Super simple idea that would make gardener now still totally worthwhile.
Make it so most, if not all current crops can be planted in a gardening pot.
Potential changes could be that the plant grows faster but has a slightly, slightly smaller chance of getting a quality boost or something. OR grow slower but have a higher chance and yield more than a ground-planted variant. So many options here.
This could also be a fun opportunity to change the mechanics of some crops a little bit too. It stands to reason that if you are growing something in a small pot that you are babying it more and taking better care of it, giving it high quality soil and water. Perhaps the idea of creating cultivars could sneak in to play here.
Example, when a carrot >q100 is grown in a pot it has a .01% chance of one of its harvested carrots being harvested as a "white carrot" variant. Perhaps this "white carrot" variant has absolutely zero use beyond mulch/animal feed but you can continue to grow them in garden pots and raise the q, and a "white carrot" >q150 has a .01% chance of having one of its harvested carrots being harvested as a Daikon or a Parsnip. This would be a totally new vegetable with actual recipes and new feps that can continue to be planted like normal.
Another super simple idea would be just adding new parts to existing vegetables. Maybe an onion grown in a pot can be harvested as an onion, or if you leave it a bit longer you get a new option like "trim" and you just get "green onion stalk" a new onion variant or spice with new feps and shit, and the onion will remain in the pot at the same quality and need more water.
EDIT: forgot to mention, maybe these new harvesting and cultivating abilities are obviously unlocked in the gardener tree.