Whats the coldest temp for plants to stay alive indoors?

no it is way to cold.annuals generally will not tolerate temperatures below 55-60 degrees

If it gets below freezing, wrap them in old blankets or towels and they should be okay.

Keep them well watered. Misting them may help, as it raises the humidity (like the orange growers do). Also if the garage is connected to your house, move them as close to the back as you can , away from the door.

60 degree is the min. Temp I keep my house plant hoard. Do wrap the containers to insulate the roots. If you can keep them above freezing, they should be ok. At 33 degree get a heat source going. Heat lamp if you have electric available.

Depends on type of plants: annuals or perennials. If you know what they are (say, a salvia), you can look up the plant's hardiness. That means the lowest temperature it can withstand and still live. Plants also need light even in winter so you would need to mimic the light outdoors for plants stored in a garage. They can go dormant but they're not invincible. Sunset Publications has a garden book that should answer any question you may have. Or visit your local college extension office in person or online. Tons of free resources there! Where I'm at, I utilize the OSU extension office in Redmond, Oregon.