Under the current agriculture system, a crop cannot be planted if it would not be able to grow under the current conditions. I suggest that the game display a text message to this effect (such as the "you can only sleep at night" message for beds) when a crop cannot be placed. For example, attempting to plant at night or without enough sunlight will display the message "This crop requires sunlight to grow" and planting a crop in to a too dry block displays the message "This crop requires hydrated soil to grow."
