recommended zoo merge for multiple objects

Hello, i have about 20 objects, each object is a zoo object, a ticker 
symbol. 

I am using merge.zoo to merge 2 objects successfully and using return 
class to create a data frame.  However it looks like merge.zoo can only 
handle 2 objects.  What's the recommended approach to merge multiple zoo 
objects by the time index into a data frame?

example of 2 objects:

df <- merge.zoo(XLF,SPY,all=TRUE, retclass="data.frame")
where XLF and SPY are zoo objects.