When it comes to coffee grounds in the compost, how much is too much? Ask an expert
Gardening season is drawing to a close, but you might still have questions. For answers, see Ask an Expert, an online question-and-answer tool from the Oregon State University Extension Service. OSU extension teachers and master gardeners answer questions within two working days, usually less. To ask a question, just go to the OSU extension website, enter it and indicate the county where you live. Here are some questions asked by other gardeners. What is your?
Q (1 of 2): I was wondering if we could have too much coffee grounds in a compost heap?
I have a three-bin system and I take so many leaves from my neighbor’s garden each fall (about 30 bags of yards). This year, to make sure I have a better balance, I get a 5 gallon bucket of coffee grounds from a local coffee shop every week and add it to each bin in turn so that every three weeks , each section will get the patterns in addition to my kitchen scraps.
I was wondering if the overall pH of my compost would be relatively balanced if I mixed the soil with this huge bounty of leaves or should I go back to the soil? – Multnomah County
A: Interestingly, when a compost pile is made up mostly of plant matter (leaves, food scraps, coffee grounds) it starts out at a low pH and reaches around neutral. Low pH because the decomposition of plant material results in the release of organic acids – initially.
When a compost pile is made up mostly of animal carcasses, manure, and blood meal, it starts off at a high pH and drops roughly neutral. High pH because the easily released nitrogen can be in the form of ammonia – initially.
So the idea of coffee is OK, but the coffee has a fairly low nitrogen content, maybe 2-3% at best. In your situation, I would consider going to the grocery store and buying a 40 pound bag of alfalfa pellets. I would sprinkle the pellets every 3 to 5 inches deep into the pile of leaves. The decomposition of alfalfa will bring in nitrogen and really make the bacteria work in the heaps. Better yet, if you could find a handful of red wiggler worms for each of the bins. One spring I found out I had 50 gallons of worm droppings! – Linda Brewer, OSU Extension Floor Specialist
Q: (2 of 2) I don’t think I know what the nitrogen content range is for the leaves. Do you have this information readily available? 🙂
Also, my bins are full of worms, they are small and red, but I don’t know if these are the official red wrigglers. Do you think they serve a similar service and could replace alfalfa pellets? Or do worms and pellets offer two different things to the composting process?
A: To answer your questions:
Deciduous trees harvest a lot of resources from these leaves before dropping them. Thus, the nitrogen content of autumn leaves is essentially zero. Fall leaves provide complex structural carbohydrates (you’d say fiber if this was a human diet). Cardboard and paper are examples of structural carbohydrates. And these carbs have the ability to cling to moisture and absorb the juicier parts of kitchen scraps.
Alfalfa is popular in animal feed (and in composting) because of the nitrogen it provides. Nitrogen is an essential component of protein. The animals that do the work in a compost heap are bacteria. Think of them as little water-filled balloons made of protein. The heat in an active compost heap is the result of the metabolism of all of these bacteria, collectively. A simple definition of metabolism might be if you eat you give off heat.
If there wasn’t enough nitrogen to support bacterial life, the fungi would do the job. They prefer drier conditions and have the ability to go beyond their core structures and collect scarce resources, like water and nitrogen. But they are much slower to work than bacteria.
I can assure you that you have a large supply of official red wigglers. Red wigglers are big enough to have a mouth, guts, etc. They eat and (frankly) poop. All organisms that eat with the mouth and have a gut digest food to extract the nutrients necessary for their vital functions. They extract energy by breaking carbon-carbon molecular bonds. What they do not need for their vital functions, they pass through in the form of excrement. As a result, all feces contain concentrated nutrients – which is why manure has been the traditionally popular source of fertilizer for agriculture.
Worms don’t do what alfalfa pellets do. Worms are nutrient concentrators; alfalfa pellets are a source of nitrogen. You can do one or both. I suspect that if you can afford to do both, you will have richer compost in less time.
– Linda Brewer, OSU Extension Floor Specialist
Q: What are the right resources for winterizing vegetable gardens? – Jackson County
A: Page 5 of this publication gives a good summary of the activities to do in the vegetable gardens in the fall.
In addition, this website from the University of Minnesota has some great ideas for fall vegetable garden activities.
If you want to grow vegetables in autumn and winter, this to guide is a great resource. – Danielle Knueppel, Assistant Professor of Practice, OSU Department of Horticulture
Q: Can I store my drained garden hoses on my covered porch or open-sided shed? I have a lot of it because of our sprinkler system. They take up too much space in our store / garage. – Douglas County
A: Storing pipes that have been drained on an open porch or shed at outside temperature is acceptable. They will not be damaged by frost. After draining, you can tie the ends to each other if you roll them up to make sure no bugs or dirt get into them. – Steve Renquist, OSU Extension horticulturalist