Seeds can be sown on a dirt tile, grass tiles needs to be packed then cultivated. The [[maximum slope]] on which you can sow seeds is 8, where 8 = (highest north-south tile border's slope) + (highest east-west tile border's slope). For example, the slope can be level EW and 8-steep NS. Or 4-steep EW and 4-steep NS, etc. Attempting to sow seeds on a greater slope results in a message "The ground is not flat enough for crops to grow. You need to flatten it first". Farm tiles function the same with a slope 8, flat or anything in between.
The current minimum harvest yield is 2.
Clearing crops that have turned to weeds will return one seed.