This is an old thread back in Feb but to answer it use the cultivator on the planted seeds as it will restore it to ground again.
The cultivator is a farming tool for tilling soil, planting seeds, and restoring damaged environments.

On a similar subject

How long do trees take to grow?

I generally avoid this problem. To seed in a row, I plant 1 seed and then back up as I plant the others . Takes very little skill to get them fairly evenly spaced and in a straight line.

Plants want roughly 1 meter clearance on all sides to be healthy. It is possible to squeeze them in closer, but the lost production due to crowded plants isn't worth the bother. I have found it worthwhile to start a few rows that are healthy, then sidestep while planting to get a straight line. You can experiment with different move speeds and planting frequency to get the rhythm right.

Nice necroposting..

Originally posted by FTZ35:

Nice necroposting..

Credit where credit is due... at least the first reply shows they searched the discussions first.

ya planting is kinda annoying, cuz u dont see the range of other plants and were is space tp place them so u loose some stuff... while planting or u build a struckture around the plants in sections so u make shure everything works.. i would favor a range placement were i can see, is a free place good for the new seed..

Cannot recover already planted seeds as far as I am aware. Like said before, sometimes they wait until the plant next to them gets picked and they start to grow. If you are concerned with aesthetics then try a gentler hand on the 'ol cultivator.

You can only destroy them, pretty much any attack.
Note that "needs more room to grow" doesn't mean it will definitely die, sometimes it just slows down growth.

Yeah, destroying them (a pickaxe hit, or a spear toss for precision works for me) is the only vanilla solution to removing them. If you just planted some too close, you can try leaving them there, I had one lucky instance of one plant getting ready to harvest before the one too close died and once removed the first, the second turned out healthy again.

I prefer to kick them (middle click). You cannot recover the seeds of your crowded plants, so your only choices are to destroy or ignore them.

Was also wondering :)

You want them back or just to get rid of? Getting them back is not an option that i know of, but if you use the axe to chop it and will disappear after a few seconds.

punch them