MONTGOMERY, Ala. (AP) — David Francko has urged people for years to try to grow plants in seemingly unnatural climates, and now he has co-developed what he calls “the holy grail of horticulture” — a spray that could increase a plant’s tolerance to cold by as much as 10 degrees.

Francko, a biology professor and dean of the University of Alabama Graduate School, said the spray can be used to lengthen the growing season into the fall, protect plants from a late spring freeze and is intended for use by both commercial growers and backyard gardeners. He hopes it will be commercially available by the end of the year.

“Cold is the thing that causes the most economic damage, not just for farmers and growers but also for the home landscape,” he said.

To demonstrate the effectiveness of the spray, tentatively called FreezePruf, Francko used the peace lily, a tropical plant, as an example. He said that plant usually dies if the temperature drops to 30 degrees. When treated with FreezePruf, the lily doesn’t start showing damage until 25 degrees and some tissue is still alive at 20 degrees.

The spray also has been used to keep dwarf palmetto and needle and windmill palm trees alive for several years on the campus of Miami University in Ohio. He said the average winter low there is zero degrees, while those palm varieties tend to live in areas where the average winter low is 10 to 20 degrees.

Francko appeared on Martha Stewart’s television show in 2003 following the publication of his book “Palms Won’t Grow Here and Other Myths,” which offers advice to gardeners who want to grow plants outside of their traditional climates.

Charles Hall, a professor of agricultural economics at Texas A&M University, said he wasn’t familiar with Francko’s product. But he said it could have been helpful in April last year when a late freeze damaged fruit trees and other crops across the country’s agricultural regions, causing millions of dollars in damage.

“If growers can apply this spray and protect against late freezes, I think it’s something they would be very interested in,” Hall said. “It definitely has potential if it does what he says it does.”

Francko says the spray, which only has to be applied once or twice a year and can be used on short notice, enhances a plant’s natural cold protection mechanism. When the temperature drops, ice crystals form within a plant, destroying its cells, but the plant’s built-in system combats this, and the spray asists.

Francko said that in field and laboratory tests, FreezePruf lowered the temperature at which cold damage would normally kill a plant, helping hardier types survive below zero. The range of protection the spray offers is 2.5 degrees to 10 degrees lower than a plant would have been able to stand without it, Francko said.

Francko said the spray can’t protect mature fruits because they are too big and too full of water, but it is meant to protect leaves and flowers from plummeting temperatures, such as in a late spring freeze.

In addition, Francko said the spray could help people grow plants that are native to areas that are 100 to 200 miles south of where they live.

Francko came to the University of Alabama from Miami University in 2006. FreezePruf grew out of a research project he was involved in at the Ohio school. The spray’s co-developers are Kenneth Wilson, Quinn Li and Alejandra Equiza, all of Miami University.

Marc Teffeau, director of research and regulatory affairs for the American Nursery and Landscape Association, said he hadn’t heard of Francko’s spray but that it reminded him of a product called Wilt-Pruf that has been on the market for years. Teffeau said Wilt-Pruf is an anti-transpirant that keeps the plant from losing water, which can lead to the formation of ice crystals and damage a plant in the winter.

Francko said an anti-transpirant is one of the ingredients in FreezePruf, but that anti-transpirants alone do not increase a plant’s cold tolerance.