The cost of food in the Bay Area keeps climbing. In the last year, grocery prices here have risen by nearly 6 percent on average. That means an average Bay Area household is spending nearly $40 more at the grocery store every month.  People looking for savings know about clipping coupons … buying in bulk … but there’s another option that’s helping make it easier to save on food.  Growing your OWN at-home garden — and here to explain is KQED’s outdoors reporter Sarah Wright.