Pine needles are some of the toughest leaves out there, and they take a correspondingly long time to break down. They get there eventually, though, and depending on how you prepare and compost them; you might be able to speed up the process. The way you use the pine needles will also influence which method of composting is the right one.
Do Pine Needles Compost Well?
Pine needles, like other plant materials, make a great addition to your compost. They will be among the materials that take the longest to break down, but given enough time, they will completely decompose and integrate into your compost.
Are Pine Needles Acidic?
If you apply compost that still has large pieces of pine needles in it, those pieces may be lowering the pH level of your compost, making it more acidic. The more needles, the more chance they have of releasing enough of their tannic acid to affect the acidity of the compost. Always check the pH level before adding finished compost to your plants since different plants like different levels of acidity.
Regular compost, once it’s totally broken down, will be about neutral, near or around a pH of 7, or somewhere between 6 and 8. While it’s fresh and full of humic acids (which are released as material breaks down and which help materials decompose), it may be as low as 5. Pine needles, with an acidity of about 3.5, break down very slowly and may release tannic acids during that time.
Why Do Pine Needles Take So Long To Decompose?
Pine needles are evergreen leaves, and they have to be very tough and sturdy to survive both summer and winter. Their waxy coatings, high lignin content, and tannic acids result in a durable material that takes longer than average to break down. The waxy coating and lignin (a rigid, woody cellular compound) are difficult for bacteria and fungi to work through and break down. The low pH of the materials and tannic acids also can slow down the decomposers, which makes the composting process take even longer.
If you’re adding them to regular compost, the materials should be varied and diluted enough that the pine needles won’t affect the compost pH too much (you should check to be sure before using it, however). If it seems to be too acidic for your plants, you can allow it to decompose further until the pH level is at the level you need it to be.
This may take up to 4 months in hot compost or up to a year in a cold one (more on those later!) To speed up the breakdown process, the needles can be cut into smaller pieces using a garden shredder or your mower (with a mulching blade, preferably).
For ericaceous compost, the low pH level would be what you’re looking for. Acid-loving plants appreciate compost made heavily with plant materials on the acidic side. Similarly, pine needles can be used as mulch around acid-loving plants (including the pine trees they fell from).
What’s The Best Way To Compost Old Pine Needles?
Depending on how you want to ultimately use the compost, you have a few options on how to use your pine needles. The options to compost pine needles include:
- Hot compost
- Cold compost
Pine needles shouldn’t be used for vermiculture or worm composting. The tannins create a low pH environment that isn’t good for the worms, who don’t like such acidic conditions.
Hot composting is done in enclosed bins, tumblers, or on-ground heaps with a covering, like a tarp. The lids keep the heat and moisture in the compost, which creates a livable environment for the bacteria that break down the nitrogen-rich material.
The heat is given off by the bacteria, and the center of a hot compost pile can get up to 140 degrees Fahrenheit. The first few weeks of the composting process are heat-generating and dominated by bacteria that need to be aerated and given some water at least once a week. The latter few weeks of the composting process are dominated by fungus, which slowly breaks down the carbon-rich material.
Composting pine needles in hot compost can help speed up the time that the leaves need to be broken down. They can take between 2 to 4 months to break down in hot compost, and they’ll be among the last materials remaining to do so. If there’s a variety of materials in the compost, it shouldn’t affect the pH level too much. If you want to be sure the compost is closer to neutral, let the compost break down until the needles are gone completely. Remember, the smaller the pieces, the faster the decomposition.
A cold compost pile doesn’t heat up as much as a hot one does because it’s left out in the open air, which allows moisture and heat to be released. This keeps the bacterial population lower and the decomposition process slower. Pine needles can take up to a year to break down with this passive method, but it’s a useful option if you aren’t in a rush.
Your raked-up pine needles make a great mulch! A layer of pine needles allows airflow to the ground and protects the soil from wind erosion and compaction from watering and rain while keeping moisture in the topsoil. It also insulates against changes in temperature, making it an ideal winter groundcover for garden plants that like acidic soils. When you harvest your pine needles for mulch, make sure to sort out the rocks and twigs as best as you can to keep the mulch pure.
Can You Compost Pinecones?
While raking up your pine needles for compost, some pinecones might be found in the mix. You should remove pinecones from the lawn, so they don’t get chopped up when mowing (they aren’t easy on mower blades). The tough cones can be snapped in half or shredded in a garden shredder and thrown into your compost pile, treating the compost as you would with pine needles.
Wait a few months until they’re fully broken down if you want less acidic compost, or spread it sooner for an ericaceous compost that your acid-loving plants will love.