With the latest patch, now it's possible to make the grass grow again !
There is a new action under Farming, "Pour water". You just need to have water in your inventory. Right-click a tile which is loosened soil, select "Pour water", and the grass, flowers and ferns will magically and instantaneously appear again !
Thank you devs for this, it's really awesome !
P.S. Devs have confirmed it's not related to crops, it's really only for grass :
http://steamcommunity.com/app/290080/di ... 1036576007