If my Math is correct (I feel like a nerd for saying that) it should be a 20 minute growth cycle. That being said, it is all based on luck, so it could take as little as 3/20th of a second, or it could never grow.
Just because someone says "The wiki says that" doesn't mean that the wiki actually says it. Here is -actual- info from the wiki:  Factors such as light level or proximity to lava do not appear to affect the growth rate of Nether Wart, and it does not respond to bone meal.
I watched the video, and while it is very good (as is the Part 1 video), I believe he is incorrect in saying that planting in multiple chunks increases the average rate at which the netherwart will grow. If chunk updates occur as he stated, then there's a logic error in his probability.
He said the game picks 20 blocks from each chunk and checks them for updates. Assuming that it can pick ANY block, and not limit itself to ones that can update, then each block in that chunk has an equal chance to be picked.
So if you have four 8x8 plots of netherwart, it doesn't matter if all four plots are in the same chunk, or if they are in four separate chunks. The odds of each block updating are exactly the same.
Actually, I believe your logic is somewhat off. Since he has four 8x8 plots, his entire farm could fit into a single chunk if he removed the walkways (not advised, soul sand :dry.gif: ). BUT, if it were in a single chunk, then at most 20 plants could be selected for updating per tick. Since his farm spreads equally across four chunks, each PLOT can have at most 20 plants selected, which means his farm in total can have a maximum of 80 plants selected per tick. If your farm contains less than 20 nether wart, you can build it within a single chunk without affecting total growth rate by much, but for larger farms, you do want to spread them out.
Actually, I believe your logic is somewhat off. ...
Sorry for responding late, but I just saw your response. Incoming wall of text that probably no one will read anyway.
You are using the same logic that the video creator is. As I understand how the game works, yours (and his) are actually the flawed logic.
My argument rests on the following assumption:
Each tick, the game picks 20 blocks at random from EVERY possible block in the chunk (32768 total possible blocks).
If that is correct (which I'm pretty sure it is), then that works out to be approximately the 0.061% chance that a single given block will be chosen each tick (I say approximately, because he mentioned that the same block could theoretically be picked twice). Therefore, ANY single block in the game has that same 0.061% chance to be picked each tick. Those odds are the same regardless of which chunk a block is in, and for every block in the game. That alone should be enough to prove that I'm right, but I'll take it a step further, and try to explain the fault in his logic.
His reasoning (and yours) are that, if you have your 16x16 (or 256) netherwart blocks across multiple chunks, you get 4x as many updates in those chunks than you do in a single chunk. While this is of course true, it does NOT mean that your 16x16 farm block get a better chance for updates. This is where the problem is. I'll prove this by calculating the odds that one of your nether wart blocks is picked for a single given "pick" (with 20 "picks" being chosen per tick, and 20 ticks happening each second), for both cases.
If you have an 8x8 set of farm blocks in one chunk, that's 64 total blocks that are the farm in that chunk. The odds of getting an update on one of those 64 blocks is 64/32768, or 0.195%. So if you have four 8x8 plots in 4 separate chunks, then that's 0.195% x 4 (since as he pointed out, each chunk has its own chance), or 0.78%.
However, if you put all 4 of those 8x8 plots into the same chunk, you now have FOUR TIMES as many blocks in that chunk that can be picked. Specifically, you have 16x16, or 256 farm blocks that can be chosen in that single pick. That means you have a 256/32768 chance of getting an update on one of those blocks, which (you guessed it) is 0.78%.
I think that last part is where you and he made the mistake. Yes, if you have your farm across 4 chunks, you get 4 times the number of updates per second than you do in a single chunk, but that is totally and exactly counteracted by the fact that you have 1/4 the number of possible blocks that can be chosen during each tick in each of those 4 chunks. With all four 8x8 plots being in the same chunk, you have 4 times the odds of one of your blocks being chosen for that chunk, which makes the odds exactly the same either way.
... if it were in a single chunk, then at most 20 plants could be selected for updating per tick. Since his farm spreads equally across four chunks, each PLOT can have at most 20 plants selected, which means his farm in total can have a maximum of 80 plants selected per tick. If your farm contains less than 20 nether wart, you can build it within a single chunk without affecting total growth rate by much, but for larger farms, you do want to spread them out.
This is true, but you are neglecting to factor in the probability of actually having all 20 blocks being chosen. When you do that, you find that while it is theoretically possible that during a given tick you could get more possible blocks updated if you spread them out (as in the example you provided), over time the actual number updated will be exactly the same on average.
Note: Slightly edited because I misused "ticks" and "seconds"...
Wow, this makes like the 3rd thread about nether warts. It is actually pretty funny, there are so many urban legends out there. One question I would ask you, how many did you plant? The more you have the better chance you will get them to grow quickly, due to the shear number of them, regardless of the chunk they are in. I will say that our farms do grow better, when we use the old find a block where the x y axis is divisible by 16, run a line of block or whatever off that block in 4 directions making a cross, plant the wart in the four open areas, basically planting it in 4 separate chunks. It really works, but shear numbers work too. If I was in the nether for 20 min, which I have done, I would have a ton of it. Killing pigmen is a good way to pass the time, you could always use the nuggets.