Some info from the Zollamt:
http://www.ezv.admin.ch/zollinfo_pri...x.html?lang=de
Essentially, importing the plants listed is forbidden. Importing other plants, as long as for personal use only, is allowed. You will probably be charged MWSt., though.
On the right side of the page, click on '18.51 Einfuhr von Pflanzen durch Privat' for a little more info.
A tip:
In the next couple of weeks most garden centers here will have BIG sales - they don't want to have to overwinter stock. I buy many of my plants in the fall, usually at 50% or more off. You might save yourself a trip that way...
ETA: Another thought about buying from too far away... make sure you understand your mini-climate.

I'm just under 800 meters, but I live on the dark side of the Rossberg - given the amount of sun and slightly cooler temps, I've found I need to plant for 'Hohenlage' even though I shouldn't have to at this elevation. I've made a few costly mistakes planting things (fruit trees especially) that just don't thrive here. I've come to rely on the advice of the nice old gentleman at the local Landi, who has since talked me out of several follies. You probably won't have this problem in Volketswil, but just something to think about.