So I deliberately raised my bank alt to 90 and dragged them to Exalted AC so they could literally do nothing but make those new 28-slot bags. While I do not encourage this at all (it's a pretty big time investment for a short-term gain), there might be some of you out there that just don't play every day, but can at least log on to take advantage of the daily Imperial Silk transmute. Now, if all you do is grow cloth, you're very likely getting more cloth per day than you can turn into silk. If you have a few extra motes, you can finish the job and burn that excess cloth with Song of Harmony. So the question is:

"What is the best way to plant crops to maximize my Imperial Silk production?"

As you know already, a maxxed-out farmer can get 16 plant slots per day. A tailor would be interested in planting only Windshear Cactus and Songbells.

-- each day, you can transmute 40 cloth into one Imperial Silk.

-- you can turn 30 motes and 25 cloth into bonus Imperial Silk an infinite number of times (but if all you're doing is farming, this will be at most once/day also).

Let's say x = the number of Cactus, y = the number of Songbell, and t = the number of days (which will not matter -- the best rate is the best rate, regardless of how long you do it).

Since the plants were upgraded, I seem to get about 4 cloth on average per Cactus. Everyone gets one mote per Songbell. Motes give you the Song of Harmony, and that should be taken into consideration first.

Number of motes = t*y

Number of motes needed for one Song of Harmony = 30

Number of Songs of Harmony = ty/30

Number of cloth needed per Song: 25 (5 per bolt, 5 bolts per Song)

Number of cloth needed to transmute all your motes: ty/30*25 = 5ty/6

The total number of cloth, using my average of 4 per cactus, would be 4*x*t. The idea is, once the Songs are done, to have exactly enough left over to transmute one Imperial Silk per day with your daily cooldown, and have none left over. Each transmute takes 8 bolts = 40 cloth, so the number needed is 40t.

Therefore, we have

4xt - 5ty/6 = 40t

and due to the constraints of the farm's plant plots

x + y = 16

In the first line, we see that t is completely irrelevant. Finding the value where both lines intersect gives you y = 4.9655, which we can safely round up to 5 Songbell plants each day. x must therefore be the remaining 11 slots filled with Cactus plants.

EXAMPLE: t = 120

11 cacti per day * 4 cloth/cactus * 120 days = 5,280 cloth

5 motes per day * 120 days = 600 motes = 20 Songs of Harmony

20 Songs takes 500 cloth away, leaving 4,780 cloth left. That's 956 bolts, or 119.5 Imperial Silk transmutes. Not perfect, but we were rounding to y = 5, and missing maybe one day in 120 is not the worst thing in the world.

Five Songbell/day means you're casting Song of Harmony every six days like clockwork.

"What if you are getting more cloth per cactus?"

While my own average is closer to 4, other people have reported getting an average closer to 5. Re-doing all the above math with 5 cloth per cactus gives y = 6.857 Songbell per day. While I might accept that the real average cloth/cactus is over 4, I really doubt the real average is greater than 5, based purely on comments in wowhead and this forum so far, so the real value of y is probably somewhere between these two results.

CONCLUSION

The best way to maximize your farming yield, if your ONLY consideration is maximizing Imperial Silk, is to plant either 5 or 6 Songbell and the rest Windshear Cactus. Based on my own personal observations, I recommend five Songbell to start, and if you find yourself routinely with cloth left over, upgade to six until you run out of bonus cloth.