Lagering in the garage?

My garage stays between 45 and 50 degrees this time of year. I saw a recipe for a doppelbock and I would like to try it. Would it be possible to lager in my garage if the temp stays around 45-50?

Why wouldn't it be? As long as you are confident you can maintain temp control.

I guess that was my worry. Maybe I should check the temp overnight and ensure that it stays within range. How low can I go without harming fermentation?

Use the large red bucket, the one we use at parties to keep sodas on ice. Full it with water and check the temp of the water early in the am and before you go to bed. That'll give you an idea about your temp swings. It could work

In my cellar i have a thermometer that gives me the current temp. as well as the highest and lowest temps from the previous 24hrs. You may want to invest in one of those and keep track of the temp. swings over the course of a year. At which point you can brew according to the seasons. When my fermentation fridge is in use, I can always brew up any style according to my temp. range and throw that batch into my cellar w/out any problems. the temp swings only a degree or two at most in the cellar but I have that room sealed off and insulated so there is no draft.

It sounds like a good place for fermenting lagered. You can always use a swamp cooler style setup (a large tub with water and perhaps some ice, which you then place your fermenters in) to buffer the temperature swings that occur.

The one thing to be aware of though is that while you will ferment most laggers in that temperature range, they still ideally need to be 'lagered', which involves dropping their temps to close to freezing and aging. Ideally you'd have a few days of diacytl rest in there too (higher temps).

See here for a conversation on ideal lagered fermentation schedules.. one thread of many: https://www.homebrewtalk.com/f13/lagering-beer-78842/

Sine the garage is so cold, it would also be a great place for fermenting ales, all you'd need to do is add a brew belt or similar heat source to keep the temps up a bit.