Schmeetz, did you actually see a drop in rankings after creating a blog? Seems odd. If that happened, there's probably other things going on that need looking at.
I would target the content for the 'jar' related pages towards jars. Perhaps create some internal links with jar-related phrases to those pages too.
Try and build some external links with partial or even exact match anchor text too - but try and keep the link profile looking un-spammy. (It may be worth doing some analysis of competitors to look at their link profiles before embarking on this.)
A blog that's about organic-type things that earns links in a folder vs subdomain? Keep it in a folder, the links will help the overall authority of your site.