Flowering Plants and the Summer Solstice

For those of you that may not be keeping track, this year the Summer Solstice occurs June 21st at precisely 9:54 a.m. MDT (obviously, I ‘m keeping track). The Summer Solstice marks the beginning of summer in the Northern Hemisphere, and the sun's most northerly point in Earth's sky. “Solstice” comes from the Latin word for “sun stand still” because the sun will reach its highest point at noon on that day and briefly appear not to move.

People from cultures all over the world have held solstice celebrations for thousands of years. Traditionally people celebrated renewal, life, fertility, and the potential for a good harvest on the summer solstice. Today people around the world still celebrate the arrival of summer with outdoor feasts, singing, dancing, bonfires, and of course gardening!

How do you celebrate the Summer Solstice? 

Stonehenge in England is thought to have been constructed to celebrate the summer solstice. To this day, tourists flock to the ancient site to witness the sunrise right through the center stone during the summer solstice. Perhaps you are familiar with the pyramids of Chichén Itzá on Mexico’s Yucatán Peninsula? The precise construction and engineering of these pyramids create a visual display twice a year in which the central pyramid of El Castillo is bathed in pure sunlight on one side and full shadow on the other. Closer to home in Fairbanks, Alaska their Summer Solstice celebration includes a Midnight Sun Festival and Baseball Game. Even closer to home, the Scandinavian Midsummer Festival in Estes Park, or similar summer solstice celebrations are held in Evergreen, Colorado Springs, and Beaver Creek.

For Colorado residents, the Summer Solstice will gift us with 5 hours, 27 minutes more day light than we will experience on the December Solstice on December 21st.  With this extended daylight, it is easy to spend more time enjoying gardening.

Speaking of Gardening

Have you ever wondered how day length affects plants and why they bloom when they do?  The key is a physiological response in plants called Photoperiodism. Simply put, Photoperiodism is the development of plants to the relative lengths of light and dark periods. All plants fall into one of these three photoperiod classifications: short-day plants, long-day plants, and day-neutral plants.

One of the most well-known examples of a short-day photoperiod response plant is Poinsettia.  A general rule of (green) thumb is that when the dark period reaches a minimum 11 hours, 40 minutes, the Poinsettia flowers will initiate. The colorful Poinsettias that are available at our local garden centers for the winter holidays have likely had their dark photoperiod (nighttime) artificially extended in early fall to meet the nearly 12 hours of darkness, so they will have the expected appearance for our holiday décor.

A tasty example of a day-neutral plants is an everbearing strawberry. Not all strawberry plants are day-neutral, however to extend the harvest of your strawberries, consider planting day-neutral or everbearing strawberry plants as they will continue to produce fruits the entire growing season regardless of daylight length.

‘Black-eyed (or brown-eyed) Susan’ (Rudbeckia fulgida ‘Goldstrum’) is an exceptional example of a long-day herbaceous perennial. Flowering non-stop from July through the September, this local favorite with its large, golden daisy-like blooms and brown-black centers, are the backbone of perennial borders and provide late season nectar for pollinators.

What are your favorite short-day, day-neutral or long-day plants?

Allison Gault