You don't need to be the bus driver to know what makes the wheels go around. I'm sure a good number of growers know a lot about how milkweed will respond to pruning even if all they use in their predictions is their experience working with other plants. While there are a few plants that don't respond to pruning in ways we might expect (Norfolk Island Pine, for one) most plants (and I mean at least 99%) respond just as you would expect them to respond when you alter the balance of growth regulators that determine whether the plant concentrates it's growing efforts in additive or multiplicative growth. Your plant, is naturally apically dominant, so it wants to grow additively, and it is. To change it's habit temporarily to multiplicative (more branches instead of longer branches) you need to remove the source of the growth regulator (auxin) that is inhibiting multiplicative (lateral) growth. The most significant source of auxin is found in apical meristems (growing branch tips). Dr Carl Whitcomb often notes there is a "4-inch rule" that applies to pruning containerized plants. He suggests that removing an apical meristem affects the growth of other nodes for a distance of about 4" proximal to the cut. So - removing a branch tip affects the growth on that branch for approximately 4" behind that cut. I have a lit of experience doing hard pruning of plants, in which I remove up to 100% of the green growth on a given branch (or even the entire tree). I can attest that harder pruning of one branch can affect the back-budding response of the entire plant. IOW - the harder you prune, the more latent buds you can expect to be activated. Also, as noted above, WHEN you prune and how much stored energy the plant has at the time you prune impacts back-budding response. Healthy trees with lots of stored energy will be much more cooperative when it comes to back-budding than plants that are just getting by. In the picture you posted, I would have either pruned just above the first pair of leaves, then pruned again after the 2 branches that grew from buds in the leaf axils had 3 pairs of leaves - I'd have pruned the secondary branches back to 1 pair of leaves, too. If I had originally pruned back to 2 sets of leaves, I would wait for a week to ensure bud activation in all 4 leaf axils and would remove the top 2 leaves if it didn't occur in the bottom set. You really have a lot of time to pinch most plants. I pinch hardy hibiscus at least 3 times. It gives me shorter, sturdier plants and lots more blooms. In fact, I pinch a LOT of plants very regularly to force them to grow in ways I want them to grow, instead of allowing them to do their own thing. Some plants I've pinched with the specific intent of altering their growth habit: Al

In following a claim that VC contained the growth hormone Auxin, I found a link you may find interesting/useful. Scroll down to HORMONAL INFLUENCES. Haven't seen similar claims about regular compost. Actually, I found the entire document instructive re: distinct cell types in all plant material. [SIGH...so much to learn, so little brain power] Here is a link that might be useful: NATURAL Growth hormones in Vermicompost?

2 feet might be deep enough to contain it, and your retainer needs to be above ground level so you can observe any rhizomes that try to escape on the surface. Once it does fill in it will continue to put up new culms, and yes the old ones die off as the plant matures. Water depends on what the weather has been doing, but certainly if it hasn't rained a nice deep watering weekly works nicely, or just water when your yard gets watered. If not maintained and properly contained it will become a nightmare to you and your neighbors! I tried to include a link to their site, but google bamboo barrier and then check out the Lewis Bamboo site for some more containment info.

I'm not sure this answers your question directly, but tree growth is all about using available energy for adding bio-mass in the form of branch extension and foliage until around the summer solstice. At that time, branch extension slows dramatically as the tree sets buds and begins to store energy for dormancy in roots and cambial tissues. In addition, root restriction in containers causes varying degrees of reduction in branch extension. This is one of the techniques that bonsai practitioners rely on to keep internodes short and trees compact. A good treeman can look at a containerized tree & tell you exactly the year your tree was last repotted. The bud scale scars show a history of recent years and the much wider distance between leaf bundle scars will tell what how many years ago the repot occurred. The longer the tree goes w/o a repot, the more compressed the leaf bundle scars will be, but they will really stretch out following a repot. Trees grown in situ follow a more regular growth pattern. Al