[242] Washington undertook a new landscaping plan and succeeded in cultivating a range of fast-growing trees and shrubs that were native to North America.[243] He also began breeding mules after having been gifted a Spanish jack by King Charles III of Spain in 1784. There were few mules in the United States at that time, and he believed that properly bred mules would revolutionize agriculture and transportation.[244]

Constitutional Convention of 1787
Main article: Constitutional Convention (United States)
Shays' Rebellion confirmed Washington's belief that the Articles of Confederation needed to be overhauled.
Scene at the Signing of the Constitution of the United States by Howard Chandler Christy (1940), depicting Washington as the presiding officer at the Constitutional Convention in Philadelphia in 1787
Before returning to private life in June 1783, Washington called for a strong union. Though he was concerned that he might be criticized for meddling in civil matters, he sent a circular letter to all the states, maintaining that the Articles of Confederation was no more than "a rope of sand" linking the states. 