If you use the Structures Plus Mod, there's a recent feature added that I see some still struggle with. Hopefully this guide will help you with the S+ Converter structure and turning your regular Plant Species X seeds into the more advanced S+ Plant Species X, which has targeting features including setting which species to shoot if set for tames or wilds.
First, you will need to reach level 36 of your character. You will then have access to the S+ Plant Species X seed engram, which costs 0 engram points to learn and has no prerequisites. You will need this engram in order to convert your seeds at all.
Next, you are going to need an S+ Converter. It's inexpensive to make, is available when you are level 1, costs 0 engram points, and takes up half the space a normal table does. Access the inventory.
Take Seeds from Your Inventory
After you have accessed the inventory, take the Plant Species X seeds from your inventory...
Place Seeds in S+ Converter's Inventory
...and place the seeds in the S+ Converter's inventory. Now you're ready to begin converting.
Convert Seeds to S+ Seeds
There is a button in the middle (highlighted by mouse) that will convert everything that is vanilla inside the S+ Converter's Inventory into it's S+ counterpart (assuming you have learned the S+ counterpart in your engrams). Press this to convert your regular Plant Species X seeds into...
...S+ Plant Species X seeds! You can now remove these seeds from the S+ Converter and plant them in Large Crop Plots to create your fearsome organic turrets.