Before being purchased at a floral shop, Valentine's Day roses have had a lengthy journey from another continent, which continues once in the vase.

The enormous demand for roses on Valentine's Day overwhelms indigenous florists. The winter weather means high costs of lighting and heating greenhouses, which are essential to growing plants, Robert Berghage, associate professor of horticulture, said.

"You can sell roses the rest of the year, but the numbers you need for Valentine's Day are so huge," he added.

Woodring's Floral Gardens, 145 S. Allen St., is no exception. They order more roses to meet demand near the holiday. "Four-hundred dozen is a good estimate," said Kim Paley, an employee who helps out during the busy seasons.

Berghage said most of the roses seen today are from Central or South America, where they might have been cut from a bush nearly a month ago.

They are grown on the sides of mountains where temperatures and sunlight remain relatively constant because of the equator, he added.

"As a result you end up with ... higher quality roses," Berghage said.

Kathleen Brown, a professor of postharvest physiology, said the flowers shipped from the mountains were cut while still in the bud stage to keep them from being smashed or broken on the trip. Since the flower has not opened yet, risks of damaging the rose are less and while in flight, the roses are kept cold.

Berghage said keeping the flower cold, called cryopreservation, slows down its metabolism. While not getting it too cold, which would freeze the tissue and kill the flower, it helps to prolong its life much like storing food in a refrigerator does, he said. This is why floral shops keep roses in coolers, he added.

"Instead of lasting three days, it might last three weeks," Berghage said. "Hibernation isn't a perfect analogy, but it isn't a bad one."

Once the roses have made it safely from the mountainside to a household vase, Brown said making sure they are hydrated is very important, and there are three things that can hinder water-flow: air bubbles, healing compounds in the plant, and microbes.

"Losing water is a big thing," she said. A rose normally receives water via a root system from the bush it's attached to, in a process is called transpiration, she added.

On the leaves of the plant, there are little holes called stomates. Water evaporates through these holes, creating negative pressure inside the rose. This allows more water to be sucked up from beneath, she said.

"[The rose] is not evolved to be a cut flower," Brown said. However, it can make due by using its stem to suck up the water, instead of using the roots.

Little microscopic tubes called xylem act as straws inside the stem, transporting the water upward.

However, Brown said, when a rose is cut, the xylem get exposed to air. Although efforts are made to curtail transpiration during the flight to the U.S. by keeping the roses in a humid environment, an air bubble, nevertheless, gets sucked up into the stem, she said.

"It lodges itself in the base," Brown said. This embolism hinders the travel of water and nutrients up the plant. "Cutting off the bottom inch will keep the bubbles out," she said.

Along with air blockages in the xylem, the second thing that can happen is once a rose is cut, the tiny straws produce compounds to try to heal themselves, Brown said.

"The stem isn't going to make new skin, but it will have wound healing reactions," she said.

The third thing that can affect the transit of water is the presence of bacteria and microbes, Brown said. The water in the vase is teeming with sugars and yeast leaking from the cut-end of the stem, "things bacteria like to grown on," she said.

Berghage also said the bacteria and microbes clog the xylem, starving the plant of water.

"The stem is kind of like a straw. Once you plug it up, it is finished," he said.

Brown also said the life span of a flower doesn't differ, whether on a South American mountain or in a vase in Central Pennsylvania. Either way death process of the flower cannot be escaped.

"The individual life of a flower is about one week," Berghage said, not taking into account cryopreservation.