Valentine's Day is arriving. I want to buy flowers for my sweetheart, but it seems like a lot of resources go into growing and delivering a bouquet that will wilt just a few days later. You've suggested looking for eco-certified bouquets, but would I be better off just buying silk flowers instead?
This is a tough one. Comprehensive data aren't available for either real flowers or silk ones, but there's slightly more information available for the real thing—so let's start there.
Imported flowers have come to dominate the U.S. market in the last 40 years, as entrepreneurs and scientists have found ways to make blooms survive intercontinental plane trips. In 1971, just 8 percent of the roses, carnations, and chrysanthemums sold in the U.S. were imported. (These three flowers account for the majority of cut-flower imports.) By 2003, that number had grown to 91 percent, with most of those flowers coming from Colombia and Ecuador.
This shift from local to imported flowers is a mix of good and bad news for the environment. The bad news first: South American growers rely heavily on chemical fertilizers and pesticides. According to a 2007 study by the International Labor Rights Fund (now the International Labor Rights Forum) and the U.S. Labor Education in the Americas Project, 20 percent of the chemicals sprayed on Colombian flowers are illegal in the U.S. or Europe. They have contaminated the soil and caused severe health problems (PDF) for many workers. There are certification programs (PDF) for responsible growers, but it's often difficult to determine how any individual bunch of roses was raised.
On the other hand, flowers grown in equatorial zones and shipped to your local market probably use less total energy than the locally grown equivalent, despite spending five hours on an airplane. February isn't prime flower-harvesting season in most of the U.S., and efficient growing conditions usually trump buyer-producer proximity.
Ecologists at the U.K.'s Cranfield University compared (PDF) the environmental impact—including production and transport—of roses imported to England from the Netherlands with those coming from Kenya. The Dutch blooms required energy to heat their greenhouses but made a much shorter flight, while the Kenyan roses had the benefit of natural warmth but a long journey. In the end, the Kenyan roses were responsible for 0.4 pounds of carbon dioxide per flower, compared with 6.4 pounds per Dutch-grown rose. When the group took into account all greenhouse gases—including methane and nitrous oxide instead of just CO2—and adjusted for the fact that airplane emissions are especially damaging because they are injected into the atmosphere at high altitudes, the Dutch flowers had six times greater impact on global warming as did the Kenyan roses.
Unfortunately, nobody has conducted a comparable, comprehensive life-cycle analysis of silk flowers. Even so, it's possible to describe some of your silk pseudo-buds' environmental costs.
Although manufacturing silk requires a little more human intervention than harvesting roses, the super-smooth textile is still largely an agricultural product. Silk worms, the source of all real silk, feed on mulberry leaves. (Manmade flowers can also be constructed from cellulose-based rayon or petroleum-derived polyester. But let's save those down-market alternatives for a less romantic holiday.) Silk cultivators wait for the worms to form cocoons, which they collect after steaming the critters to death. The raw silk from the cocoons is spooled, boiled again, dyed, and then woven into fabric.
Mulberry trees are susceptible to viral, bacterial, and fungal infections, so most producers use chemicals to protect their crop. (Pesticides and fertilizers aren't used as heavily as they are in most crop fields, however, because the worms themselves are sensitive to chemicals.) Manufacturers use detergents, which can contribute to algal blooms, to separate the raw silk from the gum binding the cocoon together. Additionally, the bleaches and dyes often include dioxins, heavy metals, and a zo compounds, some of which are toxic.
Most of the energy required for silk production is spent on the steaming and boiling stages—and at the factories where the silk is spooled, woven, and wrapped into a sort-of convincing flower likeness. Unfortunately, there hasn't been enough research on the topic to assign a hard number to this energy use or the associated carbon dioxide output.