Quick answer: The last cutting is a go/no-go decision, not just a timing one. On alfalfa, the modern rule is not a calendar date — University of Wisconsin–Madison Extension frames it as growing degree days: harvest when more than 500 GDD (base 41°F) remain before a killing frost of 24°F so the plant can rebuild root reserves, or when fewer than 200 GDD remain so it will not try. The 200–500 GDD gap is the danger zone, and in Wisconsin that gap lands squarely on mid-September to mid-October. But two non-agronomic reasons kill more last cuttings than winterkill does: in the North you often cannot get it dry in October, and the tonnage is small — Wisconsin data puts a fourth cutting at about 0.77 tons DM/acre and a fifth at about 0.58, which can cost more to harvest than it is worth. Leave at least 6 inches of stubble whatever you decide.
Every fall the same argument runs on every hay forum. There is a crop standing out there. It is late. Somebody says the calendar rule, somebody else says they have cut in November for thirty years and never lost a stand, and both of them are telling the truth.
The reason both can be right is that the question has three separate parts, and most advice only answers one. Will cutting hurt the stand? Can I actually make dry hay this late? And is the tonnage worth the diesel? We covered the stand-survival window in when to cut alfalfa. This guide is about the other two, and about how to make the whole call.
The rule everyone quotes — and the number that breaks it
The familiar guidance is to leave four to six weeks of regrowth before your average first killing frost. It is sound. The problem is the input.
An Illinois producer trying to apply it hit the wall immediately:
"I am getting ready to do my last alfalfa cutting and was checking the first freeze date for the St Louis area - it ranged from 10/5 to 10/29."
— rjmoses · HayTalk thread 13852
He kept looking and it got worse:
"The thing I am most confused about is the first freeze date published on the Internet."
— rjmoses · HayTalk thread 13852
A three-and-a-half-week spread in the input makes a four-to-six-week rule useless. And "killing frost" is itself ambiguous — producers use different thresholds:
"If I remember it has to get down to 27 degrees F. for a minimum of three hours for it to be considered a killing frost for alfalfa."
— mlappin · HayTalk thread 13852
"Cold air of 22° for one ( 1 ) hour is a hard freeze."
— hay wilson in TX · HayTalk thread 15302
Extension guidance generally sets the reference point for alfalfa at 24°F sustained for several hours. If you are going to use a frost-date rule, at least fix the definition first, and use a local probability figure at a stated temperature rather than a generic "average first frost" date.
One thing this is not: a rule about seeding. As we note in establishing an alfalfa stand, there is no national "six to eight weeks before frost" seeding deadline — late-summer seeding windows and fall cutting windows are different decisions that happen to sit in the same weeks.
The better version: count growing degree days, not weeks
The calendar rule is a proxy. The thing it is standing in for is how much regrowth the plant can achieve before it shuts down — and that is measured in heat, not days.
University of Wisconsin–Madison Extension states it directly: research in the northern US and Canada indicates alfalfa requires 500 growing degree days (base 41°F) between the final harvest and a killing frost of 24°F for enough regrowth to support winter survival and full yield the following spring. So the recommendation becomes a two-window rule:
- More than 500 GDD remaining — safe to cut. The plant has time to regrow and refill the taproot.
- Fewer than 200 GDD remaining — also safe. Regrowth will be insignificant, so the reserves already banked stay banked.
- Between 200 and 500 GDD — the danger zone. Enough warmth to trigger regrowth, not enough to pay it back.
This is why the old-timers who cut late and never had a problem are not wrong: they are landing in the under-200 window on the far side of the danger zone, not sneaking through it.
Wisconsin also did the historical work. Using 42 years of weather data, retired UW forage specialist Dan Undersander found the highest-risk period in southern Wisconsin is mid-September through mid-October; in the north it is the last half of September. Their conclusion is worth reading twice: delaying fall harvest until mid-October is often safer for all areas of the state, regardless of the occurrence of frost.
Producers arrived at the same shape of answer from experience. A Texas grower uses day length as his trigger, which is a decent field proxy for the same physiology:
"I do not like to cut hay after 8 October, as that is when we have 12 hours of day light including twilight. When the nights become longer than 12 hours of darkness that is when the plant is putting a higher percentage of energy into growing roots."
— hay wilson in TX · HayTalk thread 13847
And an Indiana producer's numbers are exactly the four-to-six-week rule, stated with the local inputs filled in:
"Suggested last date to cut alfalfa in our county is September 15th. Historic frost date is October 15th."
— mlappin · HayTalk thread 13847
An Oklahoma producer had read the physiology and asked the right follow-up question — how would you even know?
"I live in NE Oklahoma and read that last cutting should not be taken from Mid September to Mid October because plant is preparing for winter and translocating sugars/carbs to root system."
— OKrookie · HayTalk thread 15302
Risk 1: you may not be able to get it dry
This is the reason a last cutting most often goes wrong in the North, and it has nothing to do with root reserves. Shorter days, lower sun angle, heavy dew, and humidity that never drops mean the windrow simply will not cure.
"I have made hay a few days after a killing frost as well, but for the most part this far north, by time you get to teh latter part of September and into October, you're just kidding yourself if you think you can cut and get it dry in any reasonable amount of time."
— mlappin · HayTalk thread 13847
The clearest illustration is a North Dakota producer's account of what a late cutting actually cost him. He cut and tried to bale 130 acres:
"The day I was going to bale, the hay would only reach 22% moisture. Just couldn't get the stems dry."
— NDVA HAYMAN · HayTalk thread 13852
Then it rained seven inches. The result:
"when it was all said and done, I baled 9- 5x6 bales leaving 50 acres in the field that was not worth raking."
— NDVA HAYMAN · HayTalk thread 13852
"I wish I had not cut it and left it for a good first cutting next year."
— NDVA HAYMAN · HayTalk thread 13852
Nine bales off 130 acres, plus the winterkill exposure he took on for nothing. That is the downside case, and it is not rare.
It can be done — but it takes deliberate commitment, not optimism:
"I plan to make dry into the beginning of November. Have now 2 years running. It takes a different mindset when we get late into Sept and I feel people just don't want the challenge."
— IH 1586 · HayTalk thread 101300
If you are going to try it, plan for a long cure and know your options for hay that will not reach baling moisture — see hay preservatives and baling moisture for net-wrapped bales. A late bale that goes up tight and damp is the one most likely to mold in storage.
Risk 2: the tonnage is smaller than it looks
A field with knee-high regrowth looks like a crop. It usually is not much of one.
The Wisconsin Alfalfa Yield and Persistence Project measured it: the fall cutting in a four-cut system yields roughly 0.77 tons of dry matter per acre, and the last cutting in a five-cut system roughly 0.58. Wisconsin's own conclusion is blunt — the cost of harvesting a final fall cutting may exceed the value of the forage.
Run your own numbers before the mower leaves the shed. Mowing, tedding, raking, baling, wrapping, and hauling half a ton of dry matter per acre is a thin proposition in any year, and thinner if the hay ends up rained on. Some producers reach the same conclusion for market reasons and simply stop:
"We brushhogged 30 acres instead of baling it due to reduced sales. That might be something to consider instead of giving your nutrients away then needing to buy more."
— IH 1586 · HayTalk thread 102790
That last clause is the part people miss. Every ton you haul off takes potassium and phosphorus with it — roughly 50 to 60 lb of K₂O per ton on alfalfa, as covered in fertilizing hay fields. A marginal cutting you cannot sell exports fertility you then buy back.
What actually moves your risk
The same calendar date is a different bet on different fields. Wisconsin Extension lists the modifiers, and they are worth checking field by field:
| Factor | Lower risk | Higher risk |
|---|---|---|
| Harvest interval | Longer intervals; reserves refilled between cuts | 30 days or less all season — reserves never fully rebuilt |
| Stand age | 18 to 36 months — best crown health | Older stands with wheel-traffic and disease damage; first-year stands |
| Potassium status | Optimal K improves winterhardiness | Chronically short K — often misread later as winterkill or age |
| Soil moisture and drainage | Well-drained, drier fields; better trafficability | Wet ground delays dormancy, invites crown damage and frost heaving |
| Variety | Good winter-survival and disease ratings | Older genetics not bred for intensive cutting |
An experienced Iowa producer's dissent belongs here too, because it is honest about how much of this is weather luck:
"I do believe that a late cutting can take away tonnage from next years first crop, but I still can't resist harvesting what's there for the taking."
— IAhaymakr · HayTalk thread 13852
And his observation about where his losses actually came from is a genuinely useful corrective:
"Now that we are constantly cutting and baling I really just ignore the calendar and cut where there is a crop to cut."
— IAhaymakr · HayTalk thread 13852
Wisconsin agrees on the mechanism he describes: the reserves matter most when a warm spell breaks dormancy early and a hard cold snap follows. Fall cutting does not cause that weather — it just leaves you with a smaller buffer when it happens.
Whatever you decide: leave six inches
Stubble height is the cheapest risk reduction available, and it is the step most often skipped when people are racing weather.
Wisconsin Extension recommends leaving at least six inches of stubble on a fall cutting. It insulates the crown, catches and holds snow, and — the part most producers have not heard — taller residue interferes with ice-sheet formation, improving air exchange and reducing suffocation during icing events.
Producers running warm-season grasses arrive at the same number for a different reason:
"Plus I like to have a 6 to 8 inches of grass with the first killing frost. This shades the soil and discourages weeds from germinating."
— hay wilson in TX · HayTalk thread 13847
A North Dakota producer uses regrowth height as his go/no-go signal:
"I like to see 8" of regrowth before the first hard frost."
— NDVA HAYMAN · HayTalk thread 13852
One caveat if you have a vole or gopher history: tall matted residue going into winter is also cover for them, so weigh insulation against rodent pressure on fields with a known problem.
Grass hay is a different decision
Nearly all the "critical fall period" advice is alfalfa advice. Grasses do not carry the same taproot-reserve risk, and the last-cutting question shifts to whether it is worth fertilizing for.
The nitrogen answer is conditional on rain, and getting it wrong wastes the money outright:
"You would be wasting your money, especially in a drought. You need rain for N otherwise you'll lose it to volatilization."
— Hayjosh · HayTalk thread 101300
There is also a drying penalty that ties straight back to Risk 1:
"We have increased the nitrogen some tears depending on rainfall, but too much N can make the hay hard to dry down for us."
— Beav · HayTalk thread 101300
Pushing nitrogen for a late cutting in the North therefore stacks two risks: you may not get the rain to make it work, and if you do, the heavier, greener crop is harder to cure in October.
In the South the calculus changes again, because the season simply runs longer:
"It takes a really hard frost to send the grass into dormancy but sometimes it takes 2-3 or more light frosts and cool days to send it into dormancy."
— Customfarming · HayTalk thread 13847
"Last year here in NE TX we were baling hay up to about 2 weeks before christmas."
— Customfarming · HayTalk thread 13847
And irrigation removes most of the uncertainty. A Texas panhandle grower cuts on a fixed late date every year with old stands to show for it:
"Our 5th or last cutting is around the 25th of october"
— panhandle9400 · HayTalk thread 15302
For bermudagrass specifics see the coastal bermuda hay guide; for cool-season grasses, the orchardgrass guide.
Four things to do instead of cutting it
- Leave it standing as insulation. The cheapest option and often the best on a stand you intend to keep. Six to eight inches of top growth catches snow and shades out winter weeds.
-
Graze it. A Texas forage specialist's suggestion for bermudagrass — apply about 60 lb N/acre and let it grow to frost as standing forage — moves harvest cost to the animals. See stockpiling forage for winter grazing.
"have you considered applying about 60 lbs of nitrogen per acre and letting the grass grow until first frost for standing hay to be grazed by your cattle?"
— vhaby · HayTalk thread 13847
- Clip or brush-hog it. If the growth is weedy or too short to bale, clipping cleans the field for a good first cutting next spring without the fuel and wear of a full harvest.
- Wait for the freeze and cut then. Once you are under roughly 200 GDD, cutting no longer triggers costly regrowth. Just be honest about whether you can cure it.
Whatever comes off the field, late-season bales usually sit longest and get fed last, so storage matters more on this cutting than on any other — see net-wrapped bale storage outside and outdoor storage through a Midwest winter. Bales made in cool, damp fall conditions carry more moisture into the stack, which is exactly when good wrap coverage and a dry base earn their keep.
A last-cutting checklist
- Fix your frost definition. Use 24°F for alfalfa, and a local probability figure — not a generic average first-frost date off the internet.
- Estimate GDD remaining. More than 500, cut. Fewer than 200, cut. In between, strongly consider leaving it.
- Check the forecast for a real drying window, not a hopeful one. Fall cures take longer than you remember.
- Price the cutting. Half to three-quarters of a ton of dry matter per acre against your full harvest cost.
- Grade the field. Stand age, cutting interval, potassium, drainage. A tired, intensively cut, wet field is the worst candidate.
- Set the cutterbar high. Six inches minimum.
- If in doubt, leave it. The stand is the asset; a half-ton of October hay is not.
Frequently asked questions
Should I take a last cutting of hay in the fall?
Only if it clears three tests: the stand can afford it, you have a genuine drying window, and the tonnage covers the harvest cost. Wisconsin data puts a fall cutting at roughly 0.58 to 0.77 tons of dry matter per acre, which can cost more to harvest than it is worth. When those tests are close, leaving the crop standing is usually the better bet.
What is the 500 growing degree day rule for alfalfa?
University of Wisconsin–Madison Extension notes alfalfa needs about 500 GDD (base 41°F) between the final harvest and a 24°F killing frost to regrow and rebuild root reserves. So cut when more than 500 GDD remain, or when fewer than 200 remain so regrowth is insignificant. Between 200 and 500 is the highest-risk window.
Can you cut alfalfa after a killing frost?
Yes, and it is one of the two safe options. Once growth has been shut down, cutting does not trigger regrowth that would drain root reserves. Producers in irrigated and southern regions routinely take a final cutting after frost. The practical limit is drying — curing hay in late fall is slow and often impossible in northern states.
How tall should I leave the last cutting?
At least six inches of stubble. Taller residue insulates the crown, catches and holds snow, and interferes with ice-sheet formation so the stand gets better air exchange during icing. Warm-season growers leave six to eight inches for the same insulation benefit plus weed suppression. The exception is fields with heavy vole pressure, where matted residue provides cover.
Should I fertilize for a late fall cutting?
Only with rain in the forecast. Surface-applied nitrogen is lost to volatilization without moisture to wash it in, so a drought application is wasted money. There is a second catch: heavier nitrogen produces a lusher crop that is harder to dry down, which is already the main obstacle to making late hay.
The XES Netting team manufactures bale net wrap for round balers and writes these guides so forage operators can find clear, source-cited answers. Every farmer quote in this post comes from a real HayTalk discussion, linked at the quote — go read the threads in full. Agronomic figures (the 500/200 GDD windows, the 24°F killing-frost reference, six-inch stubble, and fall-cutting yields) come from University of Wisconsin–Madison Extension; confirm the specifics for your variety, region, and field.
Featured photo: Alfalfa field — Yonca tarlası by Zeynel Cebeci, licensed under CC BY-SA 4.0, via Wikimedia Commons.
