266 animal, vegetable, miracleand peas: “as early as the soil can be worked.” That is a subjective date,
directly related to impatience. I always get stirred up around Saint
Patrick’s Day and go through my annual ritual of trooping out to the po-
tato bed with a shovel, sticking it in the ground, and scientifi cally discern-
ing that it’s still a half- frozen swamp. You don’t need a groundhog for that
one: wait a few more weeks. We generally get them in around the fi rst of
April.
Potato plants don’t mind cool weather, as long as they’re not drowning.
They were bred from wild ancestors in the cool, dry equatorial Andean
highlands where days and nights are equal in length, year- round. They
don’t respond to changes in day length to control their maturity. Other
root crops are triggered by summer’s long days to start banking starch,
preparing for the winter ahead. In fact, onions are so sensitive to day
length, onion growers must choose their varieties with a latitude map.
Temperatures are not a reliable cue—they can rise and fall capri-
ciously during a season, giving us dogwood winter, Indian summer, and all
the other folklorically named false seasons. But no fickle wind messes
with the track of the sun. It’s a crucial decision for a living thing: When,
exactly, to shut down leaf growth and pull all resources down into the
roots to stock up for winter? A mistake will cost a plant the chance to pass
on its genes. So in temperate climates, evolution has tied such life- or-
death decisions to day length. Animals use it also, to trigger mating, nest-
ing, egg- laying, and migration.
But potatoes, owing to their origin in the summerless, winterless,
high-altitude tropics, evolved without day- length cues. Instead they have
a built- in rest period that is calendar- neutral, and until it’s over the tubers
won’t sprout, period. I learned this the hard way, early in my gardening
career, when I planted some store- bought potatoes. I waited as the
weather grew warm, but no sprouts emerged. Potatoes are often treated
with chemicals to keep them dormant, but I’d planted organic ones with
no such excuse for sloth. After about a month I dug them up to see what
in the heck was going on with the lazy things. (I’m much more relaxed
with my children, I swear.) My potatoes were still asleep. Not one eye was
open, not a bump, shoot, or bud.
Now I know: potatoes have a preprogrammed naptime which cannot