Cleistocactus colademononis grows pendulous, branching at the base, and grows up to 2.5 meters in length. The diameter of the light green body is from 3 to 7 centimeters. The lower 14 to 20 ribs are occupied by areolas at 3 to 6 millimeter intervals. From them arise (0 to) 4 to 8 thorns more or less turned downwards, similar to yellowish bristles and 20 to 50 thorns similar to hairs, white, 4 to 8 (up to 12) centimeters long . The hair-like thorns grow back.

The flower is zygomorphic, 7 to 8 centimeters long and bright red in color. It appears almost horizontally on the areola. The fruit is more or less spherical, reddish and has a diameter of 8 to 12 millimeters. After drying, it is torn lengthwise. The seeds are black, 1.1 to 1.4 millimeters long and slightly curved. They germinate easily.