Pine needles in compost

Composting Pine Needles: How To Compost Pine Needles

Abundant and free in most parts of the country, pine needles are a great source of organic matter for the garden. Whether you use pine needles in compost or as a mulch around your plants, they provide essential nutrients and improve the soil’s ability to hold moisture. Once you know how to compost pine needles, you don’t have to worry about any adverse effects.

Are Pine Needles Bad for Compost?

Many people avoid using pine needles in compost because they think it will make the compost more acidic. Even though pine needles have a pH between 3.2 and 3.8 when they fall from the tree, they have a nearly neutral pH after composting. You can safely add pine needles to compost without fear that the finished product will harm your plants or acidify the soil. Working pine needles into the soil without composting them first may temporarily lower the pH.

Another reason why gardeners avoid pine needles in compost is that they break down very slowly. Pine needles have a waxy coating that makes it difficult for the bacteria and fungi to break it down. The low pH of pine needles inhibits the microorganisms in compost and slows down the process even more.

Using aged pine needles, or needles that served as mulch for a season, speeds up the process; and chopped pine needles compost faster than fresh ones. Make a mound of pine needles and run over them with a lawn mower several times to chop them. The smaller they are, the faster they will decompose.

Composting Pine Needles

One advantage to composting pine needles is that they don’t compact. This keeps the pile open so that air can flow through, and the result is a hotter compost pile that breaks down more quickly. The pine needles break down more slowly than other organic matter in a compost pile, even when the pile is hot, so limit them to 10 percent of the total volume of the pile.

A simple and natural way of composting pine needles is to simply leave them where they fall, allowing them to serve as a mulch for the pine tree. They eventually break down, providing the tree with rich, organic nutrients. As more needles fall, they keep the mulch looking fresh.

What is a leaf?

To a plant, leaves are food producing organs. Leaves “absorb” some of the energy in the sunlight that strikes their surfaces and also take in carbon dioxide from the surrounding air in order to run the metabolic process of photosynthesis. The green color of leaves, in fact, is caused by an abundance of the pigment “chlorophyl” which is the specific chemical agent that acts to capture the sunlight energy needed for photosynthesis. The products of photosynthesis are sugars and polysaccharides. An important “waste product” of photosynthesis is oxygen. To an animal, a leaf may be a food source or a place to live on or under (i.e. a “habitat”).

What kinds of leaves do we see on the trees found on the Nature Trail?

The leaves found on the trees of the Nature Trail are either broad and flat (like oak leaves) or needle-shaped (like red pine needles). Both kinds of leaves are photosynthetic organs and both kinds of leaves can serve as food or as habitat for a great variety of other organisms.

Why do tree leaves have different shapes?

The shape of a tree’s leaves are a response to the tree species’ long term ecological and evolutionary histories. An ecosystem’s limiting factors may also modify the finished form and shape of a tree’s leaves. Understanding of the “logic” behind the varied forms of leaves is facilitated by a firm grasp of the precise functions a leaf must accomplish.
1. A leaf must “capture” sunlight for photosynthesis (and as it does this it may also absorb a great deal of heat!)
2. A leaf must take in carbon dioxide from the surrounding air via pores (called “stomatae”). This carbon dioxide is also needed for photosynthesis. When these leaf stomatae are open to allow the uptake of carbon dioxide, water from inside the leaf is lost to the atmosphere.
The leaf, then, is affected by these balancing acts: enough sunlight and carbon dioxide to run photosynthesis, but not too much associated heat absorption or water loss.

How does this “balancing act” influence the ultimate expression of a leaf’s shape?

Leaves high in the tree canopy receive a great deal of sunlight. These leaves tend to be smaller in size (and, therefore, have reduced light absorptive surface area) and tend also to have complex edges and lobes (which enables them to disperse absorbed heat very rapidly). Leaves in the lower tree canopy are more shaded. These lower canopy leaves tend to be larger (more light absorptive surface area) and tend to have reduced expressions of lobes and edges. These trends may be observed in comparing the leaves of high canopy trees (like oaks) to the leaves of low canopy trees (like dogwoods), or they can also be observed in an individual tree that has leaves in both the upper and lower canopies (the white oak, for example). In the white oak the smaller upper canopy leaves are also noted to allow significant amounts of light to pass through the upper canopy in order to keep the lower leaves supplied with sufficient light to allow their continued photosynthesis.

Needle-shaped leaves have a very low light absorptive surface area. Each needle, then, is not able to capture very much sunlight energy for photosynthesis. Needles also have a very thick, outer cuticle coating and special “pit-like” stomatae designed to prevent excessive water loss. Trees with needle-shaped leaves are especially well suited to site’s that have drier soils and to climates in which the careful conservation of water is an important survival strategy. Needle-shaped leaves also differ from broad leaves (in our climate zone anyway) in that needles last for three or four years while broad leaves only “live” for a single growing season. These ‘evergreen” needled trees, then, have a great advantage over the “deciduous” broad leafed trees in that the metabolic cost of the leaf’s synthesis can be recovered via photosynthesis over several growing seasons. Also, the continuous presence of the needles means that whenever environmental conditions are sufficiently moderate (even in the middle of winter!) the needles can photosynthesize and thus gather energy for the tree! A study in Germany compared energy production in beech trees (which have broad, flat leaves) and Norway spruce trees (which have needles). It was found that the beech trees photosynthesize for 176 days in a year while the Norway spruce photosynthesize 260 days in a year! The bottom energy line was that with this increased time base for photosynthesis, the smaller leafed surface area of the Norway spruce was actually 58% more productive than the beech!

Are the arrangements of leaves on a tree always the same?

There are two basic arrangement patterns of leaves on a tree: “mono-layer” and “multi-layer”. In a mono-layer arrangement the leaves are arrayed so that no leaf is above and, therefore, shading any other leaves of the tree. This is the leaf pattern seen in the shade dwelling under story trees like the dogwood. In a multi-layer arrangement there are leaves above and below other leaves on the tree. This is the pattern seen in trees which extend u into the upper stories of a forest canopy. The light-rich upper leaves (as previously mentioned) tend to be smaller and more lobed than the lower. This leaf shape facilitates heat loss and prevents extreme self-shading.

Using Pine Needles in Your Garden

Article: Using Pine Needles and Leaves in Your Garden

December 15, 2009

Every year in autumn, trees shower gardeners with an abundance of falling leaves and pine needles. To not take advantage of them in our gardens is to waste some valuable (and free) renewable resources. Here are some tips on how to use pine needles and leaves in your garden.

Leaves, Pine Needles, and pH

Changing the pH level of the soil can inhibit a plant’s ability to absorb some nutrients, but tests have shown that leaves and pine needles can only create a very small change in the soil’s pH when used as mulch or for winter protection. Whether or not these small changes will affect your plants depends a lot on your local climate conditions (how fast the leaves and pine needles decompose) and the pH of your existing soil.


If you use nothing but large amounts of leaves and pine needles over a period of several years, adding lime every few years will help counteract any acid buildup. Always let a soil test be your guide to making any adjustments. Fully composted leaves and pine needles are considered neutral and will not add to the acidity of your soil.

Using Pine Needles

As a mulch. Because of their shape and rigidity, pine needles naturally lock together, which allows air and water to circulate while preventing the needles from packing down and forming a dense mat. This means your plants are far less likely to experience the rot and oxygen deprivation that sometimes occurs under thick layers of bark or leaves. The shape and rigidity of the needles also helps the mulch stay put during high winds and steady rains. Pine mulch can be used around vegetables and perennials of all kinds including roses and raspberries.


As winter protection. Add 3 to 5 inches of pine needle mulch to your garden beds in the fall. This will provide protection against sudden and extreme dips in temperature and allow plant roots to remain active until the ground freezes.

As a slug barrier. Create a ring of pine needles around the base of your hostas to help prevent slug damage. Pests like slugs and snails are known to avoid crawling over prickly objects that could injure or irritate their soft bodies.

As a walking path. Use pine needles to create walking paths between the rows in your vegetable garden. After you walk them a few times the needles pack down nicely. Not only do pine needles make an attractive path, but it will also help to keep the weeds from growing in-between your rows.

Using Leaves

On your lawn. Run a mulching mower over them and let the leaves fall where they may. By chopping them up you’ll be adding a thin layer of organic nutrients to your lawn, and you’ll also save yourself some raking. If you don’t have a mulching mower, simply raise the front wheels of your lawnmower by a notch or two and take several slow passes back and forth across your lawn. You can also put them in a tall plastic pail or garbage can and chop them up with your weed whacker.


To make leaf mold. Leaf mold is sometimes called garden gold and making it is simple. Collect leaves and drop them into a holding cage made from poultry wire wrapped around stakes pounded into the ground. If the leaves are dry when you collect them, wet them down with a hose. Now leave them there to decay. Next fall you can use your one-year-old leaf mold as a mulch, or allow it to decay for another year and use it to condition your soil.

As winter protection. Newly fallen leaves can be used as winter protection around plants, but need to be removed in spring to avoid smothering plants. Shredded leaves will decompose faster, but may also still need to be raked out in the spring. To prevent leaves from blowing away, cover them with pine branches.

“We want to demonstrate that they’re a great source of carbon and a good amendment to make your garden grow better,” he said. “We want to document that it actually happens.”

McConnell said the results of his study could have application for forestry and agriculture. It’s a way to use pine needles, he said. A farmer in the Columbia Basin uses three truckloads of pine needles for his irrigation circle, McConnell said.

“If you add organic matter to soil. You increase the moisture-holding capacity and the ability to buffer against climate change,” he said. “There’s applications out there, we just need to figure out how to do it.”

McConnell uses different materials: 110 pounds of Ponderosa pine needles, 23 pounds of dry leaves, 67 pounds of grass and 110 pounds of coffee grounds. Colleagues, local lawn care services and coffee shops provided the materials.

In some cases, the pine needles were shredded and left lying in a yard for a year. Some pine needles are freshly collected and intact. McConnell will compare composting rates depending on treatment, monitoring temperature.

WSU Extension volunteer and master composter Ryan Herring expects the project to demonstrate pine needles increase fungal activity.

Herring said the project shows how much organic matter trees can produce, and the protection they offer against erosion. Farmers on the Palouse may wish to start planting more trees, as using their byproduct in the soil would have a huge benefit, he said.

“An acre of trees versus an acre of grass, you’re going to get a lot more carbon and organic matter from the tree,” Herring said. Over time, trees will output more than the grass, he said.

Ponderosa pine needles are acidic, another reason gardeners don’t usually use them, but McConnell said composting neutralizes them so that they don’t acidify the soil. He will closely monitor soil pH.

The current project will last 90 days. McConnell uses funds he has access to for the project, but is interested in finding sponsors.

There are a lot of mismatches when it comes to composting, he said. Both brown and green materials are necessary, which requires timing.

“Composting is kind of an art and a science,” he said.

Do pine trees and pine needles make soil more acidic?

A very common gardening myth is that pine trees and the needles they drop acidify the soil. While it’s true that the soil near pines is often quite acidic, the soil pH was not determined by the tree. Eastern white pine (Pinus strobus) is one of the dominant forest tree species in much of New Hampshire, and it grows best in places with acidic, well-drained soil. Pines grow where they do because the soil and climate are suitable, and they are not creating acid conditions themselves. When nothing grows beneath a white pine tree, it is probably because the tree has numerous shallow roots and is casting too much shade.

Benefits of Using Pine Needles As Mulch

Pine needles themselves are acidic but do not have the capacity to appreciably lower the soil pH. To do that, it is necessary to incorporate a soil acidifier such as sulfur or aluminum sulfate. If you are unsure of the pH in your garden, you should have the soil tested. As pine needles break down and are incorporated into the soil, decomposing organisms gradually neutralize them. Thus, there is no harm in using pine needles to mulch shrub borders, flower beds and vegetable gardens. Even a 2 to 3 inch layer of pine mulch will not change the soil pH enough to measure.

There is a long list of benefits to using pine needle mulch, including that it is free and often readily available. Pine needles provide all the advantages of any other mulching material, including conserving soil moisture, suppressing weeds, adding soil nutrients, moderating soil temperature and keeping plants and fruit clean during heavy rains. Additionally, pine needles have a tendency to stay loose and light, not forming an impenetrable crust like wood mulch. They are quite stable and do not tend to wash out of beds during heavy rains. In spots where it is difficult to keep mulch in place on a slope, pine needles may be the answer. Finally, pine needles are longer lasting than other types of organic mulch, and their fine texture is quite attractive against most permanent plantings.

If you have a pine tree in your yard, start taking advantage of fallen needles. They are a free mulch and will benefit your garden.

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Pine Needle Acidity: Myth or reality?

he most convincing fact for me is right there in that bed of salvia (photo below). When I inherited the bed over 20 years ago, the soil in it tested at a pH of 7.0. This is the ideal soil pH, because so many plants do well at this level, which is neither acid nor alkaline. The exceptions are acid-loving plants such as azaleas, camellias, and blueberries and alkaline-loving plants such as cosmos, daylily, and foxglove (see also table at right below). I’ve mulched the bed with pine straw for every one of those 20 years. Today, especially for this article, I measured the pH again. The meter registered at 7.0, exactly where it was when I started the bed so many years ago.

The salvia bed in question

Here are some other facts to consider:

  • Pine straw in itself is slightly acidic at 6.0 – 6.5.
  • Normal rain water tests at 5.6.
  • So why hasn’t the soil at a pH of 7.0 in the salvia bed become more acid?
  • Soil is not a static medium. Its components react with one another. In the case of rain water and pine straw, those interactions have a neutralizing effect on their initial acidity.
  • Research by others, more carefully and scientifically done than my experiment with the salvia bed, shows both small increases and small decreases in soil pH from using various mulches such as oak leaves, pine straw, and shredded cedar. However, the changes were so minuscule that they were totally insignificant, and there was no negative impact on plant health.

nother issue sometimes raised in the pine-straw-as-mulch debate is that of terpenes in the needles. Terpenes are chemical molecules said to retard germination and new growth. Since I don’t mulch seed beds and use pine straw only in established beds, retardation of germination is a good thing. It helps to keep weed seeds from germinating.

The terpene effect turns out to be short-lived. Terpenes dissolve readily in water and dissipate into the air, leaving behind only trace amounts that may discourage germination but certainly don’t harm established plants. By the time pine needles are brown and dry, most of the terpenes have evaporated. Once that wonderful pine fragrance has gone out of the needles, so have the terpenes, the source of that fragrance.

So why is pine straw a good mulch? Let me count the ways:

1. It lasts a long time. Pine straw doesn’t float and wash away. It breaks down more slowly, so it doesn’t need to be reapplied as often as other mulches.
2. It’s lightweight, lighter per cubic foot than most other mulches. The bales are easy to carry and offer more coverage for the equivalent weight of other mulches.
3. It’s sustainable. No trees are harvested to produce it.
4. It promotes soil health. The soil breathes better, doesn’t compact, and allows for better water infiltration with pine straw than with other mulches.
5. It promotes plant health. Its decomposition adds organic material and nutrients to be taken up by plants.
6. Its uniform color and fine texture is visually appealing.
7. It doesn’t attract termites.
8. It’s easy to apply.
Find these tips and more info here

Note how the pine straw helps to unify the
various elements in this garden bed.

For me personally there is a no. 9 reason or perhaps I should make it the number one reason I use pine straw. It’s free! I’m fortunate to have free access to a nearby source. If you’d like to try pine straw, but don’t have any pine trees on your property, scout around to see who does. If you don’t mind being a bit forward, ask the owner/owners if they use their pine straw. If not, or if they have a surplus, ask if you may stop by to collect some.

ther sources for pine straw include your local nursery or garden center. Pine straw is generally sold in bales. The needles in the bales are compacted. When you untie a bale, you’ll be amazed at how much the needles expand and how much coverage a single bale will provide. Failing local sources, you can also find pine straw online. Here are a few sources: By the box, By the bale, By the bale.

Pine straw bale. Bales come in different sizes and

nd the larger question: Why mulch at all?
At this time of year (fall) my number one reason to mulch is the prevention of alternate freezing and thawing of the soil between now and spring. This process can lift plant roots right out of the soil and is called “heaving.” Our strawberry bed, in particular, is subject to heaving, so we make sure to cover it with at least three inches of pine straw every fall.

Other reasons to mulch:

  • It helps prevent loss of topsoil from wind and water erosion.
  • It reduces water usage by maintaining soil moisture.
  • It reduces rainwater runoff.
  • It reduces soil compaction.
  • It improves soil tilth.
  • It makes the landscape more attractive.
  • It reduces weed growth.
  • It insulates soil to keep plants cooler in summer and warmer in winter.
  • It improves soil fertility.

DG Photo Credits:
Eastern White Pine by catcollins
Loblolly Pine by trois

*See recent article by DG writer, Sharon Brown

Pine needles make a great mulch, but do they make soil acidic, or is this a gardening myth? Patrick Dolan and I share our thoughts on the topic.

Question 1: I’ve always heard that I could use a pine needle mulch to acidify the soil for blueberries and other acid loving plants, but a viewer recently sent me a link to research from xyz that indicates pine needles do not significantly increase soil acidity. What are your thoughts?

Response 1: Although it is thought to be a common conception that pine needles acidify soil it is in fact likely not the case. Even universities such as Cornell make reference to pine needles acidifying soils when used as a mulch. Pine needles are typically acidic in nature. During the very slow decomposition process pine needles lower from a pH of around 3.5 to nearly neutral 7.0. The mulch itself may be acidic however with minimal transfer to the surrounding soils. Generally soils have a neutral pH of 7.0 and are able through their own chemical to buffer any pH transfer from the needles. I have attached an information sheet from Washington State University as a reference.

Question 2: But if pine needles don’t make the soil more acid, why are the soils in pine forests often more acidic?

Response 2: Typically soils in pine forests are slightly acidic due to a number of features. The Boreal Forest spans Northern Latitudes from Canada, Russia United States and the Scandinavian Countries. A major feature in the Boreal forest of Canada is the presence of bogs and fens covered in a dense canopy of pine trees.

Soils in the boreal forest decompose slowly due to the low temperatures and limited microorganism activity. The dense canopy and annual precipitation rates result in low water evaporation is limited. This soil is often left water logged allowing limited nutrient cycling compared to southern forest types.

The longer the water is in contact with the mineral base the easier it is for elements to leach into solution and move into different layers of the soil. Elements like iron and aluminum leach from the A horizon (the top) to the B horizon (below A) followed by clay. That leaves the A horizon with a sandy neutral mineral content. Once this migration happens the elements and cations that buffer the addition of acidic material move lower allowing for the acidification of the A horizon.

The low decomposition rate, influence of the water regime and the aerobic situation, tannins and other acids materials decrease the pH of the boreal forest soil

Question 3: You said that the pine needle mulch is acidic and does not transfer. If I mix it into the soil would that lower the pH?

Response 3: unfortunately no. Pine needles decompose very slowly and even in situ will not transfer acidity to the soil.

Question 4: What can I do to lower the pH of the soil.

Response 4: I am glad you asked. There is a number of ways you can lower the pH of your soil.
Peat is a great way to lower the pH. If you grow in a peat mix of use peat to top dress the soil it will help lower it.
The second and the most effective is sulfur amendments. Elemental sulfur does require time to be converted to sulfuric acid with the help of the soils microbes.

The third and final method I use is cold black coffee. Cold coffee has a pH of around 5 and acts as a weak organic fertilizer. Much like an extraction compost tea the organic material that makes coffee so fantastic are also available to both the plant and the resident microorganisms. Just as an aside although used coffee grounds do not have the acidity that the coffee does they do add some fantastic N P K and can typically be picked up for free at local coffee shops.

There are other organic ways to lower the pH. From the most acidic to the least Lemon, vinegar, orange juice, tomato juice, black coffee. I do recommend if you are going to use anything else do the research and test out your application methods on some soil before applying it to your garden.
It is important to note it is recommended to avoid trying to drop the pH of your soil more then one point per year. If your soils are alkaline or have a lot of clay in them the pH will recover over time as the basic elements interact with the acidic ones to neutralize each other.

Please see the links to sources on this topic below:

Links provided by MrChipGardener:

Forest Industry Council –….

Washington State University –…

Colorado State University Extension…

“Decoding Gardening Advice”, p. 49…

Wood Chip Mulch: Landscape Boon or Bane?

Acid Rain Effects – Soils…

Pine needles make good mulch so much so that a new product called pine straw mulch has emerged as a good mulch for areas exposed to heavy rain. It’s inexpensive, lightweight, and instead of washing away as other mulches do, it knits together to form a protective mat. Among the many types of mulch, pine needles are an excellent choice for the home garden.

Pine Needles Make Good Mulch for Gardens

Pine needles make good mulch for gardens and landscapes.

Reasons to Use Pine Needle Mulch

There are many reasons to use pine straw or pine needle mulch. These include:

  • Water conservation: Pine needles form a thick, protective mat during heavy rains. This allows moisture to penetrate the pine needles but prevents erosion, trapping water where it’s needed near surface roots. They also reduce rainwater runoff and make an excellent mulch for hillsides.
  • Weed prevention: Like most mulches, a thick layer of pine needles suppresses weeds. Many weed seeds need light to germinate. Mulch prevents such seeds from sprouting. It also prevents wind borne seeds from sprouting because it forms a barrier between soil and seed.
  • Improves the soil: Pine needles decompose and add organic material to the soil. They also aerate the soil and improve drainage as they decompose. Pine straw mulch may also help regulate the soil temperature. Just keeping the soil a few degrees above freezing for a few days longer in the fall can actually extend the growing season. And unlike bark mulches, it does not add excessive minerals to the soil. Some hardwood mulches can add too much calcium and other minerals to the soil.
  • Ecologically sound: Pine trees shed their needles annually, forming a thick carpet on forest floors. To harvest and create pine straw mulch, the needles are simply raked or scooped up, processed, bagged and sold. Trees do not need to be cut down or put through a chipper as is done to make hardwood mulch, pine bark nuggets or other wood chips. Trees can continue to grow for many years to come. The trees may eventually be harvested, but foresters get more years of growth from them. Pine mulch also beats down slower than other mulches, so your investment lasts longer than typical hardwood or bark mulches.

Buying Pine Bark Mulch

Now that you know the answer to the question, “Do pine needles make good mulch,” you may be curious about how to purchase or use it. If you’re fortunate enough to live near a large pine tree, you can scoop up some of the needles to use as mulch. It’s much easier to purchase bags of pine straw mulch at the garden center. You can purchase pine bark mulch at home and garden centers nationwide, large retailers and nursery and garden centers. It’s very lightweight too, so as an added plus you might not need help carrying bags out to your car!

How To Use

Spread pine bark mulch as you would any mulch, around shrubs, trees and plants in the garden. It may be purchased in bales or bags. To calculate how much to buy, consider that you will need approximately half a pound of pine straw or pine needle mulch for every square foot of garden space. Spread it in a layer about two inches deep. It settles and compacts over time.

For more information about pine mulch, please see:

  • Texas A & M University’s Cooperative Extension pamphlet, which is free for you to download.
  • Pine Straw Info, everything you need to know about pine straw on one website.

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