension with grazing management: Clemson's grazing recommendation is to turn in at 15–18 inches of canopy and leave a 6–8 inch stubble, which is how you keep a stand productive. Mowing to 6–8 inches repeatedly is how you wear one out. Same numbers, opposite intent — pick which one you are doing.
If you are keeping it
Some producers deliberately farm it, and the management is straightforward once you accept what the plant is:
- Cut early, cut often. Quality collapses with maturity. Vegetative to boot stage is the target; a headed-out stand is bedding.
- Go easy on nitrogen. Heavy N plus a dry spell is the recipe for nitrate accumulation, and this plant needs little help growing. Our fertilizing hay fields guide covers rate-setting from a soil test.
- Do not graze it hard if you want to keep it. The trait that makes it easy to kill makes it easy to lose by accident.
- Test in any year with a drought in it. Free or low-cost nitrate screening is available through many state labs.
- Expect the boundary problem. Rhizomes do not respect your fence line, and neither do your neighbor's. Keeping it in one field is work.
Selling hay that has johnsongrass in it
Three rules keep this simple and keep you out of trouble.
Disclose it. Buyers who want cow hay generally do not care and some actively want it. Buyers who find it after delivery do care, and that is a returned load and a lost account. Our guide to selling hay covers how to describe a mixed bale accurately.
Price it as cow hay. The first thread contains an instructive exchange in which a broker offered a low per-bale price while insisting the hay was no good for resale and was only for her own animals. Another member's read was blunt — that this was a sales pitch, and that the same hay would reappear as "mixed grass hay" once supply tightened. Know what you have before you take the first offer. Our how to price hay worksheet is built for exactly that conversation.
Check the certification question before you commit to a buyer. Johnsongrass appears on noxious weed lists in many states, so hay destined for public land, interstate movement or any weed-free program needs to be sourced from an inspected field.
The bottom line
Johnsongrass is not the boogie man and it is not a free hay crop. It is a productive, palatable, well-adapted forage carrying two toxins that behave in opposite ways, growing where you did not plant it, drying slower than what it grows with, and depressing the price of anything you sell into the horse market.
If you have good ground and a good stand, wick it out in the fall and keep spot-treating. If you have a river bottom and cows, cut it early, keep the nitrogen modest, test it in a dry year, and feed it with confidence. The one thing not to do is treat cured johnsongrass hay as automatically dangerous, or automatically safe. Which it is depends on the weather the field had, and a hay test is the only thing that knows.
Frequently asked questions
Is johnsongrass hay safe for cattle?
Yes, in most cases. Cured johnsongrass hay is widely fed as cow hay and tests around 10–14% crude protein and 55–60% TDN when cut vegetative. The exception is hay from a stand that was drought-stressed or heavily fertilized, which can carry nitrate that curing does not remove. Test any hay baled in a dry year before feeding it.
Does prussic acid go away in johnsongrass hay?
Yes. Prussic acid is volatile and dissipates as the crop cures and dries down, which is why hay is the safer form compared with grazing or green-chop. Extension guidance commonly adds a storage interval of several weeks before feeding hay cut from frosted or drought-stressed stands. Nitrate, by contrast, never dissipates.
How long after a frost is johnsongrass safe to graze?
North Carolina State University Extension advises waiting about five days after a frost before grazing. Clemson University Extension recommends up to two weeks following a frost or prolonged drought. Take the longer interval where you can, and avoid grazing young regrowth, which is the most toxic material in the stand.
Can horses eat johnsongrass hay?
This is genuinely contested. Many producers report feeding it without problems, but Clemson University Extension recommends against grazing johnsongrass with horses because of the risk of equine cystitis, a syndrome linked to sorghum species. Commercially it is also a discount, because horse buyers generally do not want it. Sell it as cow hay.
What is the best way to kill johnsongrass in a hay field?
A wick or rope wiper carrying glyphosate, applied in the fall. Johnsongrass grows well above most hay grasses, so a wiper set above the canopy hits only the target while a broadcast spray would kill the whole stand. Producers commonly report about 90% control on the first pass, then spot treatment afterwards.
Why does johnsongrass make hay hard to dry?
It is a coarse, thick-stemmed plant, and Clemson University Extension notes it may be challenging to dry. In a mixed windrow the johnsongrass stems are the last thing ready, so you either overdry the fine grass around them or bale wet stems. Cut earlier, condition it, and lay the widest swath the mower will make.
Is johnsongrass a noxious weed?
In much of the United States, yes. It is a listed noxious or quarantined weed in roughly two dozen states, and seed laws restrict its sale and movement. That matters if you sell into weed-free hay programs, move hay across state lines, or supply public land, all of which may require certified inspection.
How much protein does johnsongrass have?
Vegetative johnsongrass runs roughly 10–14% crude protein with 55–60% TDN according to NC State Extension, and about 12% protein with 55% TDN according to Clemson. Quality falls quickly as the plant matures, so a headed-out stand will test far below those figures.
Related guides
- Prussic acid and nitrates in baled forage — testing thresholds, units traps, and what actually reduces nitrate
- Sorghum-sudangrass baleage — the same chemistry in a planted crop
- Weed control in hay fields — herbicide selection and haying restrictions
- Poisonous plants in hay — what else to walk the field for
- Certified weed-free hay — inspection, listed species, and the markets that require it
- How to price hay — pricing a mixed or cow-quality bale honestly
Hero image: johnsongrass (Sorghum halepense) in seed head. Photo via Wikimedia Commons, used under its stated license.
