Here are a few suggestions:
- Grounds provide generous amounts of phosphorus, potassium, magnesium, and copper
- Apply as a top dressing to nitrogen-loving plants like lettuces, roses, and most perennials
- Add to your compost pile as green material high in nitrogen in balance with brown materials
- Can be used in worm bins
- Caffeinated coffee grounds can be used the garden to create slug barriers: create a 1/2-to-1 inch wall of coffee grounds around the susceptible plant; replenish as necessary
Source: New York Botanical Garden (nybg.org)
Please consult additional resources for more-detailed information.