The first practical question, therefore, was how to employ this labor to the best advantage.

A man of his clear perceptions soon discovered the defects of the system, and he gave great attention to feeding and clothing his slaves, and to their general management.

Parkinson[1] says in a general way that Washington treated his slaves harshly, spoke to them sharply, and maintained a military discipline, to which he attributed the General's rare success as a planter.

There can be no doubt of the success, and the military discipline is probably true, but the statement as to harshness is unsupported by any other authority.
Indeed, Parkinson even contradicts it himself, for he says elsewhere that Washington never bought or sold a slave, a proof of the highest and most intelligent humanity; and he adds in his final sketch of the General's character, that he "was incapable of wrong-doing, but did to all men as he would they should do to him.

Therefore it is not to be supposed that he would injure the negro." This agrees with what we learn from all other sources.