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Gardening lore saying that pine needles are bad for compost and the garden has been around a long time. But this doesn’t make it true. In fact, I wasn’t even aware of the concerns most people have with composting them when I started adding them to my pile. In my regular method of action, I went ahead and piled in a bunch of raked-up pine needles and then decided I better do some research and find out if I had ruined everything. As it turns out, I hadn’t!
Both pine needles and pine cones can be composted but take a long time to break down. The idea that they are acidic and lower the pH of your soils has been tested and disproved in controlled conditions. Moreover, they are considered a good carbon source (“brown”) composting ingredient.
Although It is true that pine needles and pine cones can take a long time to break-down completely in a compost pile, there are ways around this problem. For example, using a hot composting method or chopping up the pine needles will considerable speed up the process.
Here is the full version of what I’ve learned on the topic in the past weeks on how to compost pine needles and pine cones, along with ideas on other ways to use this type of organic matter in the garden.
How to Compost Pine Needles
Just like composting anything else, successfully composting pine needles starts with making a compost pile with the right ingredients:
• A heap, bin, or tumbler of the correct size for the volume of organic matter,
• Sufficient amounts of water and aeration,
• Approximately 2 parts ‘green’ to 1 part ‘brown’ organic matter.
When you compost dry pine needles or pine cones, consider them part of the ‘brown’ or carbon part of the ingredients when you start. If you are composting green pine needles fresh off the tree, count them as part of the pile’s ‘green’ or nitrogen content. Limit both fresh and dry pine needles to about 10 percent or less of the pile.
A rule-of-thumb for testing water content in a compost pile is to squeeze a handful and see if you can get a drop of water out of it. If so, your moisture content is about right. The microorganisms needed for composting pine needles, pine cones, and everything else requires about 50 percent water by weight in the mix, and this test helps you get that result.
If you are composting pine needles in a pile or outdoor bin, a minimum size of approximately three cubic feet is required to get the compost pile to heat up.
Another way to use pine needles in a compost pile is to put a thick layer of them at the bottom of the pile when you start building it. The pine needles then help to get air into the pile. Avoid mixing the layer of pine needles in to the rest of the compost when you turn the pile.
A few visible remnants of pine needles in finished compost is not a problem in most cases. Incompletely broken down pieces continue to decompose in the soil, adding nutrients and organic matter as they rot.
If you make compost with pine needles and don’t like the undecomposed pine needles in the finished compost, you can sift out any pieces too big for your liking and toss them back in the pile for another round.
Fast Methods for Decomposing Pine Needles
Pine needles and pine cones have a waxy outer coating and a low pH, making them naturally resistant to the microorganisms needed for decomposing. You can speed up the process in several ways.
Pre-digest pine needles for faster composting
One way to speed up the composting of pine needles is to let them rot in a separate pile for a couple of seasons before adding them to the regular compost pile. Just rake them into a pile by themselves, and let them sit.
The sun, rain, and passing of time will break-down the waxy coating and raise the pH level. Then, when you add them to the composting process, they will decompose faster.
Using ‘hot’ manure to compost pine needles
Another way to speed up composting pine needles is to mix them with ‘hot’ manure. When it comes to animal manure, ‘hot’ means the organic matter contains a lot of nitrogen. Fresh manure is highest in nitrogen.
Manures with the highest nitrogen include:
However, do not add any of these fresh manures directly to garden soil, or you can do real damage to your garden. Instead, mix hot manure with pine needles and other carbon sources, such as straw, and turn everything into compost first.
Whenever you compost pine needles, use only about 10 percent pine needles in the total volume of ‘green’ and ‘brown’ matter for best results.
Shredding pine needles before composting
You can also speed up the composting of pine needles by chopping them up before you compost them. For example,
• Run pine needles through a shredder.
• Pile them up and run over them with a lawn tractor.
• Use a power lawnmower to break them up.
The more surface area the pine needles have, the faster they decompose when you add them to a composting system.
Cold Composting Pine Needles
If you don’t have access to fresh, high-nitrogen manure or don’t want to deal with the mess and odor of hot compost, you can also successfully compost pine needles in a cold compost pile. However, be prepared to wait a long time for them to break down completely.
Add small amounts (10 percent or less) of pine needles as part of the ‘brown’ organic matter in your compost bin. It may take up to a year of more before pine needles decompose using a cold composting method.
Using Pine Needles as Mulch
Another way to use pine needles in the garden is as mulch. Mulch keeps moisture in the soil, reduces weeds, keeps paths mud-free, and controls the soil’s temperature. Also, as the pine needle mulch slowly breaks down, it adds nutrients to the soil, just like adding compost.
Another advantage of pine needle mulch is that it tends to stay put and not get washed away in the rain or when you water your plants. Pine needle mulch also lasts a long time, so you won’t need to replace it often.
You can put down a layer of pine needles up to 3 inches thick when you use them as mulch on garden paths. Brown, dried-out pine needles work best for mulching because they compact easily, creating a firm pathway for walking.
If your source of pine needles is from a pine tree in your garden, another way of dealing with them is to leave them under the pine tree. Sitting where they fall, they provide a natural mulch that feeds the pine tree and keeps weeds away.
The needles at the bottom of the layer slowly rot, releasing nutrients for the tree, and the fresh needles on top look nice and keep the ground from getting muddy when it rains. However, if you live in an area with wildfires, raking up pine needles under a pine tree is a good idea for safety reasons.
Soil Acidity and Composting Pine Needles
The idea that composting pine needles will make your soil acidic probably comes from the fact that green pine needles have a pH of approximately 3.5. This range is relatively acidic for growing plants. However, unless you are mixing lots of green pine needles directly into your soil (a bad idea), the pH level of pine needles quickly moves toward a neutral 6 to 7 range as soon as they start to turn brown and rot.
By the time pine needles become compost, they lose almost all of their acidity.
People might think pine needles make soil acidic because the soil where pine trees grow often has an acid pH. But scientists who study pine trees in nature believe the relationship is the other way around: Pine trees thrive in existing acidic soils. They don’t make the ground become acidic.
If your gardening soil is too alkaline with a pH above 7, you might be looking for ways to lower it to the 6 to 7 range, which is optimum for most garden vegetables and fruit trees. If so, adding pine needles directly to the soil is usually not the way to go.
Instead, start with a soil pH test to determine just how much you need to lower the pH. Then use sulfur or aluminum sulfate fertilizer in recommended quantities to bring down your soil’s pH level.
Some plants prefer slightly acidic soil, and you can take advantage of the somewhat acidic properties of pine needles to make a special compost or mulch for these plants. Acid loving plants include azalea, rhododendron, and camellias.
Using dry or fresh pine needles under these plants can slightly lower the soil’s pH level. Some gardeners also let pine needles rot in a separate pile and then use them to mulch under these so-called ‘lime-hating’ plants.
How to Compost Pine Cones
Pine cones take even longer to decompose than pine needles, but you can still add them to hot or cold compost piles in small amounts. For faster results, chop them up into small pieces with a shovel, put them through a shredder, or crush them with the tires of a lawn tractor before adding them to your compost pile.
You can also use small pine cones as mulch in pathways or under ‘lime-hating’ plants like azaleas. However, pine cones and pine needles are flammable due to their high resin content. Please do not use them as mulch anywhere near your bar-be-cue, fire pit, or where there are open flames from any source.