How do I stop my planets from defecting?

1.)Keep morale up. Use the Propaganda button liberally.

2.)Keep at least one ship in orbit. This does help.

3.)Build starbases with Cultural Influence boosters.

If these don't work, destroy the colony! BWAHAHAHAHAHAHA!!! Umm..excuse me. A bit of evil popping out.

Ok, I"ll try that. I did notice that some of my planets had low morale, so I tried switching to morale-boosting productions, such as entertainment networks and virtual reality centers. I guess in this case it was too little, too late.

When possible, slip in morale productions. I generally always build the entertainment network, since it costs so little to maintain and gives you so much bang for the buck. I think the consensus around here is the Virtual Reality Center is too expensive to build.

Hope this helps, and I know there are many here who have more suggestions. I'm still fairly new myself.

You can add starbases with cultural modules in the relevant sector in order to gain influence there. Add enough starbases and you'll be flipping the aliens to you!

Then there is the ultimate influence equalizer: war. Find what alien is your planet stealer, take some systems away from him while being especially vigilant in destroying influence resource starbases (as well as the standard trashing of military, economy, and morale resource starbases). Your base influence is determined by adding all of your systems together and modifying it at various levels with tech, resources, social projects, culture starbases and so forth. Reducing the size of your rival's empire while increasing the size of your empire helps alleviate the base influence problem at its source. Oh, and be sure that you not only destroy the resource starbases in the war, but claim them for yourself. After a healthy little war that bags the problem starbases and snags a planet or three, force concessions out of the poor alien at the peace talks. If all goes well, the influence advantage over you will be eliminated and you will gain an overall influence that can effect every alien on the map with your greatness, instead of them walking all over you.

If the I-League is active, any planet suffering from chronic low morale will flip over - due to unhappiness. The unhappy face is usually present.

If the plannet is flipping to another major race, influence is the key factor. If your influence in the sector is less than foreign influence you are in danger of losing the planet. You can prevent/slowdown flipping by getting more influence in the sectory, mining influence resources, raising cultural resistence, or raising morale. Only having more influence in the sector will definitely prevent cultural flipping.

You can slowdown cultural flipping by declaring war on the cultural aggressor. By capturing the closest planets and destroying closest starbases, you can alleviate the cultural problem.