There are a few different Opportunity cards regarding your Singular Plant: one of them is The Noted Orchid-Grower Consults, which gives you a chance to improve your plant (and a chance the grower is entirely wrong, and gives you incorrect advice). As you've noticed, it's random. But there are two other Opportunity cards that can help: Your House-plant, which allows you to improve your shrubbery by spending Moon-Pearls, and Your Green Companion, which allows you to grow your green thing by spending Jade. (You can also sing or talk to your plant on those two cards, which has a small chance of improving things and no chance of damaging the plant, but it's chancy.)
If the Random Number God hates you, just discard all of the Noted Orchid-Grower cards, and spend money on the other two. If you're cheap, then discard the Noted Orchid-Grower cards and sing or talk to your plant with the other two; it will be slower, but much cheaper.