Question: how big are cactus roots?
Answer: Roots. Many cacti have roots that spread out widely, but only penetrate a short distance into the soil. In one case, a young saguaro only 12 cm (4.7 in) tall had a root system with a diameter of 2 m (7 ft), but no more than 10 cm (4 in) deep. Cacti can also form new roots quickly when rain falls after a drought.