Adapted in part from an article by Dr. May Berenbaum that appeared in Horticulture magazine in July 1980. Information about her related works is located at http://www.life.uiuc.edu/Entomology/faculty/berenbaum.html
Parsley, Petroselinum crispum, is a member of the family Umbelliferae. Also included in this family are parsnip, celery, dill, carrot, lovage, and a number of other well-known herbs and vegetables. The name "Petroselinum" is derived from the Greek word "petros" which means "stone," referring to the plant's habit of growing in rocky places. "Selinon" was the Greek word for parsley in ancient history.
Parsley garnishes platters containing everything from burger to filet mignon. It is a common sight today and inspires no great emotions. However, there was a time when the sight of it was enough to rout an entire army. According to Plutarch, a Roman historian who lived during the first century AD (ca. 46-119), an ancient Celtic ruler with a pitifully underequipped militia exploited the Greeks' fear of parsley by sending hundreds of asses blanketed with parsley to greet the advancing Greek troops. At the sight of the parsley, the superstitious Greeks turned and fled, and the Celtic kingdom was spared an invasion.
Dr. Berenbaum, University of Illinois Entomology Department head, stated in her article:
Parsley is slow to germinate, and it does germinate inconsistently, requiring anywhere between three and six weeks. Even today, the germination of parsley seeds seems a bit mystical. Recommendations frequently encountered on the back of seed packages or in gardening catalogs include washing or soaking the seeds in water before planting. A scientific study of the chemistry of parsley seeds provides some insights not only into the utility of washing or soaking the seeds before planting, but also into the superstitions and beliefs of medieval gardeners.
Parsley contains chemicals called furamocoumarins in the seed coat. Because furanocoumarins prevent weed seeds from germinating, the home gardener won't have to weed parsley quite as often as other plants. But there is a complication--the same furanocoumarins also may interfere with the germination of the parsley itself.
With furanocoumarins in mind, some of the superstitions surrounding parsley planting don't seem so outlandish. The differences in the number of visits to the Devil that seeds were said to make might very well have reflected the variation in germination time due to local differences in soil moisture. As for male heads of households waiting for Good Friday to plant the seeds, ostensibly to propitiate the Devil, it's a sound idea in any case to plant in late March or early April, when the spring showers are plentiful.
Soaking the seeds overnight will reduce to some extent the month-long germination period. Seeds should be thinly distributed and planted no more than one-half inch to one inch deep, and seedlings can be thinned to approximately six to eight inches apart when they are an inch high. Some people like to mix in seeds of a plant that germinates rapidly--radish, for example--so that the row isn't inadvertently trampled or replanted during the month-long wait for seedlings to appear.
Once parsley is mature, picking the outer leaves first guarantees that the plant will keep growing. Parsley overwinters beautifully; the frozen plants can be dug out of the snow and thawed for use, although the plain-leaved varieties survive the freezes better than the curly leaved varieties. A biennial, parsley will flower and set seed if left undisturbed during its second year of growth. Perhaps due to its furanocoumarin content, parsley is rarely bothered by insects. One notable exception is the black swallowtail caterpillar (Papilio polyxenes), which perversely eats only plants that contain furanocoumarins. The black swalltail caterpillar is seldom numerous enough to cause much damage and is easily controlled by spraying with diazinon, carbaryl (Sevin), or Bacillus thuringiensis, or by handpicking.
Parsley, then, is hardly a devilish herb. On the contrary, a good source of vitamins A and C, high in calcium,niacin, and riboflavin, and invaluable in seasoning and garnishing, it is today regarded in some kitchens as a godsend. Modern phytochemistry has lent credence to the substance of the superstitions--the erratic nature of germination and the importance of planting time--but has replaced fear and ignorance with plant chemistry. There are, however, a few mysteries remaining. Not even furanocoumarins can account for the difficulties medieval virgins encountered while planting parsley.