Look for an Evergreen Day

What the day is

Look for an Evergreen Day is observed on December 19. In the week of the solstice the evergreens are the only thing still green in much of the northern hemisphere, which is most of why they ended up in midwinter tradition.

Origin and background

The origin of the observance is not documented.

The botany is better than the folklore. Winter is a drought as far as a plant is concerned, because water locked up as ice cannot be drawn through the roots. A broadleaf tree solves this by shedding its leaves, since broad thin leaves lose water far too fast to keep through a season when none can be replaced.

Conifers solve the same problem by redesigning the leaf. A needle has very little surface area for its volume, a thick waxy coating, and stomata sunk into pits along its length, all of which cut water loss to a level the tree can sustain. The tree pays for that with less efficient photosynthesis, and gets back the ability to work on any mild day rather than only in summer. That trade wins in cold places with short growing seasons and thin soils, where building a complete new set of leaves every spring is an expense the tree cannot easily meet, which is why conifers dominate the boreal forest.

Two common assumptions are wrong. Plenty of evergreens are not conifers, including holly, ivy and rhododendron. And some conifers are not evergreen: larch, bald cypress and dawn redwood all turn color and drop their needles every fall, which regularly convinces people their tree has died.

The conical shape is doing work too, shedding snow that would otherwise break the branches.

How to take part

• Go and look at one properly. Compare a pine, a spruce and a fir, which most people cannot tell apart.
• Count needles per cluster to identify pines, which is the quickest field distinction.
• Look for a larch and notice a conifer that is completely bare.
• Crush a needle and smell it. Fir, spruce and cedar are distinct.
• If you buy a cut tree, keep the base in water from the day it arrives.