At Level 10, gardeners get some opportunities that can lead to the prize of 3 Omni Plant seeds. After this, more of the same type of seeds can be bought through the mailbox.
Once the plant is full-grown, Sims can "Feed" it on things from Sim's inventory, or look for the "Check on Diet" interaction. It should then offer a list of valid "foods" that exist in Sim's inventory.
(It is worth not having too much in Sim's inventory at this point).
There's a bug that may not allow you to order Omni seeds from the mailbox; since Late Night came out, it may have been fixed by the patch.
Another bug that might be relevant: you can't complete opportunities at combined rabbit holes.
You can get another omni plant through buydebug, but I don't think there's been a solution to the problem of not being able to order seed.
An Omni plant does not change quality, apart from fruit and vegetables. It stays at the same quality as when you planted it; it takes a perfect plant to produce the same quality that's fed to it
An omniplant seed can be cloned, potentially to perfect quality by sims with high science skill, with the science station, obtained via the Science rabbit-hole.
The quality of the plant doesn't change once it's planted. Whatever the seed quality is, that's what the plant quality will be. Everything else, fruit, books, fish etc, duplicates at its original quality no matter the quality of the Omni plant.
BUT you must have a perfect quality Omni plant in order to get back the same quality produce.
Only sims with the omni plant oppertunity succeeded can work with those plants.
Omni Plants go barren after they have harvested 25 produce
Ideally, fertilize with Perfect Life Fruit.
Sita March 2024