For those still having trouble with them.

Unicorn Help from Sim UniverseBless and curse of plants (flora) (green / yellow horn)

This option can be very helpful if your Sims have a hobby gardener in the defense. With blessing of plants, the plants will go to the next phase of growth. Dead plants (such as the death flower) can be brought back to life. Mature plants have fruits.
When the curse of plants, the plants will just die.

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Source: Sims Nieuws