Saturday, February 3, 2018

Crocus already? Too early?

Crocus leaves in Lakewood, 1/17/18
It’s early February and some crocus are already emerging. In fact, crocus leaves appeared in my yard in mid-January. What’s going on?

An early bloom certainly isn’t unprecedented in Denver and Jefferson County. The National Phenology Network (NPN) collects reports on the status of plants around the country and combines them with weather data to create models of where spring has sprung. Just last year, data from the NPN indicated that Denver’s plants were blooming up to three weeks ahead of the average for 1981-2010.

According to Dr. Anna Sher of the University of Denver, this is a signal of a warm winter – and part of a century-long trend. “The fact that the temperatures have been warming on this planet, and the implications for the timing of spring are well-documented and well-known by scientists. For many flowers here in Colorado, we’re seeing plants blooming almost a month earlier now than a hundred years ago.”

Her team knows this because they’ve been examining archives of dried and meticulously logged plants that go back many years. An early bloom can be harmful for plant life. Though it’s getting warmer earlier, the date of the last frost hasn’t changed nearly as much, Sher said. As a result, some early bloomers might be hurt or killed by cold temperatures. Changes in the schedule also can throw pollinators, such as bees, out of sync. Net effect: disruption of the ecosystem.

We know that winter isn’t over yet. March is typically our snowiest month, and we had a late freeze in 2017 that disrupted many spring-blooming plants. For now, it’s just watch and wait. This overly eager foliage can be damaged by extreme cold and drying winds, and may cause the tips of the leaves to turn brown. As long as the flower buds stay below ground, they are well protected from cold. If they rise above the soil surface, you can add a layer of mulch to help protect them.

Information excerpted from Denverite Newsletter, March 2017.