@SherryRN, sure thing, I'm glad to have a gardening discussion.
Yeah, the Groups don't seem to work as well as the Clubs, for me, anyway. I haven't tried them since the expansion, tho. The spacing of the plants is important as well, as @iamsweetmystery said. And if the Sims in the Group are NPCs they might not have the right Skills, etc. Your idea about whittling the size of the garden down as much as possible is another key to keeping them flourishing. Some of the plants I don't use so much, I have spliced. With the Patch, tho, splicing is way trickier. The Rare plants really live up to their names. It can take forever for a spliced plant to actually produce them. I don't think that's a bug, but Carl's Guide or someone was talking about the chance being set to a super low number value, so I don't know if they will dial that back a bit, or not.
I kinda doubt cats would hurt the garden. It does sound like your new gardens are working all right, so yeah, that one may just be bugged. I'm not sure why you wouldn't be able to hire a gardener, so puzzling.
Yep, I noticed the yield is way less, too. (If you want to have a pretty good look at the new changes to Gardening, James, The Sim Supply on YT is doing a Seasons Let's Play which is showing a lot of them, if you're into that, haha.) I actually think the devs were going for more realism. They figured since the changes had to be made for Seasons, this was a good time for a total overhaul. It never hurts to express your thoughts, tho.
For me, before the changes, you could make a crazy amount of money on Gardening. I just think they felt maybe that was too easy, and indeed, folks had been saying that. I don't mind it being a bit more challenging. It is a royal pain until my Sims get on their feet, if I'm playing without cheats. But after that, I tend to make too much money, if there is such a thing. :D The florist bouquets do make a crap ton of money if you get good at that. You can even sell them right off the yard sale table with low overhead, and markups as well, if you have City Living or Jungle Adventure.