Crow’s Nest: Late frost and sensitive fern

May 20, 2023

By Daniel Barringer, Preserve Manager.

Flat fronds of sensitive fern

Photo: Daniel Barringer

We usually consider May 15 to be our last likely frost date, but this year (early Thursday morning May 18) we definitely experienced freezing temperatures, at least in open and low-lying areas. (The forest canopy shields vegetation below it a bit, and cold air sinks.) This is not the first time we had frost after May 15, and gardeners were busy spreading bedsheets over their vegetables on Wednesday evening.

One of my favorite plants is sensitive fern, Onoclea sensibilis. It is called sensitive fern because although it is a perennial plant, the foliage is sensitive to cold and will die back from frost. Usually this makes it the first plant to succumb to the season in the fall, but it also can set the growth back in the spring. Our sensitive ferns had already died back once from a frost earlier this spring after they had leafed out. Then it happened again: by Thursday afternoon a large patch in a wet meadow had turned brown. But in sheltered areas it still grows unscathed; the photo above was actually taken later in the day than the one below—just in a different location. And most likely the plants whose leaves died will grow back quickly again this spring.

Sensitive fern that has been killed by late frost

Photo: Daniel Barringer