I think box directions should be fine. They say place a tab for every 4-6 inches of gravel radius around the plants and use every 3-4 months. What I'm doing is splitting a tab in half. (using a flat-blade screwdriver and a little whack on a hard surface. These things are tough!)....and then sticking with the shorter 3 month interval. I'm sure others will have other amendments to the directions. I'm sure the key here is to NOT overdo it.
Andy
Andy