Summer Solstice

At summer solstice, sunlight floods our northern latitude. This annual milestone on June 21 is the high water mark for plant growth in northern forests. The 5 am sunrise and after-8:30 sunset delivers more than 15 hours of daylight. It’s hard to sleep with so much going on outside…

Trees are growing at their fastest annual rate. Sudden shade indicates the race to capture light to make food is underway. Fresh young leaves harness long hours of daylight to make sugars to fuel growth or to be stored as more stable starch next winter in roots.

Picture the cut end of a log: the majority of each annual growth ring is light-colored “spring wood.” Tiny tubes, like miniature drinking straws inside the bark, conduct water from the soil to leaves.

The dark-colored part of an individual growth ring is “summer wood” of even-smaller tubes formed when growth slows by mid-summer. Next year’s maple syrup crop is already well-underway in the early leaves of sugar maples.

In fact, all trees are subtly preparing for next winter, forming tiny new buds for next spring at base of each leaf stem. The summer buds are also an insurance policy in the event of insect attack. If a gypsy moth caterpillar infestation were to completely defoliate oaks, they can re-foliate using leaves from summer-formed buds.

The relatively short growing season means sunlight is the most important annual limiting factor to plant growth, assuming ample water and soil nutrients are also available.

June’s the right time for catching rays. So make like a tree: soak up the sun!