Starting to garden (although I probably shouldn't)

[PirateCat]

My favored strat for onions is:

Krakka Root + Mandrake = Mimett Gourd (might get Onion Prince instead here) - Krakka root seeds have to be bought but the roots themselves usually turn a modest profit on the MB.
Prickly Pineapple + Old World Fig = Glazenut
Mimett Gourd + Glazenut = Thavnairian Onion (might get Apricot or nothing instead at this step)
Thav Onion + Mandrake = Mimett Gourd (might get Onion Prince instead here too.)

There are more reliable crossbreeds at individual steps, but I like this one because it feeds back on itself. (Edit: This is actually very similar to Chameleon's suggestion, though glazenuts are a more valuable byproduct than pearl roselles.) You can get two plantings of Mandrake in the time it takes for the onions to grow.

A couple of tips for maximizing your crossbreeds:
- If you're planting two types of seeds that take a different amount of time to grow, immediately replace the ones that are done. This way all 4 of the new plants will be eligible to crossbreed.
- If you're starting a bed from scratch and one of the seed types is of low value/easy to get (e.g. mandrake, figs) you can plant the whole bed, then rip out the first plant and replant another to make that space crossbreed too.