If you’re dirt poor, you’re suffering extreme poverty, lacking most of the necessities of life.
According to the Oxford English Dictionary, “dirt poor” is an American expression first documented in the 1930s, during the Great Depression, and refers to the Dust Bowl.
As a side note, “dirt” as a synonym for “soil” is an American invention. The following phrases were all coined in the United States: dirt farmer, dirt road, hit pay dirt, eat dirt, and do someone dirt.
The phrase implies that poor people lived in houses with dirt floors, but not all of them did so. In the poorest houses, the floor might be packed dirt, but those who could afford them had wooden floors. In reality, the phrase originates with the dust storms of the Great Depression.
“Dirt poor” first appears in print in Edna Ferber’s 1931 novel, American Beauty. During the Dust Bowl era, thousands of Great Plains farmers lost everything except the dirt of their unworkable farms, now worthless. Then huge dust storms made sure that they even lost the dirt needed to grow crops. Of course, these dust storms also created an unusual amount of dirtiness, blowing sand and dust into every corner of their buildings and heaping it over abandoned equipment.
I’ve seen photographs of the dust-blown abandoned farm buildings, and of the hungry people who had to leave them. Those pictures are a poignant reminder that humankind has no control over nature.