Phenology - Nature's Planting Signs

This time of year I am weary of winter, so I'm excited to see daffodils and dandelions beneath melting snow. Observers of nature have been tracking signs of spring for thousands of years, recording notes on what is now called phenology – the study of seasonal change as reflected in plant and animal life. One of the first modern phenologists, Englishman Robert Marsham, began recording signs from nature in 1736, and kept it up for 62 years.

Historically, farmers and gardeners used phenology to help determine planting times. For example, dandelions in full bloom are often considered a sign that it's time to plant potatoes, with pea planting linked to full flowering of forsythia. While interesting, it is also true that nature's signs can vary wildly from one year to the next, as well as from one climate to another. I have lived where forsythias hardly ever got damaged by late freezes, but where I live now late freezes nip the blossoms almost every year. In truth, average frost dates are simply more trustworthy than forsythias. Likewise, lilacs are better used as indicators than as guides.

Phenology and Garden Insects

Insects have inhabited earth for millions of years, in the process developing refined schedules for emerging from dormancy and reproducing as quickly and safely as possible. So, it should come as a small surprise that phenology is becoming a useful tool for managing garden pests. For example, in some climates, early blooming of the invasive weed called Canada thistle coincides with peak activity by apple maggot moths. In areas of the US where wild chicory blooms on summer roadsides, the pretty blue flowers signal that it's open season for squash vine borers, which probably kill more unprotected squash and pumpkins than any other pest.

Keeping notes on such matters can yield excellent information. For example, when tracking populations of cabbage root maggots on Long Island, NY, observers found that the first emergence came in late April through May when wild yellow rocket bloomed. Daylilies blooming in late June and July signaled the second brood, with a large and nasty third generation accompanying the goldenrod days of August.

Accumulating notes on insect indicator plants over several seasons paves the way toward being a much more effective manager of pests that plague your garden year after year. This can help eliminate time wasted looking for pests that have yet to become active, and remind you to check plants closely when they are scheduled to be a certain insect's next main course. When my vanilla-scented valerian blooms, I start looking for Colorado potato beetles.

Phenology and Climate Change

Around the world, phenology has recently gone from a fringe science to a major information source for understanding the complicated subject of climate change. Phenology reporting programs involve tens of thousands of gardeners, bird watchers and other amateur naturalists, which together yield a huge amount of data. In the UK, the Nature's Calendar project needs more observers to keep up this important work.

In the US, citizens are encouraged to participate in the Nature's Notebook reporting program conducted by the National Phenology Network. At the University of Berlin, the International Phenological Gardens bring together observations from 89 gardens in 19 European countries. New programs in Australia and other countries will help to establish a bigger and better worldwide database, which often involves comparing current-day reports with hand-written journals kept by gardeners hundreds of years ago.

Scientists can measure climate change in terms of temperature, moisture, and changing sea levels, but only phenology takes matters to the next level to identify the breaking of long-standing natural links between plants, animals and even fungi. Fact: In much of the Northern Hemisphere, spring is arriving about a week earlier compared to prior centuries. This phenomenon is called "season creep," a phrase coined in 2006 to describe the slow expansion of the spring season.

While an early spring is good news to eager, adaptable gardeners, a one-week change can have huge repercussions for birds and other wildlife. For example, when migrating shore birds depend on the horseshoe crab eggs for food, and the crabs start running a week ahead of the birds, the likely result is underfed birds that raise fewer young.

We do what we can, growing gardens and working to make the world a more beautiful and productive place. As we wait on spring, we are wise to keep our eyes open and pencils handy to better understand the phenology of our one-of-a-kind gardens. Consider the Chinese proverb: "Spring is sooner recognized by plants than by men."

By Barbara Pleasant