A bamboo plant (Poaceae) in a container is ready for repotting when its roots outgrow the pot. Bamboo is a vigorous plant, and many kinds of bamboo are invasive. Growing a bamboo in a container, however, prevents it from spreading and makes taking a non-hardy bamboo indoors during frosty weather simple. Some bamboo varieties grow well indoors year-round. Repotting a bamboo requires replanting it in a slightly larger pot than its current pot.
Selecting a Container
A bamboo plant grows best in a squat container -- one that is wider than it is deep and slightly wider than the plant's root ball. Many kinds of bamboo spread through shoots that grow sideways at or just below the soil surface, and wide, shallow pots provide room for their shoots to grow. Another advantage of squat containers is that they are more stable than pots that are taller than they are wide.
Select a container that is 4 inches wider than the root ball of the bamboo so that all sides of the plant will have 2 inches of growing room. An unglazed clay pot provides the airy conditions in which bamboo roots thrive, but that kind of pot can be heavy, which is a consideration if you plan to move the container. A plastic pot is lighter but retains more moisture around its plant's roots than a clay pot does, and moisture encourages root rot. If the bamboo will stay outdoors in freezing weather, then select a frostproof container.
Transplanting the Bamboo
A bamboo plant usually needs a new pot every three to five years, when little or no soil is between its roots and the wall of its pot. The roots also may circle the pot and grow through the drainage holes. Other signs that a bamboo needs a larger pot are pale-green leaves and poor growth.
You can repot bamboo any time of year. If, though, you repot in spring or summer, when the plant is growing, don't disturb its roots.
Spread a layer of freely draining potting soil in the base of the bamboo's new pot, which is the correct size for the plant and has bottom drainage holes. Make the potting soil deep enough so that the base of the bamboo stems will be 1 inch below the rim of the new pot.
Remove the bamboo from its old pot, and place it in the center of the new pot. Ensure that 1 inch of space is between the base of the plant's stems and the rim of the pot. Adjust the amount of potting soil in the new pot as needed until the bamboo is at that correct depth.
Fill the gaps between the roots and the pot's walls with potting soil. Firm the soil gently with your fingertips.
Pour water over the potting soil surface until it flows through the pot's drainage holes.
Wipe pruning shears' blades with rubbing alcohol, and use the shears to prune withered, diseased and weak bamboo stems, cutting them back to the soil surface. Wipe the pruning shear blades with rubbing alcohol after each cut, preventing the spread of plant diseases. Discard the removed plant debris.
Wait until no more water drips from the pot's drainage holes. Put the drained pot on a drip tray.
Selecting Bamboo for Containers
Tropical bamboo varieties that thrive in warm, partially shaded conditions grows well in pots indoors. Many of them also do well outdoors in the U.S. Department of Agriculture plant hardiness zones in which they grow as perennial plants.
Dwarf fern-leaf bamboo (Pleioblastus pygmaeus) grows 1 to 1 1/2 feet tall and 1 1/2 to 2 1/2 feet wide. It features green stems the thickness of a pencil and purple leaf nodes; nodes are raised bumps on the stems and produce leaves. The leaves are bright green, palm-shaped with serrated edges and about 5 inches long. Dwarf fern-leaf bamboo is a perennial in USDA zones 5 through 10. It requires partial or full shade.
Arrow bamboo (Pseudosasa japonica) grows 12 to 16 feet tall and 12 to 25 feet wide when planted in the ground, but growing it in a pot restricts its size. It can become invasive when planted in the ground, and planting it in a pot prevents that problem. Perennial in USDA zones 6 through 9, arrow bamboo offers dense, dark-green, tapered leaves 5 to 13 inches long and woody, hollow stems. It needs full-sun exposure or partial shade.