Co-op farming is newly introduced feature by zynga . Players whp reached level 20 and above can begin a task. When ever a task is started the player can posts to recruit neighbor to participate, players can participate completeing tasks at level 1.Here there are 3 levels of achievement for each task, Bronze, Silver, and Gold. Each level has a constraint on time to complete, the faster one is completed the higher the rewards. Here we can find ribbons which can only be achieved with co-op farming, see the ribbons table for more details. When the Gold level is completed you also receive a limited edition gift.

The new feature co-op farming has tasks, achievements, and ribbons. There is a new table for the co-op farming and the ribbons have been added.

You start with a 12x12 land size with one field each of eggplant and strawberry ready for harvest. One field each of eggplant and strawberry at 50% and 57% ready, and two plowed fields. You may participate in completing tasks for your neighbors in co-op farming achievements.
You have the following purchasing and gifting abilities at Level 1:

Seeds:
Strawberry, Eggplant, Wheat, Soybean, and Peanut Seeds.
Trees:
Cherry, Apple, Orange, and Acai Trees.
Animals:
Cow
Buildings:
Red Barn
Decorations:
Whitewash Fence, White, Pink, Red, Orange, Green, Blue, Violet, Gray, and Jet Black Hay Bales, FarmVille and Zynga Flags.
Gifts:
Send Apple, Cherry, Durian, and Gulmohar Trees; Goose and Cow; Fancy Topiary; Fuschia and Pink Greenery; Kensington Bench; Mystery Gift; Picket, Whitewash, and Wood Picket Fences; Sunflower in Bucket.

Most of the Farm Cash items are available for purchase at level 1, as you move up in levels more items are unlocked for purchase and gifting.