Abstract: A form for shaping a culm of a plant, such as bamboo, is provided. Embodiments of the form can comprise two interlocking corner pieces that can force the culm to grow in a square (or other multisided) shape. The interlocking corner pieces can be frictionally engaged, and the magnitude of the frictional force can be adjusted and optimized. The size of the form can then be automatically expandable, depending on the amount of friction placed on the interlocking corner pieces. In described embodiments, an optimized magnitude of frictional force can allow the form to expand if the culm is too large for the form (such as, for example, if the width of the form is set to be less than the actual width of the culm), while at the same time resisting such expansion enough to shape the culm as desired.