Pine trees are evergreen conifers that add majesty and beauty to the landscape. They are also an abundant source of organic material since they shed their needle-like leaves year-round, unlike deciduous trees, which lose their leaves only in the fall or early winter.
Even though pine trees are a never-ending source of carbon material, some gardeners are reluctant to add them to the compost pile because they are concerned the needles will make the compost acidic (lower the soil pH and, by implication, make any soil the compost is added to acidic as well. But is this fact or fiction?
Do Pine Needles Make Compost Acidic?
Soil pH is an important factor in growing a healthy garden. While some plants thrive in a more acidic environment, most vegetable plants prefer a soil pH of 6.0 and 7.5. (You can learn more about the importance of soil pH and the preferred range for numerous vegetable plants in this helpful article.)
While it is true that fresh, green pine needles, also known as pine straw, have an acidic pH that measures between 3.2 and 3.8, they actually lose acidity as they decompose. After a period of only three to four weeks, they will have a pH that is almost neutral. Thus, contrary to popular myth, you can safely add pine needles to the compost bin without being concerned about increasing the pile’s acidity.
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How to Compost Pine Needles
Pine needles take longer to decompose than deciduous tree leaves because they are coated with a natural resin that protects them during the cold winter months. The waxy coating makes it difficult for microbes to break down the organic matter. As a result, they decompose slowly and, when added to the compost pile, can cause it to slow down.
If you have an abundance of pine needles, but do not want to slow the compost pile down, you create a separate pile of the slender needles and allow it to age over time. As it breaks down, you can then add the material to your main compost pile.
A faster option is to rake the needles into a pile and run a lawn mower over them. The smaller pieces will then decompose faster. Alternatively, you can run them through a shredder to achieve the same outcome. What’s more, you can do a combination of both methods: allow them to age for a season or two and then shred them before adding them to the pile.
Regardless of the method you choose, it is important to limit the amount of pine needles you add to no more than ten percent of the total volume of the pile since it is best to use a broad mixture of compost ingredients.
Benefits to Using Pine Needles in the Garden
In addition to being a good source of organic carbon (brown) material, there are other benefits to working with pine needles. The first is aeration. Unlike the leaves of deciduous trees, the shape of the needle-like leaves helps them resist compaction. This creates pockets of air, which, in turn, allows the pile to heat up faster. (You can check the temperature of your compost with this compost thermometer.)
Another benefit to having access to pine straw is that it can be used as an inexpensive organic mulch that helps the soil retain moisture while suppressing weeds at the same time. As the layers of mulch break down, you can add them to the compost pile.
It is important to note that if you incorporate pine needles into the soil, as opposed to simply laying them on top of the soil, it will increase the soil’s acidity (lower the soil’s pH). However, the change will be very slight and only temporary.
Some may still question why plants do not grow very well at the base of pine trees if the soil does not remain acidic. The answer is because pine trees have shallow roots, and plants placed under the trees must compete for nutrients. Often the plants lose out to the larger and more numerous tree roots. What’s more, pine trees create shade that many plants are not able to grow in.
So, can you safely add pine needles to the compost pile? Absolutely! Start taking advantage of this natural resource today!
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