Do Pine Needles Make Good Mulch?

Adding a layer of mulch to your garden not only helps beautify the space but also benefits the plants and surrounding environment. But with so many different types available, which material should you choose?

If you live in an area with lots of pine trees, the needles are a readily available and affordable resource. Pine needles, also known as pine straw, cover the ground as well as wood chips, straw, and other common types of mulch.

I’ll explain the benefits and drawbacks so you can make the decision for yourself. Plus, I’ll clear up a few common misconceptions surrounding using pine straw as mulch.

The Long Answer

Pine needles make great mulch in most gardens. However, before you decide to use them, consider the following factors.

The Benefits

The needles from pine trees provide many of the same benefits as other types of mulch, plus a few unique advantages, depending on where you live.

Since they are organic material, they break down and enrich the soil. They’re a great option if you want to avoid the waste and energy use associated with plastic mulches and landscape fabric.

Another benefit is their light and fluffy texture. Since the needles don’t compact as much as materials like leaves and wood chips, they are less likely to form a dense mat. Therefore, water and air continue to flow in and out of the soil, limiting anaerobic conditions and flooding. Plus, their light weight means they’re easy to spread!

Pine straw is also an inexpensive material, especially if you live in an area with many pine trees. Since the needles are rather light, you can rake, bag, and transport them to the area you’d like to mulch. And if you don’t want to collect your own needles, you can purchase bales of pine straw at home improvement stores and garden centers.

A final benefit of pine straw is its durability! Even with adequate moisture and warm temperatures, a few inches on a garden bed will take one to two years to break down. Therefore, you only have to apply pine straw once each year. Since the long life is due to the waxy coating on the outside of the needles, forego shredding needles.

The Drawbacks

While pine straw is easy to find in areas with many pine trees, it’s difficult to acquire in areas filled with deciduous trees or barren landscapes. If you live in a place with lots of maples, oaks, or other deciduous trees, consider mulching with leaves instead.

Depending on who you ask, the natural reddish-brown color is another potential drawback. While I find this terra cotta color delightful, it may not fit what every gardener is looking for.

Impact on Soil pH

If you hang around gardening circles long enough, you’ll hear some people mention that pine needles decrease soil pH. In other words, they make the soil more acidic. But is this claim true?

There’s no denying that these needles have an acidic pH. Their pH falls between 3.2 and 3.8, while a neutral pH is 7.0. However, adding them to the top of the soil doesn’t necessarily raise the pH.

When you watch them break down on top of the soil or in a compost pile, it’s easy to think this pH process magically occurs. But a collection of invisible microbes are the powerhouses running the show. These bacteria and fungi work to break down large particles and neutralize acidic and basic substances. That means that once composted, they have a close to neutral pH.

Looking for proof to back this up? Then, look at a study conducted by folks at Washington State University Extension. These experts sought to examine the use of ponderosa needles as a carbon source in compost making and address citizens’ concerns with the needles’ waxy cuticles and low pH.

The experimenters mixed each type of pine needle with coffee grounds, grass clippings, and dried hardwood leaves, then placed each mixture in GeoBins designed for home composting. They completed four replicates for each group.

Within three months, all of the GeoBins contained compost that was ready to use in the garden. Not only did the materials break down, but the pH of each compost was at or near neutral. That means you can compost them without worrying they will create acidic compost. Similarly, you can rest assured that using them won’t drastically lower the soil pH.

You may still be wondering why the soil pH below pine trees is acidic. While it’s easy to assume pine needles lower the soil pH, remember pine trees can only grow in acidic soil. Therefore, they only appear where the soil was acidic before their arrival.

Considering Type

While all types are similar in composition, each pine species produces unique needles. Some pines, like the eastern white pine, red pine, and ponderosa pine, have needles that are multiple inches long, while trees like the Jack pine and shortleaf pine sport shorter needles. All types have a similar texture, but larger needles are a little bit easier to collect.

You don’t need to cut down branches to obtain the needles. While all pine trees are coniferous, they slowly shed their needles as they grow. These fallen needles collect on the ground, where you can easily rake them into piles and then transport them to your desired location.

How to Apply

First, determine how much you’ll need. Measure the length and width of your garden (or whatever area you want to cover), then multiply the two numbers together to determine the area. Each bale of pine straw will cover about 40 square feet if you apply it at a rate of two to three inches. So, if your garden is 20 feet by 6 feet or 120 square feet, you’ll need three bales of pine straw.

Once you have your straw on hand, it’s time to spread it. While you can apply it any time of the year, spring is an ideal time since it allows you to smoother weed seeds that have yet to emerge. Plus, by covering the ground while plants are still small, you’ll avoid water splashing up from the soil surface and, therefore, limit the spread of disease.

You can apply mulch either before or after you plant annuals in the spring. Spreading it before planting limits the need for precision. However, you’ll need to push back the mulch from areas where you’d like to plant. If you choose to mulch after you plant, make sure to leave small plants uncovered.

No matter which option you choose, aim for a depth of two to three inches. This prevents weeds, conserves moisture, and stabilizes temperature without using excess material. I find the best way to spread pine straw is to shake it over the soil with my hands. However, you can also apply it with a hay fork.

As long as you apply the proper amount of material, you only need to reapply pine straw once a year. If you see a few bare spots in between major mulching events, just sprinkle some more to cover the soil.