When looking at the Radish charts below you can see that crop 7 (planted on the farm) has been watered twice a day. It took 4 days to grow exactly as displayed on the seed bag, whilst crop 14 (planted on the public field) which has also been watered twice only took 3 days to grow.
Crop 8 (planted at the public field) has only been watered once each day, but due to the public field bonus it only took 4 days to grow. Whilst crop 1 (planted on the farm) took all 5 days to grow.


I also looked at Broccoli since it takes longer to grow. When looking at the charts below you'll notice that crop 13 (planted on the farm) actually took 8 days to grow, rather than the 9 displayed on the seed bag. Crop 26 however took 7 days to grow which makes sense because it took the bonus from the public field along with the double watering. Crop 1 took 11 days and crop 14 took 9 days to grow, as displayed correctly on the seed bag.


I hoped to discover a percentage of growth improvement depending on the amount of water you had given but I'm not thát good at mathematics. It's however useful to know (and have proven) that, when a crop gets both the bonus from watering twice and the public field, it will grow twice as fast as the difference between the [blank] to [blank] days displayed at the seed bag.