Mulching with coffee grounds

I’m looking for a good free mulch to build my soil over winter. I have access to large quantities of spent coffee grounds (both my daughters work at Dunkin!) and sawdust from untreated wood. Also some leaves. I’m thinking of mixing them as mulch. However, last year i mulched a small area with shredded leaves and coffee grounds and nothing grew well there this summer. The top layer did not decompose by spring, although the layer underneath looked great and was full of worms. I have read a few different things about coffee grounds, so I’m wondering if they might have caused the problem. Does anybody have any experience with this?

Welcome to the forum!

What kind of sawdust did you use, maybe pine?  Pine might not be good for growing things.

Coffee grounds are acidic so using them as mulch might depend on what kind of soil you have.

I save all my coffee grounds to add to my soil as an amendment.

One year the weather was not good so I just dumped all the coffee grounds on top of some grass I wanted to kill.  That worked though I am not sure if it was the acid or the thickness of the coffee grounds.

You might find this of interest:

Bryant said, "Here are some useful characteristics of used coffee grounds. They are:

•High in nitrogen (a very valuable nutrient for plants). Grounds have a C/N (carbon:nitrogen) ratio of 20/1.
•Almost neutral (although coffee is highly acidic, the pH level of the grounds are diminished significantly when brewed)
•Digestible by worms
•Good for improving soil tilth (structure)
•A natural pesticide (great for repelling slugs, flies, and other critters!)
•An agent for bacterial control. The natural mold and fungus on coffee can suppress pathogenic fungi, including fusarium, pythium, and sclerotinia species.
•Weed killers

https://permies.com/t/45126/Coffee-Grounds

Hi Salwa,
Welcome to Permies. You are definitely on the right track to build up the soil.

I agree with Anne that the coffee grounds are a good soil amendment. I would use smaller amounts, as too much too fast, can cause problems.

Sawdust is similar, in that too much too fast can be a problem. Because the pieces are so small, it can crust over and cause problems. But small amounts that are allowed to break down should be fine.

In a perfect world, I like those woodchips from the arborists because it comes in different sizes, and does not pack down as much while it decomposes.

I have used them as mulch in the past with mixed results. Legumes are suppressed by coffee grounds and other high Nitrogen mulch, so that is a downside. It also releases N quickly, so it causing a flush of succulent cold vulnerable growth is not what I want around my perennials I would like to go dormant soon. I will use the hundreds of pounds I have collected in my next johnson-su compost pile, along with weeds, woodchips and leaves. This
mix seems to make great compost/wormcastings in about a year with no turning.

Thank you for all your suggestions. My sawdust is really more like fine chips, a mixture of woods- I’m not sure what but I’m pretty certain it doesn’t contain a lot of pine. I get it from a guy who chops logs for firewood. I didn’t use it last winter, I just used chopped leaves, but I have used it quite a lot this last summer and it seemed not to be a problem.
I guess I’ll just use a thin layer of my sawdust and coffee mix and try to add other stuff - I just have a shortage of compost and don’t want to have to spend a lot of money buying it! (And my supplies of coffee grounds and sawdust are pretty much unlimited!)

I've used coffee grounds a lot and noticed that if you put a layer on top of the soil it can become a relatively impermeable layer on top of the soil for quite a long time. I've just started mixing it in a little more, or adding less initially so that the layer doesn't form. I use it on my soil that has pine/spruce logs with chips and it does very well as long as it's mixed in. My citrus trees and blueberries love it. So it's probably not a great top mulch but more of a soil amendment.