Google's Page Rank algorithm is really hard to understand but I agree that with constant updates with high quality content (especially now after Google's recent 'Farmers' update) and related keywords would really help your PR to rise quite well.

Link exchanges should still work pretty well as well, as Google still considers these quite highly when determining a site's page rank. But things may have changed with the recent update.

Anybody have any idea on this?

Easiest one to do is ask friends to link to your website

Better still link to your website with a key word as the anchor text, such as 'growing vegetables' or 'cooking' or whatever your website is about.