Well, I'm not a fan at all of the Blog format, but that's just me...
It's has it's pro's and con's, and some folks prefer it over basic thread type journaling...
As for starting independent threads for each week, it's redundant... Updates, commentary and such can all be done in the Blog itself, it's kinda pointless to have separate threads, or a single thread even, for your grow journal if you're doing a Blog type journaling...
In the Tutorial Section there's a Blog tutorial by Damien if you want to keep on with that format. Personally, if you're new to all this, the Blog system is a bit cumbersome IMO, and you may prefer a simple single thread grow journal instead, and just update things in Posts in that thread...
I'm not sure there's a simple way to reverse engineer a Blog back into a basic Thread type journal?
No worries man, I hope what I said makes sense! I'm of no help for Blogs unfortunately....