Spring equinox: Our equal hours of day and night begin their upswing toward the light on the morrow, at least for us (opposite, of course, in the Southern Hemisphere). Yet there are a variety of different modes of parsing “springtime.”
The spring months for us of March, April, and May only partly track the March 20 (11:33 am) to June 21 (12:21 am) official spring this year. Spring months for Australia are Sept. 1 to Nov. 30; if you are Irish and follow the Gaelic calendar, the three spring months are February, March and April; In Sweden, at least according to Wikipedia, meteorologists “define the beginning of spring as the first occasion on which the average 24-hour temperature exceeds zero degrees (Celcius) for seven consecutive days, thus differing by latitude and elevation.” Very fluid, I must say.
Then there are the “harbingers of spring” as defined by temperature, growing degree days and phenology.
Now is the time of year when “phenology” is most fun and functional. As Dan Herms, vice president of research and development at The Davey Tree Expert Co. and formerly chair of the Ohio State University Entomology Department, defines it: Phenology “is the world’s oldest science; the foundational science of human existence.”
So, what is it? In broad terms it is the “study of recurring biological events,” the way that early harvesters and gatherers and then farmers figured out when to plant: It matches biological phenomena with triggering environmental conditions, predicting bird migrations, seed germination, when plants will flower .
It is the ultimate in “harbingers of spring,” and it is predictable. For example, plant flowering and insect development (such as egg hatch) are driven by heat units, by the accumulation of growing degree days that have occurred for the season.
Amazing, if obvious, but true — and predictable. From knowing how many degree-day units have developed so far this year and will develop if short-term weather predictions are roughly true, we can predict when specific plants will flower and when specific insects will emerge.
And we have a wonderful tool, the Growing Degree Calendar developed at OSU in Wooster by Herms, Denise Ellsworth and Dave Lohnes.
Here’s an example of how to use the calendar (Google OARDC + phenology): If you inserted Wooster’s ZIP Code (44691) this past Sunday you would find that growing degree days (GDD) to date were 35. (More on that later.) Since the number of GDD was 35 and since the first flowers of silver maple bloom at 34 GDD, you would know (and observe) that silver maples are now starting to bloom. What is next: Cornelian cherry dogwood first bloom is 40, red maple first bloom is 44, Japanese pieris is 60, star magnolia is 83.
So, how are these growing degree days compiled? It can be a bit complicated, and there are several systems. But one easy way that essentially works is this: Add up how far above 50 degrees F the days have been this year, and then divide that number by 2. For example, a 60-degree high day would accumulate five growing degree days (60 – 50 = 10; and then 10/2 = 5 GDD).
No degree days are added if the temperature is not above 50. So if you added up all the degree days so far this year, you’d find that as of Sunday, Wooster had 35 GDD. And silver maples in Wooster have just bloomed. Incredible, but true. Mix this with insect development, for example, and you can see how useful this is for estimated plant pest control strategies (eg, gypsy moth egg hatch is at 192 GDD).
Predicting plant and insect development is fun “citizen science” for all ages.
Weather is of course somewhat unpredictable, but short-term temperature predictions are fairly close. For example, high temperature predictions on my phone’s Weather Channel App for this week for Wooster are:
• Sunday – 41 (adding zero GDD)
• Monday – 55 (55 minus 50, divided by 2 = adding 2.5 GDD)
• Tuesday – 57 (3.5 GDD)
• Wednesday – 63 (6.5)
• Thursday – 68 (9)
• Friday – 58 (4)
• and today, Saturday – 53 (1.5).
Therefore, last Sunday I would have predicted that today there would be 35 + 2.5 + 3.5 + 6.5 + 9 + 4+ 1.5 = 62 growing degree days. And as of Sunday, I could have predicted that red maple first bloomed by midweek and that Japanese pieris first bloomed yesterday or today. Try it; you’ll like it.
There’s more information at weather.cfaes.osu.edu/gdd and more fun at the USA National Phenology Network. It will really help when the time approaches for crabapple bloom at OSU’s Secrest Arboretum in Wooster later in April — keep track of exactly when and predict it as it approaches!
Hazelnut trees and shrubs are not to be confused with the winter-blooming witch hazels (Hamamelis vernalis and various hybrids with Asian witch hazels) that began blooming in early March at Secrest Arboretum in Wooster.
Hazelnut/filbert species just started to bloom the past two weeks in Northeast Ohio. They are monoecious, with male and female flowers on the same plant, but not in the same blossom. The 2-4” staminate flowers (catkins), are filled with pollen that is not yet ripe, only later to create a powdery yellow cloud to pair with the tiny vermilion-colored female stigmas that now sit atop buds on nearby twigs.
There are 15 species of Corylusincluding the common native hazel of woodlands, Corylus americanum, a shrub, and the non-native C. avellana shrub, the source of the delightful hazelnuts we eat.
Ah, the memories of small bowls of hazelnuts at a lunch with Oregon nurserymen a decade ago; the best of the best Ritter Sport chocolate bars with whole hazelnuts; hazelnut pastes mixed with chocolate in everything from fine chocolate gianduja (invented in Italy during Napoleon’s rampaging reign) to Kinder Bueno candies and Nutella spread.
There are also several hazels in the ornamental horticultural trade, including Corylus fargesii, a lovely small tree that’s becoming more popular, and the Harry Lauder’s walking stick, C. aveallana “Contorta,” a shrub with a twisted stem, known as contorted filbert.
The hazels at Secrest are trees, yielding the tiny harbinger of spring vermilion stigmas and are Turkish filberts (C. colurna) with their extravagant turban-like fruits. Stephen Tomasko, David Wiesenberg and I make a late winter pilgrimage to see them each year southwest of the Shade Tree and Taxus plots. Corylus is in the birch family, the Betulaceae, along with birches, alders, hornbeams, hop-hornbeams and hazel-hornbeams, all with this monecious flower arrangement.
To conclude our notes on hazels, with a nod to our discussion of phenology, let’s take a look at Henry David Thoreau’s musings of the wild flowers of Corylus americanum, with some of his 1850s phenological notes from his Concord, Massachusetts, haunts, compiled in the book “Thoreau’s Wildflowers.”
A March 23 entry from Thoreau: “The crimson-starred (female) flowers of the hazel begin to peep out though the catkins have not opened … March 27, the hazel is fully out … April 13, for two or three days I had given the hazel catkins (male) a fillip with my finger under their chins to see if they were in bloom, but in vain – but here on the warm side of the wood, I find one bunch fully out and completely relaxed… Aug. 8, the squirrels are now devouring the hazelnuts fast… Oct. 27, I love to be reminded of that universal and eternal spring when the minute crimson-stained female flowers of the hazel are peeping forth on the hillsides. When nature revives in all her pores.”
End Note: But what of Part II of dandelions from John Cardina’s “Lives of Weeds,” promised last week. Never fear, dandelions will never die. Another time.
Jim Chatfield is a horticulture educator and professor emeritus at Ohio State University Extension. If you have questions about caring for your garden, write to [email protected] or call 330-466-0270. Please include your phone number if you write.