Well-intentioned DIY bloggers offer many creative suggestions for how to recycle used coffee grounds, but we checked with the experts, and the following three ideas don't hold water:
Cultivate blue hydrangeas Truth: Acidic soil allows hydrangeas to absorb more aluminum from the soil, which turns their petals blue. Truth: Coffee grounds are highly acidic. Lie: Adding coffee grounds to your soil will make hydrangeas turn blue. "The problem is, coffee grounds' impact on the soil is very short term," says Myers. "It's very difficult to change soil's pH."
Unclog drains Plumbers agree, nothing will clog a drain faster than the combination of coffee grounds and cooking grease. Even if you flush them down the drain at different times, cooled grease catches on the inside of pipes, lying in wait to make a gluey mess.
Use as roach bait You may have heard that roaches are attracted to the smell of coffee grounds, which makes them useful as bait for homemade traps. Orkin entomologist Ron Harrison says the cockroaches would certainly be trapped by the tape, but they’re not particularly attracted to coffee grounds.