So I was bored yesterday and so I made a list of all the plants including ones that can't and can go in vertical gardens alone and splice suggestions for the ones that can't. This is based assuming you have all plants though. But the can and can't are still listed so you could work out something.
I have put almost all of these together in my game to test also. () are the splice suggestions. I should add that to splice you do have to do it outside of a vertical garden and then once done drag it back in, and the base plant has to be a VG compatible plant.
Fruit, Can (splice suggestion) - Strawberry (Snapdragon = Dragonfruit) / Blackberry (Cherry, could also add strawberry) /Grape (Dragonfruit) /Tomato (Garlic)
Fruit Can'ts - Apple / Pear / Cherry / Coconut / Pomegranate/ Avocado - All Season - (Pear) / Lemon - All Season - (Apple) / Dragonfruit / Pineapple
Veggie & Herb, Can (splice suggestion) - Spinach (Potato) / Green Bean (onion) / Green Peas (Carrots) / Green Peppers ( Taro Root) / Black Beans (Kava) / Sage (Basil = Parsley)
Veggie Can'ts - Potato / Onion / Carrots / Taro Roots / Kava / Plantain tree (Coconut)
Flowers - Can (splice suggestions) - Bluebells (Valerian root) / Daisy (Lily) / Christmas Rose (Crocus) / Holly (Snowdrop) / Begonia (Orchids) / Chrysanthemum (Bird of Paradise(can) = Tulip (Can't)) / Rose (Wolfsbane) / Dahlia (Mandrake) / Bird of paradise
Outdoor retreat plants - Elderberry/ Toxic (Chamomile/Toxic) / Huckleberry/muckle (Fireleaf/poison FL)
ORp can't - Morel mushrooms (False morel mushrooms) These can be spliced together) / Chamomile/toxic / Fireleaf/Poison
All 4 catnip variations do work in VGs I suggest just splicing 2 together so they only use one VG.
these are remaining plants that can't go in the VGs but could either be spliced together or used alone
Money tree (Glow tree (not tested yet) / Forbidden Fruit tree (Emotion fruit tree -This may only produce the specific Emotion fruit used) /
Mushrooms/ Bonsai bush/ UFO plant / Trash Plant / Bizarre Fruit plant / Sixam Mosquito Trap / Plasma fruit tree/ Fang flower (tentacle) tree /
Quill fruit plant / Glow orb plant.