Charlemagne had a shovel in every monastic garden, or so it seems:*
As early as the days of Charles the Great (Charlemagne) the cloister owned outside property, and just as at Canterbury we must conclude that the plan of St. Gall meant the orchards and vineyards to be outside. The whole time of Charles the Great— and the St. Gall plan may be supposed to belong to it — was of great importance for horticulture. Charles himself encouraged personally the cultivation of his own estates, and in his private garden he had a large number of new plants, chiefly of course for the kitchen and the workshop. The Capitulare de Villis vel Curtis Imperii Caroli Magni” [another version HERE] (which contains among much else a very complete list of woods useful for building) had an unimagined influence on the arts of architecture and horticulture. The great ruler specially favoured the extension of monasteries, and he had them built wherever he could. Thus, in the full enjoyment of peace and protection, the monks busied themselves very diligently with the gentle art of gardening, and so reaped calm happiness and the useful fruits of the earth. There were some, to be sure, who detected a danger in this pleasure. In a work by Herrad of Landsperg, called Hortus Deliciarum, the author tells of a recluse who has climbed up to the very top rung of the ladder of Virtue, but then looks behind him. There he beholds his flowery garden, he is seized by a strong desire, and plunges headlong down among the beds, because he has preferred the earthly to the heavenly paradise (Fig. 126).
In other words, we owe a huge debt to Charlemagne, who encouraged the spread of herbs across Europe, most grown in monasteries if the weather permitted.
Doesn’t it send chills up your spine to think that purslane, also called pigweed, now so popular in Californian farmers’ markets, dates back to early buddings of Western culture? (Various accounts claim it originated in China or India). In De arte phisicali et de cirurgia of Master John Arderne, surgeon of Newark [England], dated 1412, Arderne states that purslane will cure people of the thirst for alcohol:
Do this against thirst. Let him eat cucumber seeds, purslane, lettuce, sorrel and orach, equal parts of each.
A Syrup:—
Juice of sorrel, lettuce, purslane and mallow. Make a decoction and add half an ounce of tragacanth and make a syrup with sugar. If he is still thirsty after taking the medicine nothing is so good to give as chicken broth.
I think I’ll pass, the wine bottle, that is! Wine, another monkish modification.
*Commentary from History of Garden Art, by Marie-Luise Gothein (1913, first published in German).
CYNTHIA D. BERTELSEN 
I did run across references to this and meant to check it more later. So thank you for letting me know that, indeed, purslane existed on this side of the pond before the contact period.
Some species of purslane (Portulaca oleraceae, at least) are also native to North America. Lots and lots of carbonized purslane seeds have been found in archaeological sites dating to 200 AD to historic times (when it was eaten as a potherb and used medicinally).
It’s one of the few plants with lots of omega-3 fatty acids in it. Unfortunately I only really like its taste when it’s been fried in bacon grease. :-/
The story of the monk gazing back at his garden is wonderful!
I’m really liking this topic! Thank you so much for sharing this source. I’m going to have look this up.
Coincidence: I just read this “According to tradition, Charlemagne owned a vineyard on the Cote d’Or…” It’s now “the famed Corton-Charlemagne, vineyard, which still produces one of the world’s most sought-after white wines.” From “The Judgment of Paris,” p. 26.