If you're cutting through countryside and city in one of those splendid German trains and keep seeing burgher after burgher lovingly patting mounds of dirt in little garden plots, you need wonder no longer. It's one of the rites of spring that mark asparagus season in the Rhineland.
You can confirm this by a glance - or a long gaze - at the special asparagus menu of the panoramic 18th-floor restaurant of the Steigenberger Hotel in Bonn. Choices range from asparagus and ham to asparagus ragout with river crabs and mussels. There are a dozen variations in between, involving soups, salads, Parmesan cheese and vinegar hollandaise or maltaise sauces.
For all of them, the asparagus must be pure white (not green like the cruder American version). And that explains the mound patting and the manpower-intensive prices, which for the Ambassador's Plate at the Steigenberger runs to 40 deutsche marks ($16). As the asparagus grows, so must the dirt surrounding it so the sun's rays never activate the chlorophyll.
On commercial farms whole families - including wives, in-laws, and grandchildren - fan out every morning to pile soft, sandy earth on new tips that are poking through. On the myriad plots at the outskirts and even inside cities, amateur growers who relish this delicacy of the lily family do the same.
The asparagus season runs from mid-May to mid-June. The festivals of the village asparagus cooperatives are held in early May, before the harvesting begins. Now the farmers have no time for such frivolity, since they must constantly monitor their fields and separate the ripe stems from the ones that need another day or two.
This requires a special touch, for the stems are not visible above the earth and must be probed with a trowel-like tool. If the experimental trowel inadvertently cuts too far into a young stem, it can stop further growth. And if sunlight strikes asparagus before it is to be harvested, the telltale green will appear.
Asparagus is sorted into four categories, with the top ''extra class 1 A'' regularized as perfectly even stems 17 to 22 centimeters (about 7 to 9 inches) long.
For the commercial farmer all this effort is worth it. One hectare (2.5 acres) planted with asparagus can bring in 25,000 to 30,000 marks ($10,000 to $ 12,000) a year, or 10 to 15 times more than the same area sown in wheat.
And besides the profits there is the tradition. Family legends and inheritance records alike indicate that asparagus farms go back a century and more on the upper Rhine. They were valuable enough to be given in dowries in the mid-19th century.
As early as three centuries ago, asparagus is said to have had the nickname ''the aristocrat of vegetables.'' The Romans enjoyed a good repast of asparagus. Presumably the Gauls did, too, if one can judge from the present-day title linking asparagus with the Gauls' descendants: ''the delectable vegetable of the French.''
Asparagus takes a lot out of the soil. Cropland must be rotated to produce best. This means three years of preparation, then 10 or 11 years of production, with the best yields coming around the fifth year of harvest.