There are 13 Trophies that can be collected.

Bronze

Sowing the seeds of love
Grow your first fruit tree

Blown away
Grow 50% of plants in 'Wind Surfing', 'Kaboom!', 'Blown Away', and 'Handle With Care'

Turn that thing off
Drop a bomb on a musician

Listen to the flower people
Re-bloom some flowers carrying 3 musicians at once

Time to hit the sack
Hit every pollen sack in 'Batteries Not Included', 'Zap!', and 'Into the Machine'

Happy birthday to me
Complete 'Grab Hold', 'Watch Out, They Spit', and 'Hold on Tight' in under 20 minutes

Someone set us up the bomb
Drop a bomb on the second player in a co-op game

Let's clear the air
Clear most of the smog in the smoggy levels

The devil wears produce
Hold a musican, heavy fruit, lantern fruit, and explosive fruit while wearing red horns

Silver

Rainbow collection
Collect all the bonus flowers in the game

I wanna be a rock star
Pick up every musician in the game at least once

A very good year
Collect 17 crystals in the game

Gold

Color your world
Grow all the flowers on every level

http://www.ps3trophies.org/game/the-undergarden/trophies/