Myself, I hold my mouse as still as possible, walk sideways, spacing seeds by eye and timing. At the end of the row, a couple taps to back up and then go up the next row the opposite way planting 'in line' with the previous row.

It's not too bad. Of course, if I could plant seeds like grass, it would be awesome.

Harvesting annoys me though. I wish the cultivator would pull anything in it's AoE out of the ground for pick up. If not the Cultivator, then perhaps a new tool, but it makes more sense to me to just add that function to the existing farming tool.