When I set up planting beds I lay out wooden floor tiles and then pick up some so that my planting beds are 4 wide by X long. That gives me a nice frame to work in (much like using a string and stakes in a real garden).

To be healthy requires about .7 meters of space per plant. If you plant side to side or plant while walking backwards you don't get proper plant spacing and can lose some plants to lacking space. If you plant walking forward this does not happen. The plant stays red until there is enough space between it and the previous plant. If you click too soon you get the need cultivated soil error message. 4 floor tiles worth of space gets you 5 rows of plants if you want to be perfect with pant health (you can go with 4 rows in that space to make certain).

What might cause uneven rows is using the left mouse button to plant since bumping the mouse to one side or the other can change your perspective and therefore the placement of your plants. If you are OCD and want perfect rows with perfect plant spacing go to options and rebind attack to a key instead of the left mouse button. Use the mouse to line up your row with the edge of the wooden floor/fence/previous row/what ever then let go the mouse and use the "W" key to move perfectly forward and the newly bound key to plant when the plant turns green with out risk of bumping the mouse. Once you have perfectly planted rows you can rebind attack to the left mouse button.

https://steamcommunity.com/sharedfiles/filedetails/?id=2857321032

My main base has 3, 4 x 25 tile beds. Each bed will hold 175 plants and it takes me about 15 minutes to plant all 3 beds. I usually feed my boars and wolves before I start planting as they reproduce while I'm planting and the piggies and wolf cubs will mature later no matter where I happen to be.