Why did slaveholders depend on slave labor?

Answer 1

Agriculture in the South was labor intensive, from rice farming in South Carolina to cotton (which came later to the region). It took large numbers of workers, all in one place, to harvest and process crops. There were not enough settlers already in these regions, and getting them to do the hardest labor would have meant huge expenses in housing, salaries, and organization.

So the "free" labor of slaves was used. Slaves still had to be fed and housed, but had no control over where they lived, where they went, or what they did. This made them indispensable for all sorts of farming activities. The fact that they often had children (born into slavery and eventually adding to the labor pool) was offset somewhat by the requirements of caring for the babies and children. Until the mid-19th century, slavery was a generally accepted custom.

Answer 2

They relied on slave labor because the crops they raised, such as cotton and tobacco, were labor intensive. Having plenty of labor that was not paid was very economically successful.