When your field is Unfertilized, rezz your Compost nearby, Click on your field and say Fertilize, your compost will disapear, and your field will change to unseeded

your field is now, unseeded rezz out your Seed package nearby, First click your field then on the pop up click seed, then you click your seed packages, and your seed package will disappear and your field will turn paused

when your field are paused, it means they need either water or tending, sit on your field and on the pop up click water or tending once you have done both acts, that take 1 minute each, the text will turn white and the timing to count down until you can harvest will begin. 

once you have watered and tending your field, the growing time with start counting down and your field looks darker as it has water now. Due to time drift issues it can happen that your field will pause and needs more water or tending before you can harvest

when your field says it's Ready to Harvest all you have to do is sit on it, then on the blue pop up say harvest and you start riding your tractor