Here is the full list of all 50 Viva Piñata (GFWL) achievements worth 1,000 gamerscore. It takes around 40-50 hours to unlock all of the achievements.
Played the game for 50 hours (real time)
Successfully completed 20 Factory requests
Player has healed a Piñata with the Chewnicorn's power
Evolved 8 species
Made 50 species resident
Garden worth 100,000 chocolate coins
One Piñata worth 10,000 chocolate coins
Full bonus growth for 25 plants
Player has reached Level 50
One Piñata worth 5,000 chocolate coins
Player has used the Mallowolf to scare off Ruffians
Player has attained full bonus growth for a plant using the Cocoadile tears
Become Master Romancer for 20 species
Cross romancing a Swanana and a Rashberry
Player has 100,000 chocolate coins
Player has 25,000 chocolate coins
Full bonus growth for 5 plants
Played the game for 10 hours (real time)
Tower of Sour has 6 pieces
Grown 25 plants to maturity
All the Shovel Handle upgrades
Employed a Diggerling
Player has hatched an egg using the Cluckles
Player has been brought a Romance Sweet by a Macaracoon
All the Watering Can upgrades
Made 20 variant Piñatas
Successfully completed 5 Factory requests
Garden size at maximum
Employed a Watchling
Evolved 2 species
Player has distracted Dastardos with the Crowla
Player has made fertilizer with the Taffly
Player has distracted Dastardos with the Sherbat
Become Master Romancer for 5 species
Garden worth 25,000 chocolate coins
Collected produce from a Buzzlegum, Moozipan or Goobaa
All the Shovel Head upgrades
Employed a Weedling
Employed a Gatherling
Named a Helper
Player turned the Beggar into a Trader
Employed a Sprinkling
Tower of Sour has 2 pieces
Garden size increased once
Player has reached Level 10
Made 5 variant Piñatas
Grown 5 plants to maturity
Made 5 species resident
Made a Custom Label
Named a Piñata