Farms?

You need to research to get farms. Without the game open in front of me, I couldn't tell you what, though. Try checking the planetary improvements chain - the one leading to terraforming, or possibly extreme colonization.

Xeno Farm Construction I, II and III.

Yes, except some civilizations, like Yor and Iconians don't get the best farms in the game, just some crappy ones, so they should buy farming from other civilizations.

ok thanks guys i found it now. its in the research tree as you suggested. sorry for the noob question, but i'm still learning this game

Yor farms are awesome.

Thalans do not get farms as far as I can see, but everything is weird about them. Also, while computer does not do this, you can place agents on farms! This is a powerful way to drive down an opponents population either to reduce economic output or make invasion easier. Each planet can be knocked back to farm output of capital(which can not be neutralized). And, since population recovers slowly, spies can move on the devestate the next planet.

While disabling farms can be useful in an economic or influence battle, you are usually better off using spies on morale structures and using Information Warfare when invading. Not to mention the fact that the same spy can be used to attack multiple planets per turn, and that the spy does not need to be left on the planet for a turn to be effective. Damage from a morale spy is instant.