How is crossbreeding Jute and Tantalplant?

[Vidu]

If you bother reading the whole thread you'll see a link to the place that has the most knowledge about gardening, in FFXIV. Follow it and read the crossbreeding section. Then come back and tell me I screwed up.

Thats usually the kind of thing you'd provide an actual link for, instead of giving people directions from the mainpage of a site someone else. So when you refered to a link, I didnt expect you to be refering to someone elses post.
I'm not quite sure why your reacting so passive-aggressive and are getting hung up about the whole link-debacle instead of sticking to the topic you actually wanted to discuss (or asked for advice on). Not that thats not something one is used to from threads like this by now - so I suppose I'm going to save myself the headache from now and ignore them...

2. I was told the onions don't produce seeds on their own, so I use flowerpots to grow them.

No plant can produce seeds on their own, all seed-production requires crossbreeding, aka: at least two plants, planted next to each other in a garden bed.
Thavnair Onions can be used in quite a few crossbreeds, including premium chocobo foods - non of those crosses are all that great, but they're all possible. Using Thavnair Onions to get the Premium Chocobo Food seeds back that you need in your crossbreed to produce Thavnair Onion seeds is definitly an option.