Phenology deals with the relations between climate and recurring biological phenomena, such as bird migration or plant flowering. Put more simply, phenology is the study of when things happen in the natural world. It’s a science that involves the study of many activities of animals, insects, and plants, such as birth, budding, flowering, hibernation, leafing, mating, migration, nesting, and more.
Phenology has countless broad applications for agriculture, biology, environmental science, health care, and other areas of research. For example, it’s used in medicine to help predict and mitigate allergy season (Here are six home remedies for allergies that you probably didn’t know about); in agriculture to anticipate and address problems caused by insects and other pests; and in environmental resource management to predict the growth and movement of invasive species. At the hands-on level, phenology is especially helpful to gardeners for planning when to plant and handle other gardening chores.
Lore or Observation?
People have been using such phenomena or “indicators” since ancient times. Known as phenophases, they are a visible stage in a plant’s or animal’s life cycle. If you’ve ever gardened according to adages such as “plant corn when oak leaves are as big as squirrels’ ears,” you’ve been practicing phenology. Although it may seem like folklore, it’s based on people’s observations and records of natural phenomena over several centuries and around the world, which is how these adages developed. (Read more adages about weather and nature.)
Perhaps most famously, Henry David Thoreau observed nature while walking each day and then made meticulous notes of what he had seen. By doing so over many years, he created a key historic record of when leaves emerged, birds migrated, and flowers bloomed. His journals are an essential environmental tool used by scientists to this day. Over time, Thoreau and countless other observers developed descriptions of nature’s indicators that are now a part of books, “farmers’ wisdom,” folklore, and journals about farming and gardening, as well as birding, entomology, and more.
Nature’s timing is exquisite. By the time birds lay their eggs, for example, shrubs and trees have leafed out enough so there’s cover from predators. By the time fish return to their spawning waters, insect larvae have hatched so there’s a ready food supply. Using phenology—relying on nature’s indicators rather than a set date on a calendar—may be the best way to triumph in the garden because it’s watching, learning, and working with nature rather than using other guides that are less connected to nature.
Taking Cues from Nature
Effective phenology for gardening is ultimately a homegrown activity because it relies on local indicators to help you determine when to plant various crops, when to undertake different garden chores, and when to anticipate the arrival of insects and other pests. It makes sense because indicators in the Southwest won’t necessarily work in New England. Therefore, phenological information is not one size fits all.
You can get information for your area at regional botanical gardens, cooperative extension services, environmental organizations, garden clubs, nature conservancies, plant stores and nurseries, and universities with agriculture programs. Master gardeners and master naturalists are also great resources. Phenology is also open to some interpretation, which makes what you observe, track, and record about the natural phenomena right around you the very best way to get the most beneficial information for your garden.
Examples of using indicators or phenophases include planting when the spring peepers begin peeping; treating the lawn for crabgrass when the forsythia is blooming; and ending the hunt for morel mushrooms once the dogwoods stop blooming. Some plants are considered indicator plants, and certain ones seem to do a lot of the heavy lifting. Lilacs and maples, for example, provide a lot of information because they grow in so many parts of the US. In addition, lilacs were tracked in the 1950s as part of a US Department of Agriculture-sponsored phenology observation network. Here are just some of the lilac and maple indicators:
- When lilac leaves are the size of a mouse’s ear, sow peas, lettuce, and other cool-weather crops.
- Around the time purple lilac blooms, grasshopper eggs hatch (See if grasshoppers are good or bad for your garden.)
- When lilac is in full bloom, plant beans.
- Once lilac flowers have faded, sow squash and cucumbers.
- When maple leaves begin to unfold, plant perennials.
- When maple leaves reach full size, sow morning glories.
Changes in Climate Make Phenology More Important
If phenology deals with the relations between climate and recurring biological phenomena, then how does climate—and especially climate change—factor in? Climate refers to the average weather conditions, such as temperature and rainfall, of a place. Climate change is a significant shift in the average conditions over a long period of time, such as places becoming warmer or drier. The longer period of time is what sets climate change apart from variations in weather conditions. Global warming—the rise in the global average temperature—is one aspect of climate change, and there are many others including spring events occurring earlier and fall events happening later; rising sea levels; and ice melting at faster rates in Greenland, Antarctica, and the Arctic. Changes in flower and plant blooming times, that is, changes in phenophases, is yet another aspect.
Climate change has made phenology more valuable than ever before, because phenology is so sensitive to changes in the climate. (At times, phenology even responds to changes in the weather.) Climatologists and other scientists are studying phenology as a key way to track how the timing of phenological events is changing over longer time periods, as climate conditions change.
A leading initiative in this effort is the USA National Phenology Network (USA-NPN), a national-scale monitoring and research partnership of government agencies, nonprofits, educators, researchers, and citizen scientists. According to USA-NPN, changes in phenology are the fingerprints of climate change.
A key project of USA-NPN is Nature’s Notebook in which professional and citizen scientists record long-term observations of animal and plant life stages. This is a massive undertaking and volunteers are needed. As you observe what’s happening right around you and keep track of it in your own gardening log, you may also want to participate in Nature’s Notebook. By doing so, you’ll be helping your garden and the planet at the same time.
As it turns out, nature’s schedule is still reliable, but not according to set dates on the calendar or timing that has worked in the past. The seasonal patterns and weather conditions that could be relied on are shifting. Nature continues to provide cues, but as the climates changes, so do those cues. By being observant and aware of when biological events are occurring and then acting in accordance with them is the best way to achieve ultimate gardening success.
Do you already garden according phenology?
What are some signs in nature that you look for?
Let us know in the comments below!
Jean Grigsby is a writer, who lives on the banks of the Kennebec River in Chelsea, Maine. She enjoys working out, reading, and running her marketing and public relations business, The Write Approach. Her article, Where Are All The Birds? appears in the 2021 Farmers' Almanac.