Mother[']s Day:To Optimize With or Without the Apostrophe

I was just looking over last year's search stats (2008) for a floral website that I run that ranked in the top 5 results (in Google) for all of the following keywords. Of interest in that regard, is the search volume difference between the use or non use of the apostrophe.

These stats represent the 5 days leading up to Mother's Day. 

Keyword	Visits	% visits
mothers day flowers	2,366	44.69%
mother's day flowers	1,585	29.94%
flowers for mothers day	427	8.07%
flowers for mother's day	158	2.98%
flowers mothers day	84	1.59%