Bostonian foliage (photo by Kirk Fernandes)

Bostonian foliage (photo by Kirk Fernandes)


How to Make Harvest Time Anytime

by Karen Rowan

When summer’s heat and humidity begin to give way to cool, crisp air, I look forward to one of nature’s most enthralling sights:  New England’s fall colors.  When the shades of gold and crimson emerge, I take in as much leafy glory as I can.  The problem is, it never lasts long enough. 

Modern technology has given us the ability to break some of Mother Nature’s rules and beat the seasons.  I can get fresh tomatoes any time of the year; if I went to Dubai where there is no winter, I could ski down indoor snow-covered slopes, when it’s over 100 degrees Fahrenheit outside.  So could I create my own little perpetual autumnal world, teeming with auburn delights, to enjoy whenever I want? 

It turns out, its possible to purposefully incite the trees to muster up their colors.  All I would need is a greenhouse in which I could tightly control the light, temperature, and humidity levels, says Boston University biology professor Richard Primack.  The trick to conjuring up the visual thrills of harvest time, anytime, is to mimic both the drop in temperature and the shortening day length of September.  

It’s not just the fact that the days are shorter; they must also be gradually decreasing in length in order prompt the leaves to change.  More accurately, it’s the gradually increasing periods of darkness that affect the trees biological clocks.  In plants, molecules called phytochromes, which change their shape when struck by light, control circadian rhythms and the timing of flowering.  It would be possible to outsmart the phytochromes, though, and trick them into making a false fall.  The biggest problem would be making sure there is enough light, because the intensity of sunlight at any time of the year is hard to imitate, says Primack. 

Fabricating autumn’s temperatures would also be challenging.  It’s not a precise science because the natural temperatures vary greatly from year to year.  In a greenhouse, the conditions would have to match the sharp differences between day and night temperatures, which are greater in the fall than in the summer.  So if I could engineer my greenhouse with the exact lighting and temperatures needed, will I have set the stage for producing my designer-knock-off version of autumn? 

Not exactly, says Maciej A. Zwieniecki, of the Arnold Arboretum of Harvard University.  A critical component would still be missing – the developmental stage of the leaf.  Leaves must reach a certain stage of their maturity before they can produce their colors.  Zwieniecki says that the shortening days and falling temperatures of autumn trigger the breakdown of an enzyme called rubisco.  Rubisco’s summer job is to assist in photosynthesis.  In the fall, the breakdown of rubisco produces free radicals, which can damage the genes and proteins of leaf cells.  Leaf pigments protect the plant from the assault of the free radicals, much like sunscreen protects our skin.  But only mature leaves can produce pigments, if leaves that are too young are subjected to autumn’s conditions, they would just die unceremoniously. 

So I might be able to beckon the colors to come to my greenhouse in August, when the leaves have reached their prime.  But June, with her immature leaves, simply won’t play hostess to ruby and amber.

Most sadly, there is no way to make the colors last any longer.  Once the process of color change has begun, the colors will inevitably run their course, and the leaves will wither and drop, Zwieniecki says. 

And maybe, for all of my scheming, nature has the last laugh.  I’ve spent this gorgeous day inside, dreaming up wily ways to summon up a sight that is just outside my door, right now.