Andrea Wulf's book "Founding Gardeners — The Revolutionary Generation, Nature and the Shaping of the American Nation" is published by Knopf.

As America's gardeners dig, plant, weed and grow lettuce, beans and tomatoes in their vegetable plots this summer, they are part of a tradition that harks back to the beginnings of the United States. Just by working on a compost pile this weekend, you'll be in good historical company.

The first four presidents of the United States — George Washington, John Adams, Thomas Jefferson and James Madison — were all utterly obsessed with manure and recipes for compost. Adams even jumped into a stinking pile when he was America's first "minister plenipotentiary" to Britain in London in 1786. Teasing apart the straw from the dung (clearly not minding the muck on his hands), he declared with glee that it was "not equal to mine."

Washington, Adams, Jefferson and Madison regarded themselves first as gardeners and farmers, not politicians. They wove their passion for gardens and nature into the fabric of America; it was aligned with their political thought. Agriculture would be the foundation of the new republic, they believed.

"Cultivators of the earth," Jefferson wrote, "are the most vigorous, the most independent, the most virtuous." The greater the proportion of husbandmen, Madison believed, "the more free, the more independent and the more happy must be the society itself."...