According to his ideals of continuity and economy of labor, Jefferson preferred to spread the activity of plowing over the whole year and, whenever possible, he tried to make a single plowing serve a double purpose. In 1794, for instance, his rotation plan called for combining the actions of turning under the vetch with the "flush-plowing" for the potatoes and peas.
The Pennsylvania barshare plow was the form Jefferson preferred. A "short and light" one he bought for eight dollars from George Logan of Philadelphia was the model for Monticello's plows. And, from the early 1790s, the moldboard of choice was Jefferson's own moldboard of least resistance. He declared a barshare plow with his moldboard made at Monticello in 1810 to be "the finest plow which has ever been constructed in America."
Jefferson's slaves became accomplished plowmen (and women). They began their training early. Jefferson said that thirteen-year-old Robin "works well at the plough already." The Monticello harvest records indicate that the female farmworkers did some of the plowng. Jefferson's plan for the 1796 wheat harvest reserved eight laborers to "keep half the ploughs agoing": Rachel, Mary, Nanny, Sally, Thamar, Iris, Scilla, and Phyllis. Jefferson wrote his overseer in 1818 that, "when slack of work," the female spinners "might go to the plough."
Among the documented references to plowing found in Jefferson's letters and records are the following:
1775: "A large plough with 4. oxen ploughed 24. furrows half a mile long 10.I. broad & 6.I. deep in a day, which is about 1 1/4 acres."
1793: "Every year, in my rotation, carries either the plough or the scythe through every field."
1796: "Ploughing days have been this year as follows. Jan. 6. Feb. 15. Mar. 20. Apr. 25. May 17. June 19. July 23. Aug. 24. Sep. 20. Oct. 19. Nov. 24. Dec. 10 = 222." 
1798: "If the plough be in truth the most useful of the instruments known to man, it's perfection cannot be an idle speculation" 
1813: "Ploughing deep, your recipe for killing weeds, is also the recipe for almost every good thing in farming. The plough is to the farmer what the wand is to the sorcerer. It's effect is really like sorcery . . . . We now plough horizontally following the curvatures of the hills and hollows, on the dead level, however crooked the lines may be. Every furrow thus acts as a resevoir to receive and retain the waters, all of which go to the benefit of the growing plant, instead of running off into streams . . . . In point of beauty nothing can exceed that of the waving lines and rows winding along the face of the hills and vallies."
1. Memorandum Books, February 8, 1775.
2. Jefferson to Thomas Mann Randolph, August 11, 1793, in Julian P. Boyd, Charles T. Cullen, John Catanzariti, Barbara B. Oberg, et al, eds. The Papers of Thomas Jefferson, v. 26. (Princeton: Princeton University Press, 1950-), 658.
3. Edwin M. Betts, ed., Thomas Jefferson's Farm Book: With Commentary and Relevant Extracts from Other Writings (Princeton: Princeton University Press, 1953. Rep. 1976, 1987, 1999), 54. Manuscript and transcription available online.
5. Jefferson to C. W. Peale, April 17, 1813.