Ah! I thought it had something to do with holidays... Also, on the US graph there's also a discernable a mini-spike right on or just before the first quarter.

Ah! I thought it had something to do with holidays... Also, on the US graph there's also a discernable a mini-spike right on or just before the first quarter. I can't come up with an answer for that. One guess is that people are looking into planting flowers for the springtime around then.