Forget the calendar; phenology will tell you when it’s spring

Plant corn when oak leaves are the size of a squirrel’s ear. Prune roses when forsythia blooms. Potatoes, beets and brassicas can be planted when dandelions flower.

These adages, or old wive’s tales, depending on your perspective, are all rooted in phenology, the study of seasonal changes in plants and animals, and they are generally accurate.

It makes sense that generalities can be drawn about plants, whose schedules are dictated by heat accumulation. This is a metric known as accumulated growing degree days, which, like many science-related phrases, has the effect of being a simple descriptor that sounds incredibly boring. And that’s a shame, because the information that comes from AGDD and other phenology-based data is a fascinating and helpful tool that helps us understand what’s happening in our part of the world.

A look at the website for the National Phenology Network, a monitoring and research initiative to collect and provide information on what’s happening in nature, starts with some good news for southeastern Wisconsin: spring, as measured by the conditions we recognize as springlike, not a date on the calendar, is a bit ahead of schedule. As of this week, Ozaukee County had accumulated between four and six more growing degree days than the 30-year average.

Growing degree days also dictate when insects hatch, so phenology can help track when insect populations will be at their peak. The phenology network has data for that too, forecasting when emerald ash borers and Japanese beetles, to name two common pests, will hatch and emerge as adults. This makes the timing of treatment or protection of plants against these foes easier to target and more likely to be successful.

If, in a few weeks, it feels like spring seems “off schedule,” you won’t need to guess if you’re right. The phenology network’s measurement of the first leaves and blooms, the main indicator of the onset of spring, is also tracked on the site.

Much of phenology is based on the observation of changes of a specific plant, the common lilac in your own yard, for instance, over the course of the year, which is why the phenology network relies on an army of everyday people to share what they see in their own area. These observers log what’s happening to the plants they are watching, hopefully catching crucial developmental moments.

By tracking that same plant over a full season or, even better, year after year, the data and the information that can be gleaned from it improves.

It will be a bit before we see bud break here, but if you’re anxious to keep an eye on when spring might arrive, you can watch the phenology network’s map. And if you want to know when to plant peas, keep your ears peeled for the song of the spring peeper frogs.

You can dig into the phenology network’s data at www.usanpn.org, where you can also sign up to become an observer.