Outdoor gardening with JoAnne Skelly: Composting pine needles
Submitted by Jeff Munson on Sun, 11/29/2020 - 3:19pm
On our walk today I was commenting to my husband “I can’t believe two pine trees could lose that many needles!” This was after I spent a number of hours raking the needles up from the driveway. My next question was “Can I compost pine needles?”
I have tested the soil on our property and found it to be alkaline, with a 7.8 pH. Some people think that pine needles make a soil pH so acid that plants will be damaged. Actually, according to Oregon State University Extension Service horticulturist Amy Jo Detweiler, that is a myth. While the pH of pine needles is 3.2 to 3.8 (neutral is 7.0) when they fall from the tree, if they are incorporated into the soil immediately, there might be a slight drop in soil pH, but it won’t damage plants. Needles in the soil or left on the ground are decomposed by microorganisms that neutralize their low pH.
Dr. Detweiler says “You can also add them to a compost pile; they will slowly break down over time. If you run them through a shredder, they will break down faster. A general rule of thumb is not to add more than 10 percent of pine needles to your compost pile.” It is possible to use pine needles for a couple of years as a mulch on the soil surface and then compost them too. This helps break down the waxy coating that otherwise slows decomposition.
If you have an active, healthy compost pile, just add pine needles to it and follow your normal mixing or layering techniques. Aged pine needles decompose more quickly than fresh. You can run a mower over fresh needles to facilitate breakdown if you want to add them to a compost pile without seasoning them.
You still have to follow the guidelines to keep the pile decomposing such as adding green nitrogen-rich material, some brown carbon-rich material, water, heat and air plus turning the pile periodically. Stick to the 10 percent limit Dr. Detweiler suggests and your composted needles and other materials will break down into nutrients available for plants to use next spring. Keep the center of the compost pile warm through winter by covering it with layers of leaves, straw, or newspapers and finally a tarp.
I wish everyone a happy, peaceful, and hopefully healthy Thanksgiving and holiday season. I am taking a break from writing articles this winter and plan to have my next article out the week of January 4, 2021.
— JoAnne Skelly is an Associate Professor & Extension Educator Emerita at the University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.
