You will benefit from understanding how to assess a bamboo’s stage of development both in terms of choosing a plant to purchase, and in preparation for planting.  Based on my experience dividing and growing thousands of propagations, I classify container plants into five major stages of development, each with distinctly different needs that affect planting technique and post-transplant performance.  Large, field dug divisions fall into a class of their own because their size affords them an energy storage capacity that makes them nearly bullet-proof if properly dug.  In fact, I have never seen a large division fail that was properly cared for.  Even in the rare event that the culms die back completely, there is so much energy in the rhizome that it will send up new growth eventually.  

New Divisions;  This term refers to plants that have just been removed from containers and divided, or for rhizome propagations in their first season of growth.  In either case, plants in this stage are the most tender and susceptible to plant stress or loss.   A larger root ball will generally sustain the top growth better than divisions with a smaller root ball, and will be quicker to establish.  Divisions with a small root/rhizome ball, and even more so, rhizome propagations, lack the food reserves to grow feeder roots, culms and leaves all at the same time.  Plants will generally utilize energy reserves to produce/replace the food-producing organs first (i.e. new shoots that will branch and leaf out) with new root growth following.  New divisions need optimal conditions to survive this stage, and should never be disturbed or removed from their containers.  Leaves are especially susceptible to desiccation due to the lack of a developed root system, so they should have protection from hot sun, wind, and low humidity.

Stabilized Plants;  I use this term to describe new propagations that are “out of the woods”, and able to sustain healthy foliage, but have very little new root growth.  If lifted from the pot, the soil or potting mix will fall away from the root ball exposing tender white tips of new root growth. Depending on the species, propagation technique and size, environment and time of year, it may take 1-6 months for a new division to become stabilized.  Stabilized propagations can be planted out, but it is probably safer to let them remain in the pot until roots can develop further.  If it is necessary to plant a stabilized division, then take care not to disturb the root ball any more than is necessary.  Be gentle!

Well Rooted Plants;  I use this term to describe plants that have a root system that has just grown out to the edges of its container.  If removed from the pot carefully, root development is sufficient to hold the soil or potting mix in the shape of the container, but can easily be removed from the root ball.  Well rooted plants can be placed directly into the planting hole without any special treatment.

Fully Rooted Plants;  These plants have fully developed roots crowding the edges and bottom of the container, reminding me of cooked spaghetti noodles.  The roots are healthy, pliable, and white in color.  Young rhizome may also be starting to wrap around the inside of the container.  Fully rooted plants will benefit from root pruning and separation at the time of planting.  I use the dull “hook” side of my bypass pruners to tease apart the roots all along the sides and the bottom of the container.  I also use the pruners to trim off any broken or tangled roots. Rhizomes can be teased away from the root ball and stretched out in the planting hole, or trimmed to a node past a point of breakage.

Root Bound Plants;  At this stage, aging and dead rhizomes are wrapped around the container perimeter, and old roots crowd the bottom and sides of the container.  Together they form a dry, woody shell in the shape of the container.  Fibrous roots in the interior of the container also age and die, becoming a congested, twiggy mass.  With little room for new root growth, plants soon exhibit a marked decline in vigor.  However, root bound bamboos can survive and produce new shoots (thought stunted and less vigorous) for years, even in neglected containers.  If watered and fertilized, they can look presentable, even healthy if the old, stressed culms are removed regularly.  When planting root bound bamboos, I remove the whole outer layer (dead) of woody root and rhizome, which stimulates new growth and speeds the establishment of the planting.  For smaller plants, a pair of pruners or loppers will usually do the trick.  For larger plants I use a sawzall with a wood pruning blade to slice off the woody material.   Even without pruning, a root bound bamboo will survive and eventually thrive once planted out.