This is another untested variant but I woke up this morning and it popped into my head and I've spent the last thirty minutes turning it over in my skull, trying to think of how it would play out. I'd love some feedback if you give it a shot and I'll try it the next time I play and let everyone know how it turns out!
When it is your turn, and you are planting a bean, you can ask for help! You ask the group for a specific bean-type you need help planting and they have to give you any cards you ask for that they have in their hand (think Go Fish). You can only ask once per turn and you can only ask for help on beans you are planting at that time (whether you are starting a new bean field, or adding to an existing one, doesn't matter). Giving beans starts with the player clockwise to the asking player and continues unless the asking player has maxed out their coinage on the bean field, in which case, nobody has to help any further.
Trades still occur like normal, this is just an added action.
At the end of each players turn, everyone draws until they have 4 cards in hand. I'm aware that this will deplete the draw deck quickly but I think it's necessary so there will always be cards for "helping".
Ok, play-by-play example!
Plants one Coffee Bean from hand into a Coffee Bean field with 2 already there. Plants one Red Bean into an empty field. At this point, Player 1 can use their "ask for help" option on either the common Coffee or the more rare Red Bean. Player 1 asks the group, "Can anyone of my Amish brethren spare some Coffee Beans?" (or just say "Who's got Coffee"). At this point, you go in order starting to the left of Player 1, everyone with Coffee Beans in their hand will have to give them to Player 1 who will immediately plant them. Then Player 1 flips up their two cards from the draw pile. They are a Coffee Bean and a Stink Bean. They choose to forego trading with anyone, plants their Coffee, harvests their Coffee, then plants their Stink alongside their Red. If they hadn't asked for help with their initial planting, they could have asked for help when they chose to plant either the Stink or the Red. They can't ask if anyone has (blank) card, they must choose to do the planting option, THEN ask for help.
Player 1's turn is over. All players draw cards until they have 4 in hand.
Plants one Green Bean and one Stink. Does NOT ask for help. Player 2 cannot ask for help on these beans anymore unless they are adding more beans to it on their turn. Player 2 flips over a Stink and a Cocoa. Opens up to trading, seeing if Player 1 or anyone else wants the Stink. Player 1 decides to trade their Cocoa bean for the Stink, worried that Player 2 is just going to ask for help on the Cocoa anyway and take it for free. Player 2 accepts the trade. Player 1 takes the Stink and plants it in their field (Player 1 cannot ask for "help" while planting because it is not their turn). Player 2 discards the Stink in their field and plants the 2 Cocoa they have. They ask for help on Cocoa. Nobody else has Cocoa so Player 2's turn is over. Everyone draws cards until they have 4 in hand. Since there wasn't much helping or trading, only Player 1 and 2 wind up drawing cards.
Player 3 plants a String Bean and a Green Bean (Player 2 kicks themself for not asking for a Green Bean). Does NOT ask for help. Flips over the top 2 cards and it is 2 String Beans. Player 3 chooses to forego trading and just plant their 2 String Beans. ONLY ONCE on a Players turn can they ask for help and it is ONLY when a Player PLANTS. Because Player 3 has not asked for help yet, they choose to ask now, as they are planting their two new String Beans. All players starting to the left give Player 3 String Beans if they have any. Player 3's turn ends and everyone draws until they have 4 cards in hand.
Possible problems I see are excessive trading. If you always draw 4 cards, you won't be hesitant to make one-sided trades if you think it benefits you greatly. Also, when everyone has more cards in hand, there are a lot more trade options available to the player whose turn it is. It might lead to over analysis. I think any extra analysis time should be balanced out with game length since the decks should be run through much more quickly, but until I try it out with different player counts, I can't be sure. Also, just setting a timer on trades would be good, but I would suggest that in all games of Bohnanza with more than 3 people