When using coffee grounds for your plants you should add a cup of coffee grounds per week to the soil.
Mix the used coffee grounds in the soil and not on top of it.
Then water the plant slightly after adding the coffee grounds into the soil.
House plants that like coffee grounds are.
Plants that prefer more acidic soil (such as African violets, Impatiens, Norfolk Island pines, Phalaenopsis orchids, and Dieffenbachia) seem to respond well to a weekly watering with coffee.
Directly applying coffee grounds to indoor plant soil can cause excessive moisture retention, fungal overgrowth and even impair plant growth.
Coffee grounds are a very useful source of nutrients that indoor plants can use effectively, and a very cost effective fertilizer.
If you want to try adding coffee grounds directly to the soil of your houseplants, only add a thin layer of no more than 1/2 inch and then cover the coffee with a layer of mulch about 4 inches thick.
Generally, the ideal way is to sprinkle a few coffee grounds on the soil once every six weeks.
But it can change depending on the time of year and the plant's growth cycle.
If you use prepared coffee to water the plants, use it once every two to three weeks and in limited amounts and sufficient dilution.