TOLEDO, Ohio — March 20 marks the vernal equinox, also known as the first day of spring. While increasing average daily temperatures promise the end of winter, some of the greener indicators are still on hold. While the first leaves have yet to appear on northwest Ohio trees, they aren't late, according to scientific data. Here's what you can expect to see from local flora in the coming weeks.
The USA National Phenology Network (NPN), an organization dedicated to the study of cyclic and annual climate and plant phenomena, provides data on first leaf, or "leaf-out" dates from 1981 to present.
As different species of plants sprout their first leaves of the season at different dates, NPN marks the first leaf date by the appearances of the first leaves on the two types of honeysuckle and lilacs. These three species have some of the earliest average first leaf dates in the U.S., meaning their foliage is a good indicator of the very first signs of spring.
While this data accounts for only a few select plants, they can point to how soon other species will follow.
The first leaf date for an area varies across the country: in warmer climates and at lower altitudes, leaves will generally appear earlier in the year, while in colder climates and at high altitudes such as mountains, leaves can appear as late as June.
In Toledo, the average first leaf date using data from 1990-2020 is April 4. During some years, the leaf-out date can occur much earlier or much later. Between 1981 and 2022, the earliest leaf-out date in Toledo was March 16 in 1990; the latest was April 19 in 2018.
However, data indicates many regions across the country are experiencing earlier first leaf dates than average. Since 1982, four of the six earliest leaf-out dates in Toledo have occurred in the last 10 years.
U.S. EPA research states a national trend of earlier leaf-out dates gestures to the increasing role climate change and global warming are playing in our environment: the milder the winter season, the sooner trees and other annual plants will sprout leaves.
When will the first leaves of 2023 arrive?
While there isn't a way to know precisely, NPN data indicate southern Ohio has already had their first leaf date as of March 17. According to NPN, honeysuckle and lilac have started growing leaves in this region 20 days earlier than a 30-year average. As the days progress, trends indicate northwest Ohio will see its first leaves at either an average or earlier-than-average date of April 4 or earlier.
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