Sadly this table is unreliable, because grass grows at different rates according to temperature and rainfall,
Also, this thread is meant mostly to be a collection of ideas, knowledge, and constructions, more than grand historical dwarves. Like, a how-to on breaching aquifers, setting up a mist generator, or a GCS web farm. Not to mention, of course, the usual weaponized traps like drowning chambers, obsidian Gatling gun, and dodge-me traps. In other words, more construction, less instances, although uncommon knowledge is still highly valued. Such as, how to nullify water pressure with diagonal walls and strip prisoners of their equipment.