GRAND JUNCTION — It’s nail-biting time in the peach orchards. A freeze warning has gone out for this weekend, and wind machines, smudge pots and propane heaters are at the ready. So is a new bud-saving aid: amino acids.
Colorado State University Western Colorado Research Center horticulturist David Sterle has figured out that when temperatures plummet, the naturally occurring compounds of amino acids seem to act as a sort of cozy sweater for the little nubbins of future fruits.
Another way to put it is that the substance gives the buds a little help dealing with stress.
A spray of a calcium fertilizer containing amino acids is the first new addition to the arsenal of direct freeze fighters in western Colorado’s peach orchards in a long time.
“Basically, what I’ve been testing out is dietary supplements,” Sterle explained about his discovery of the cold-protective benefits of amino acids.
He uses the term “cautiously optimistic” when describing his discovery.
Some growers who have tried the spray are more effusive about its potential.
“We’re pretty excited about it. This could have national, no, worldwide significance,” said Cunningham Orchards operation manager Kaleb Easter. He has a 400-gallon sprayer ready to load with a fertilizer containing amino acids if the thermometer plunges in the orchard near Palisade this weekend.
Building blocks of proteins may help stressed out fruit buds
Like any science-based story, this one is going to take some explaining to show how organic compounds that serve as fundamental building blocks of proteins in humans and plants appear to have a bit of a magical effect on stressed-out fruit buds.
Sterle has been studying ways to make fruit crops hardier since 2014, when he was working on his master’s in pomology, a subspecialty of horticulture that focuses on improving fruit and nut crops.
As part of his research, Sterle wanted to find an affordable aid for growers whose crops can be wiped out by freeze-related crop losses.
Peach farmers stand to lose $15,000 to $20,000 per acre with a killing frost. The overall peach industry in Colorado could lose $60 million to $100 million over the next decade due to too much freeze damage, he said. Saving just 15% of the buds can mean a profitable crop.
Sterle started by examining exactly how frigid temperatures affect buds. He knew that could lead him to a way to thwart that process. He didn’t know he would find an answer in a jug of commonly used fertilizer.
He poked around in the more than 3,000 compounds contained in each minuscule peach blossom as he hunted for clues to show exactly what happens microscopically when a blossom freezes.
Sterle measured substances that change the freezing point of water, including glycols, sugars, alcohols and urea compounds. Some of them jumped up and down before and after a freeze event. But the fluctuations weren’t enough to be significant.
He looked at calcium, which is commonly sprayed on trees to improve quality and extend shelf life of fruits. It wasn’t compelling.
Sterle’s aha moment came in 2023 when he discovered that one compound — amino acids — “went through the roof” when a bud is exposed to cold. It appeared that the amino acids were attempting to protect the buds.
The effect would be pretty easy to test. All Sterle had to do was wait for a frost event, get out in the orchards ahead of it, and spray some buds with an amino acids-containing fertilizer, metalosate calcium. The fertilizer is commonly used and inexpensive. The amino acids are added to it to help the fruit absorb the calcium.
Sterle had lab test results indicating the spray would be beneficial, but he needed to prove it would work in the field.
By the time a frost was forecast and Sterle could test his hypothesis outside the lab, he was also preparing to defend his doctoral dissertation — “Peach Floral Bud Cold Hardiness” — in the halls of academia in Fort Collins. Sterle had to present his research, race back to the Western Slope orchards, fill up a battery-powered backpack sprayer with metalosate calcium, and coat the blossoms on three test trees.
The trees he sprayed got through the 26-degree weather with double the number of surviving buds compared with nearby unsprayed trees.
Sterle did five more field tests and every time, 50% to 100% more buds survived than in the nearby unsprayed trees.
Some growers are all in, others are skeptical
Sterle still carries on part of his research in a dungeon-like basement at the Orchard Mesa research center where he shares space with winemaking equipment and an obstacle course of hoses and buckets.
Sterle sprays budding branches with different substances, including amino acids, before cutting them from trees. He paints the tips different colors to identify them and fans them out on an improvised mesh tray. He then pops them into temperature-controlled freezers and gradually drops the temperature to see exactly when — and if — the cold turns lethal on the differently treated buds.
Sterle then goes into surgeon mode. He slices into the buds to look at their reproductive parts. If what he calls the “ovary” of a bud is a bright green, it’s still alive. Those with brown, shriveled ovaries are dead.
During the fall and winter, Sterle does another phase of his study by placing dormant buds into a device invented at the research center — a differential thermal analysis module. It has screwed-together layers of metal plates with indentations where Sterle places itty-bitty foil packets, each containing 10 tiny buds. He plugs the frame into a computer so he can carefully calibrate the temperatures for each experiment.
His computer spits out graphs that show the precise temperature at which individual buds die. Using this method, he has also been able to track how the little buds go through sort of death throes and give off a little flash of heat before succumbing.
That phenomenon was interesting for Sterle, but he found the bud-produced heat can also skew the results of his indoor testing, making it a little less reliable than his outdoor results.
Armed with charts and graphs and photos, Sterle trotted out his fledgling research to the annual meeting of the Western Colorado Horticulture Society in 2023. It piqued the interest of growers.
Easter said what he heard at the meeting persuaded him to try out the amino acids spray at Cunningham’s, which is one of the largest orchard operations in the Palisade area.
He was ready in 2024 when the next potentially damaging frost was forecast.
Easter sprayed 3 acres of peach trees the day before the temperatures dropped into the 20s.
In 2025, he sprayed a third of Cunningham’s 100-plus acres.
“Our sprayed trees did much better than our untreated trees,” Easter said. “It was very compelling.”
He said he knows many other growers have now stocked up on metalosate calcium to prepare for freezes.
Others are holding off until they have more research results.
Gwen Cameron, the owner of Rancho Durazno orchards, said she was impressed by Sterle’s research, but the tight timing and the wind-factor worry her on her 40-acre organic operation. She said she is open-minded about trying it in the future.
Sterle recognizes that the fertilizer spray is a bit fidgety to work with. As far as he knows now, it is only protective if sprayed on the blossoms within 48 hours of a plunge in the thermometer. He is still working to determine how long the protection lasts.
“I have had great results 40 hours after spraying. And I have seen a bit of benefit five days later,” Sterle said.
Sterle’s ongoing research is still sorting out other factors. He is looking at how wind, humidity and the height of buds on the tree canopy might impact the effectiveness of the spray.
He is studying dosing levels, additions of other ingredients and ranges of temperatures.
Without the spray, he knows temperatures that drop to 24 degrees will usually kill off all or most of the buds. At 27 to 28 degrees, some of the developing fruits can survive.
Those temps have hit Grand and North Fork valley peach trees three times in the past decade. In 2020, peaches were nearly wiped out by a deep freeze. In 2024 and 2025 there were significant spotty losses due to freezes.
Smudge pots and heaters aren’t obsolete yet
Sterle is not telling growers to chuck their smudge pots and propane heaters and mothball the wind machines that help to dissipate frigid air in orchards. The amino acids-containing fertilizer spray is simply another tool at this point — one that can give a few more degrees of protection. It may not sound like much, but raising temperatures a few degrees can have a huge economic impact.
“Just five degrees in this industry might mean losing $35 million to $20 million of fruit,” Easter explained.
Boosting the temperature hardiness with the fertilizer spray costs only about $30 an acre.
Sterle will be out in the orchards this weekend carrying on his research. He plans to be spraying trees with an organic version of metalosate calcium in Dominguez Canyon and at the Rogers Mesa Research Center near Hotchkiss, where the lowest temperatures are forecast.
Research scientists don’t believe in crossing their fingers, but Sterle is doing a bit of that as he faces a long weekend of working through cold nights alongside scared but hopeful peach growers.
“I’m hesitant to declare victory,” he said. “But this just keeps working time after time.”