I’m making items based off of the crop plots, how do I:
Remove the need for fertilizer and water (I can turn it down to near nothing, which I will do if necessary).
Make the plants that spawn non-harvestable, instant growing, and last a full week.
Change the meshes/plant types that can spawn.
Thanks for your help!
These parameters are defined in seed blueprints, not the crop plot. Look for the “crops” category at the very bottom. It has overall fertilizer/water consumption rates and stages of growing with their own fertilizer requirements and mesh definitions.
Setting a single growth stage will probably give you the wanted instant-grown plant, and setting no produce (don’t remember the field name) will prevent any fruit from appearing. However, you will still need 1 inventory slot to insert the seeds.
What the crop plot settings control is water capacity and the range within which water taps will irrigate them.
Lovely! Perfect answer. 
Follow up question: can I specify an existing seed to behave classically in the crop plots, and in a different way in my objects, or would you suggest I simply just make new seed types?
Thanks for the help!
I don’t think you can make it behave in various ways. There is just one universal crop setting per seed, and it doesn’t seem to reference the crop plot at all.
The restrictions for plants, for example, are defined simply via crop plot inventory, disallowing you to put veggie seeds into small plots or spitting plants on any but large plots.