My val grows annoyingly fast. I recently trimmed it to 15cm below the waterline. The next day it was at the waterline. So I trimmed it again to the same level and yup.....overnight, 15cm growth (6 inches for you american peeps)
I trim about 8 inches off every 3 days. It it loving my tank now that I have co2 and the EI happening in there. Thats my big mondo stuff though. The thinner val isn't growing much at all.
I have never taken a plant out to measure it though. I'm sure mine will be at least that long after my 2 week vacation.