Why did plantation owners begin to import African slaves to work their farms?
They had tried to use Indians and indentured servants but it did not work
African slaves were seen as the best labor force for plantations since Owners had tried to use Natives or indentured servants as their workers but were less successful.
The work was very hard and could be fatal. Of those who didn't die, Indians would just leave, disappearing into the forest. The indentured servants employment terms were found to be too short and often had a costly final payment attached to them. They would also occasionally just disappear. Indentured servants had some legal rights under the law. Employers were often obliged to feed them adequately and keep them "healthy".
Slaves had fewer options and no rights. Disappearing was harder since most black people were slaves and thus prone to re-enslavement and harsh punishment. Slaves would often grow their own food if given the chance.
It is what drove plantation owners to import so many slaves until Jefferson forbade it in 1808, importations continued illegally though.