"X, Y, and Z increase neurogenesis"
The unifying mechanism of herbs, foods, and practices like exercise that promote neurogenesis is that they help increase the three main requirements of neurons
Energetic substrate, oxygen, and stimulation
A huge amount of herbs that increase BDNF do so via the latter two mechanisms, they stimulate neurons and increase blood flow
Bacopa, gotu kola, and gingko biloba are good examples, they stimulated neurons by raising acetylcholine/serotonin/dopamine and increase circulation via mechanisms like PDE inhibition
While the brain's preferred fuel is glucose, hyperglycemia inactivates neurogenesis
Many herbs and foods, like ginseng and cacao, promote insulin sensitivity and glucose uptake and utilization by the brain
Alternative fuels that signal energy depletion also drive neurogenesis in a hormetic fashion, specifically ketones and lactate
This is why high cognitive activity and exercise are so beneficial, they are extremely stimulating to neurons, enhance stimulation, and create a shift from glucose -> lactate/ketones