We have been tumbling North Georgia river stones, and most recently the Summerville Agate, in a 20lb barrel from MJR Tumblers. Each stage of tumbling takes about a week, and at the conclusion of each tumbling stage, I have been dumping the grit and the agate and river stone grit into the flower garden. The flowers LOVE IT! The rose bushes are more plentiful than ever before, and deeper colors than they were last year. One small rose bush that was red last year, was almost tie-dyed looking with streaks of white. The red impatiens are now a shade of orange. The mint and parsley plants are overgrowing! While this is not fertilizer, I can only guess the plants appreciate this concentrated mineral content in the otherwise mostly red clay soil. After I do dump the tumbling grit sludge into the garden I dilute it, and that happens naturally because I need to clean the tumbling barrel before the next stage, and also need to rinse thoroughly the stones before starting the next tumbling phase, or polishing phase, so I am hosing down the barrel and stones over the garden too, and that helps dilute the sludge and make it run over more of the garden to be soaked up.
I am sure that the sludge mix from a cabochon workstation would have the similar effect on your outdoors flowering plants. Never dispense of tumbling or cabochon grit down a drain, and no never, dispense of that valuable mineral sludge, but add it to your garden. For any questions about gardening, or rock tumbling, feel free to contact Charles at firstname.lastname@example.org.
Hope this is helpful!