Coffee grounds are fine to use as a thin mulch around your Euphorbia or Crown of Thorns. You do need to work the grounds into the soil a bit so they won't form a hard crust in the sun that could block water. A thin layer would  be less than half an inch so it won't be a good way to get rid of a lot of coffee grounds. You may want to start a compost pile for your coffee grounds and kitchen waste. Keep growing, Marianne Binetti