Do beets cause kidney stones?

Possibly: If you have a tendency to form oxalate stones then food rich in oxalates like beets could contribute to stone formation.

Beets and stones: Beets are rich in oxalate; calcium oxalate forms 80% of stones in adults; many foods contain oxalate, only nine foods are believed to increase importantly in the urine and then promote kidney stone formation. They are: beets, spinach, rhubarb, strawberries, nuts, chocolate, tea, wheat bran, and all dry beans It is best to avoid these foods. Drinking 3 to 4 liters per day of fluid is essential.