The artichoke is a thistle-like plant. The primary stalk will produce the largest bud, but it can be quite spectacular when it blooms. The side buds are much smaller and just as tasty. You want to harvest them when they are still 'tight' because as they develop, the choke will mature. That part is not edible. You will want to cut off as much of the stem at the base of the bud because that's edible, too. I would start harvesting on the lowest part of the plant and experiment a little with size to determine when you get the most edible 'yield'.