When it comes to coffee grounds in compost, how much is too much? Ask an expert

Gardening season is winding down, but you may still have some questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website, type it in and include the county where you live. Here are some questions asked by other gardeners. What’s yours?

Q (1 of 2): I was wondering if one could have too many coffee grounds in a compost pile?

I have a three-bin system and take in so many leaves from my neighbor’s yard each autumn (about 30 yard bags). This year, to help make sure I have a better balance, I’m getting a 5-gallon bucket of coffee grounds from a local coffee shop each week and am adding it to each bin on a rotating basis so that every third week each section will get the grounds in addition to my kitchen waste.

I was wondering if my overall compost pH will be relatively balanced if I’m mixing the grounds with this huge abundance of leaves or should I dial back on the grounds? – Multnomah County

A: Interestingly, when a compost pile is composed of primarily plant matter (leaves, food waste, coffee grounds), it begins at a low pH and rises to about neutral. Low pH because the decomposition of plant materials results in the release of organic acids – initially.

When a compost pile is composed primarily of animal carcasses, manures, blood meal, it begins at a high pH and falls to about neutral. High pH because readily released nitrogen may be in the form of ammonia – initially.

So the coffee idea is OK, but coffee is pretty low in nitrogen content, maybe 2-3% at best. In your situation, I’d consider going to the feed store and getting a 40-pound sack of alfalfa pellets. I’d sprinkle the pellets every 3-5 inches of depth in the pile of leaves. The breakdown of the alfalfa will contribute nitrogen and really get the bacteria in the piles working. Even better, if you could find a handful of red wiggler worms for each of the bins. One spring I found that I had 50 gallons of worm castings! – Linda Brewer, OSU Extension soil specialist

Q: (2 of 2) I don’t think I know what the range of nitrogen content is for leaves. Do you have that information readily available? 🙂

Also, my bins are full of worms, they are small and red, but I don’t know if they are the official red wrigglers. Do you think they are serving a similar service and could substitute for the alfalfa pellets? Or are the worms and pellets offering two different things to the compost process?

A: To answer your questions:

Deciduous trees harvest a lot of resources from those leaves before they drop them. So, the nitrogen content of autumn leaves is essentially zero. Autumn leaves provide complex structural carbohydrates (you’d say fiber if it was a human diet). Cardboard and paper are examples of structural carbohydrates. And those carbohydrates have the ability to hang on to moisture and absorb the juicier parts of kitchen scraps.

Alfalfa is valued in animal diets (and in composting) because of the nitrogen it provides. Nitrogen is an essential building block of proteins. The animals doing the work in a compost pile are bacteria – think of them as little water-filled balloons made of protein. The heat in an active compost pile is the result of the metabolism of all of these bacteria, collectively. A simple definition of metabolism could be if you eat you give off heat.

If there was not enough nitrogen to support bacterial life, the work would be done by fungi. They prefer dryer conditions, and have the ability to reach out beyond their central structures and collect scarce resources – like water and nitrogen. But they are far slower at the job than bacteria.

I can assure you that that you have a great supply of official red wigglers. Red wigglers are large enough to have mouths, guts, etc. They are eating and (frankly) pooping. All organisms that eat with a mouth and have a gut digest food to extract the nutrients necessary for their life functions. They extract energy by breaking carbon to carbon molecular bonds. What they don’t require for their life functions, they pass through as excreta. As a result, all fecal matter contains concentrated nutrients – which is why manures have been the traditional valued fertilizer source for agriculture.

Worms aren’t doing what the alfalfa pellets do. Worms are nutrient concentrators; alfalfa pellets are a source of nitrogen. You can do either or both. I suspect that if you can afford to do both, you will have a richer compost in a shorter period of time.

– Linda Brewer, OSU Extension soil specialist

Q: What are some good resources for preparing vegetable gardens for winter? – Jackson County

A: Page 5 of this publication gives a good summary of activities to do in vegetable gardens in the fall.

In addition, this website from the University of Minnesota gives some great ideas for fall vegetable garden activities.

If you’re interested in growing vegetables in the fall and winter, this guide is a great resource. – Danielle Knueppel, assistant professor of practice, OSU Department of Horticulture

Portland woman burglarized, flooded home of boyfriend’s ex, cops say

Drained garden hoses can be stored outdoors. Oregonian file photo.

Q: Is it OK to store my drained garden hoses on my covered porch or open-sided shed? I have many due to our watering system. They take up too much space in our shop/garage. – Douglas County

A: Storing hoses that have been drained on a porch or shed that is open to the outdoor temperature is fine. They will not be damaged by a freeze. After draining you can attach the ends to each other if you roll them up to make sure no insects or dirt get in them. – Steve Renquist, OSU Extension horticulturist