You know what they say about April showers, right? Well, when all those May flowers start to poke their heads out to say hello, you may see some familiar faces in your back yard. Many plants live and die within one growing season, so gardeners must replant them each spring. But others have evolved to linger year after year, so they can blossom anew without any help from a human horticulturalist (that’s someone who studies the science of plants).
Many flowers are what we call annuals. Their entire life cycle — from seed to death — takes just one year. They might leave behind sleeping seeds that could sprout again in the future, but the flowers, roots, stems and leaves all fade away as soon as the season is done. Sunflowers and petunias are examples of annuals.
Some plants technically last a little longer, but not in a way humans can truly appreciate. Biennials [bi-EN-ee-
als] take two years to start flowering instead of shooting up in a single spring, but they still wither and die once the flowers are gone. One to look for is a foxglove, a tall plant with clusters of bell-shaped blooms, often in pink or purple.
Then there are perennials [per-EN-ee-als], which can survive for years. Scientists believe these types of plants came first.
According to James Boyer, the vice president for children’s education at the New York Botanical Garden, annuals may have evolved to survive in areas where water was scarce.
“Annuals are putting all of their chips into the reproduction basket,” Boyer explains. “All of the energy to make roots and shoots is just enough to create an overwhelming display of flowers. They are evolutionarily gambling that they will create enough seeds to continue the species.”
The perennial strategy is to be a jack-of-all-trades, tucking tissues inside protective buds or bulbs to keep cells fresh until it’s time to bloom again. Perennials devote a lot more of their fuel to keeping themselves alive than annuals do.
“Roots, stems and leaves are repaired and grown each year,” Boyer says. Many eventually produce flowers, but it can sometimes take years — and in most cases, they’ll save enough energy to flower again the following season. The colorful tulips you see in many yards are perennials.
There are exceptions to this: “Monocarpic” plants spend decades growing before throwing all their resources into a single, brilliant season of flowers. They make thousands or even millions of seeds in one go, and then they die.
Whether a plant is a perennial or an annual can depend on where you plant it. Plants sold in cold regions that are labeled annuals could be tropical perennials; in warm weather they’d live for years, but a single harsh winter will kill them.
Boyer says that researchers are trying to trick annuals into sticking around. To survive for many years, a plant must have instructions in its DNA, or genetic code, telling its cells to save resources instead of spending them all on flowers. Scientists think they might be able to tweak the DNA of annual plants to send that message.
“If we could change corn into a perennial, we wouldn’t need to replant every year, which disrupts the soil and their fragile ecosystem,” Boyer says. “It could change our agricultural system.”