I have access to coffee grounds, and I'd love to use them in my compost pile. Are they too acidic? What about the grounds being toxic to certain plants?
Researchers have found that coffee grounds are beneficial to plants. Cindy Wise, the compost specialist at Oregon State University Extension is a big believer. She says, "coffee grounds by volume have about two percent nitrogen, and are a safe substitute from the pathogens concerns when using animal manure in a compost pile.
The grounds provide all the necessary bacteria needed to turn organic matter into compost.
Contrary to popular belief, she also has found that coffee grounds are not acidic. Instead, the grounds are closer to pH neutral, between 6.5 and 6.8 after brewing. The acidity in the beans is primarily water-soluble, so it leaches into the coffee we drink.
Coffee grounds can be used in several different ways in a garden. Besides a compost pile, they're used as a soil amendment and mixed into the native soil when planting new ornamentals. When mixed with other materials, they're used as a mulch and spread around landscape plants and in open areas.
Not composted or raw coffee grounds will use up the available nitrogen when encouraging the growth of microbes in the soil. Hence, it's important to feed plants often with an All-Purpose fertilizer or similar product while the microbes are breaking down the grounds. This will prevent the plants from turning yellow from a nitrogen deficiency.
Coffee grounds can be added to both active and passive compost piles. In an active compost pile that is often turned and creates heat, layering one part dry leaves to one part fresh grass clippings to one part coffee grounds, by volume is recommended. When turned weekly, the compost will be ready in three to six months.
You can add coffee grounds, to an existing pile but be sure to add an equal amount of high carbon (brown) source, such as dry leaves, straw, or strip of paper, to balance right. We're looking a fifty/fifty ratio between the green and brown components.
Oregon State University Extension has had some issues with poor seed germination when using in uncomposted coffee grounds in the seed trays or flats so it may be wise to avoid them in this occurrence.
It would be best if you made prior arrangements with a neighborhood coffee shop to collect grounds. I'd provide them with a clean five-gallon bucket with a lid. Label the bucket with your name and telephone number on the bucket and lid, and then pick it up at the shop's convenience. Coffee grounds may be stored in large plastic bags for future use, but only if they're to use in an active compost pile. They may develop a mold that disappears in the composting process. And yes, the paper coffee filters may be composted with the grounds.
NOTE: Besides your garden, coffee grounds can help absorb and eliminate odors from your refrigerator, gym bag, or smelly shoes. You can place a bowl of coffee grounds in your fridge or freezer to neutralize odors from spoiled or fragrant foods. Using them as a hand scrub can also help remove lingering smells from onion or garlic.