Later he seems to have changed his mind on that point, for near the end of his life he instructed his manager to get the wheat in by September 10th.

Another custom which he was advocating was that of fall and winter plowing and he had as much of it done as time and weather would permit.

All of his experiments in this period were painstakingly set down and he even took the trouble in 1786 to index his agricultural notes and observations for that year.
[4] "On sixteen square rod of ground in my lower pasture, I put 140 Bushels of what we call Marle viz on 4 of these, No.Wt.corner were placed 50 bushels--on 4 others So.Wt.corner 30 bushels--on 4 others So.Et.corner 40 bushels--and on the remaining 4-20 bushels.

This Marle was spread on the rods in these proportions--to try first whether what we have denominated to be Marie possesses any virtue as manure--and secondly--if it does, the quantity proper for an acre." His ultimate conclusion was that marl was of little benefit to land such as he owned at Mount Vernon.
Many of his experiments were made in what he called his "Botanical Garden," a plot of ground lying between the flower garden and the spinner's house.

But he had experimental plots on most or all of his plantations, and each day as he made the rounds of his estate on horseback he would examine how his plants were growing or would start new experiments.
The record of failures is, of course, much greater than of successes, but that is the experience of every scientific farmer or horticulturist who ventures out of the beaten path.