There are quite a few opinions on planting bamboo and how to plant it and which way it will grow. The basic rule is that if the ground is level and you plant bamboo it will tend to grow towards water and or towards warm soil. Likely in the northern hemisphere this will mean that bamboo would tend to head south. That's the direction the sunlight will come from anyway and the direction where the soil should be warmer.
On hills though there is another dynamic to consider. The rhizomes of bamboo tend to be relatively shallow 6 inches to 18 inches at the most. This is quite a bit different from trees.... The bottom line is that bamboo tends to grow faster down a bank than up a bank.
Why? As the rhizomes grow down and out they should stay closer to the surface where it's warmer and not as much energy is needed to get culms up above the ground. Trying to grow uphill on the other hand means that the rhizomes are digging deeper into the ground and then up. It takes more energy to get culms up through more ground and so growth on the uphill side should be slower.
At least that's what the popular theory is from what I've been able to see. We currently have a couple of bamboo on a slope experiments going and I'll update in a couple years to let you know which seems to be win out.
I guess the million dollar question is what if you plant it on a slope with the south end being uphill and the north end being down hill.... will it balance out and grow the same amount in each direction.
Sorry but I don't have a good test case of that one.... I'll have to try and find a place to try that out I guess.
