Reed PughWhy this spring seems late. But is it?

Do you remember last spring…it came all at once in a massive explosion of color, leaves and pollen. Snowdrops, Squill and Daffodils all came at the same time, while Maples flowered and dispersed their pollen. During the last week of March in 2012, Forsythia, PJM Rhododendrons and Star Magnolias were already in full bloom and my tree lilacs, an early tree to leaf out, were already in leaf. However, this year you have to search hard to find any buds swelling and only this week did Squill start to appear and Daffodils start showing flower buds.

Snow drops finishing with rock iris going strong and daffodils and squill starting to come

Snow drops finishing with rock iris going strong and daffodils and squill starting to come

Why the dramatic difference from one year to the next?  The answer comes in three words– Growing Degree Days (GDD).  By tracking this measurement you can tell when plants will flower and when the bugs will hatch. While the calendar is a good guide for Baseball’s Opening Day, there can be quite a variation when it comes to plants and insects, since they go on their own calendar that is based upon weather and temperature.

Squill (Scilla siberica) loving the sun

Squill (Scilla siberica) loving the sun

One GDD is equal to the number of degrees the average daily temperature is above 50 degrees. You take the average of the high and low for the day and subtract 50.

(High Temperature + Low Temperature) / 2 – 50 = GDD

You can do it yourself or rely upon your local State School Extension. I use UMass — click on the Landscape Message tab for timely updates.

Serviceberry (Amelanchier canadensis flower buds emerging - it should flower at 75GDD

Serviceberry (Amelanchier canadensis flower buds emerging – it should flower at 75GDD

This season we haven’t had many warm days and the evenings have remained very cold, so as of today, April 5th we have had a paltry 1.5 GDD for the season. Last year we had 103 GDD by the end of March. These numbers seem small since last year we accumulated nearly 3,300 GDD, but a lot of activity happens in these first couple hundred GDD. Late in the summer with 90+ degree days and warm nights we can add 300 GDD in a week, while in some years we may only accumulate a total of 300 GDD by the end of May.

So, is spring late this year or were we early last year? I pulled some annual information from UMass and looked at GDD and soil temperature for the last 10 years.

Saucer magnolia (Magnolia soulangiana) swelling slightly but holding tight - should flower at 50-75GDD

Saucer magnolia (Magnolia soulangiana) swelling slightly but holding tight – should flower at 50-75GDD

 

Year     GDD     Soil Temp

2013     1.5         48
2012     103        49
2011     12          42
2010     20          44
2009     3            49
2008     19          36
2007     35          35
2006     17          39
2005     0            32
2004     17          37

 

The data reveals that we might be a little late this year when compared to the past decade, but last year was most definitely early. With all the late snow we had this year maybe we are just hoping for spring to come. By this time last year we had already had three good weeks of spring. I remember that I had mostly cleaned up and prepped my gardens by the end of March. That is certainly not the case this year as I still have a chunk of snow in my back yard.

Andromeda (Pieris japonica) just opening some flowers - should flower around 50GDD

Andromeda (Pieris japonica) just opening some flowers – should flower around 50GDD

One of the nice things about spring coming slowly is that the flowers are nicely spaced out and last longer in the cool weather. The later that Magnolias flower gives them a better chance of lasting, as they get easily burned with frost.

The dreaded Winter Moth that is devastating many of our shade and ornamental trees emerges within the first 50 GDD, and last year the arborists had already sprayed once for the moth and this year they are just waiting for the plant and insect world to waken from its slumber.

My lovely with hazel entering its 3rd month of flowering but I know its days are numbered

My lovely with hazel entering its 3rd month of flowering but I know its days are numbered

During the first 50 GDD you can expect to see PJM Rhododendrons, Forsythia, Star Magnolia and Pieris starting to flower. It is also the time that the Witch Hazels finish and drop their flowers. My Witch Hazel is still in bloom, lasting more than two months and without the heat the flowers have stayed fresh, and will be around at least for another week or two.

At 100 GDD you start to see the native Dogwood (Cornus florida) and Crabapple flowers. Check out this Cornell IPM Fact Sheet on flowing times for plants.

No matter how much you analyze, hope or pray, spring will come when it comes and there is nothing I can do about it.

Like this post? Why not share it with a friend?


Reed Pugh

About Reed Pugh

Horticulturist and landscape designer living in the suburbs of Boston, Massachusetts. Reed is passionate about gardens and plants and loves writing about horticulture, plants, garden accoutrements, best garden practices and whatever else comes to his frenetic mind. He tries not to take himself too seriously but has been known to 'geek out' on occasion. Reed, and his company Barking Dog Gardens, can be found at Reeds Garden Ramblings

3 thoughts on “Why this spring seems late. But is it?

  1. hal.farsed on said:

    Interesting I guess – but as this is not a site with readers exclusive to the United States, how about using measurements that the majority of the world uses and understands?

    • Reed’s blog is republished on GardenDrum from his own blog site Reed’s Garden Ramblings which is written for his USA New England audience. I usually remember to add in temperature conversions for the metricated, but since I accidentally got my car thermometer display stuck on degrees F and now feel comfortable whenever the temperature is in the 70s, I’ve forgotten a few times.

  2. Thanks Reed. The message is nature calls the shots about the arrival of the seasons, not the calendar. We are having unseasonal rain in southeast Queensland, Australia, in what should be our dry autumn … think the world has turned upside down.

Leave a Reply (no need to register)