Could warmer temperatures bring an early peak to lilacs this season?

News

ROCHESTER, NY (WROC) – Rochester is highly known around the world for its beautiful display of lilacs seen at the annual Lilac Festival, held in Highland Park every spring. This year the event is safely returning with a new set of dates and safety guidelines.

The dates of the Lilac Festival are typically centered around the average time of year that lilacs will reach their peak in Rochester. The weather has a huge impact on the timing that not just the lilacs will bloom and peak, but when all greenery starts to pop up around the region.

Sometimes the lilacs will peak earlier than they typically do, and sometimes they peak later. There is always subjectivity as to when “peak bloom” really is according to horticulturists, but data of these peak boom dates from Monroe county gives a good idea on when these fates can happen.

History of “peak bloom” in Rochester at Highland Park 

I took a look at what kind of springs Rochester saw when lilacs either peaked earlier than normal, or later than normal. On average, “peak bloom” appears to happen generally during the month of May.

The years where the lilacs peaked later than average were during the month of June and included the years of 1907, 1917, 1919, 1923, 1924, 1926, 1940, 1947, 1956, and 1997. It’s likely that these years had slightly cooler temperatures during the early part of their spring that slowed the blooming process.

There’s one record of an early bloom that occurred on the 29th of April in 1945. Here’s what that spring looked like:

1945

The red shading indicates the range of temperatures that are considered above average, the orange shading shows the normal temperature range, and the blue shading shows the below average temperature range. The narrow blue rectangles all show the range in daily temperatures from the low to the high recorded on those days.

You can easily spot where the range of temperatures fell above normal for a decent chunk of mid March through mid April. This may have easily triggered the onset of lilacs to bloom and peak as early as late April that year.

In recent years, the years of 2010 and 2012 also featured peak blooms that occurred well before the festival dates even started. Their daily temperature data can be seen below and shows a similar trend of above average temperatures during the early spring months.

2010

2010 shows a decent trend of above average temperatures during most of the springtime months barring a few outliers.

2012

March of 2012 really hit the mild mark throughout the entire month of March before jumping back down to normal again by April. A slow warming trend of temperatures then took hold through parts of April that continued into May. Peak blooms for both 2010 and 2012 occurred on May 1st.

How our spring is going so far…

2021

The month of March in Rochester this year fell 5 degrees above average, and got extremely close to making the top 10 warmest March’s on record. You can see how mild temperatures were in the graph above, and that trend has continued for parts of April too.

Could this mean a possible early bloom and peak for lilacs this spring? I’d say it’s very possible given the previous history and our current temperature situation. Of course we’ll have to see how things end up playing out, but early “greening” is already beginning to take place across parts of New England and the southern U.S.

With trends of late blooming becoming less apparent and early blooms becoming more apparent over recent years it begs the question, are springs in Rochester and the northeast getting warmer? Will this affect lilac blooms among other plants in the future?

The U.S. Global Change Research Program states, “Without efforts to mitigate climate change, warming winters and earlier spring conditions under a higher scenario (RCP8.5) will affect native ecosystems and the very character of the rural Northeast.

The group also says that seasonal differences in temperatures across the Northeast have in fact decreased over recent years warming three times faster than summers. It’s predicted that winters will continue to trend milder with fewer extreme cold events, which would cause a shorter and less pronounced cold season. This could then result in a longer transition out of winter into the growing season in spring.

“Warmer late-winter and early-spring temperatures in the Northeast have resulted in trends towards earlier leaf-out and blooming, including changes of 1.6 and 1.2 days per decade, respectively, for lilac and honeysuckle. While unusual winter or early-spring warmth has caused plants to start growing and emerge from winter dormancy earlier in the spring, the increased vulnerability of species to subsequent cold spells is yet unknown.”

Regardless of outcome, the blooming lilacs this season are sure to put on a great show for all to enjoy as we continue through the spring season.

~Meteorologist Christine Gregory

Copyright 2021 Nexstar Media Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.