ASTRONEER

To obtain a seed you need to destroy the specific plant by digging it up with your terrain tool (just dig all around the base of until it explodes) but don't be too close to the plant because you will take damage from it or even die!
The plant normally drops a couple of research items you can scan but sometimes will also drop the seed for that plant.

To plant it simply put it on the ground and hold Y over it , the description will change to "Germinating a new plant" and that's it. Seeds can be planted anywhere, on any terrain, surface or underground.

For this achievment I would advise collecting all 7 seeds first and planting them all in one go, rather than planting as you find them and trying to remember which you've done.

The 7 different plants are spread across 5 of the planets but you can actually do this on only 3 planets: Sylva, Vesania OR Novus, Callidor OR Atrox.
Popcoral and Daggeroot I think can be found on any planet, but I'm not 100% sure. They are both plentiful on your home planet Sylva anyway so it's best to just it do it there.

Here's pictures of the plants (a few of them aren't very good but I can't get my screenshots to share properly ) and where to find them. Good luck space farmer!

Popcoral - Any planet, caves (do on Sylva)

Daggeroot - Any planet, caves (do on Sylva)
These come in two sizes, the large ones can drop the seeds.

Bouncevine - Sylva, mountainsides

Lashleaf - Vesania & Novus, surface

Thistlewhip - Vesania & Novus, surface

Spinelily - Callidor & Atrox, surface

Wheezeweed - Callidor & Atrox, surface