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The purpose of ericaceous compost is to modify the soil pH to create a more acidic growing environment for acid-loving ericaceous plants. Pine needles are known to be acidic, so can they be used to make your own ericaceous compost?
Pine needles do not make ericaceous compost. Pine needles lose their acidity over a period of 3 weeks, making them ineffective at producing an acidic compost. The pine needles’ structure and acidity make them decompose slower than other organic materials in the compost pile.
Pine needles are an abundant organic resource available in a wide range of climates. Pine trees drop enormous amounts of needles throughout the season, creating a blanket of pine needles beneath the trees. Are these pine needles acidic enough to include in your compost pile to create ericaceous compost, or what other methods can you use to make use of pine needle acidity?
Can You Make Ericaceous Compost With Pine Needles?
If you have pine trees growing in your garden or your neighborhood, you will know what I am talking about when I call the pine needles beneath the tree a blanket.
This may seem unusual since pine trees are evergreen, but evergreen does not mean the pine needles stay on the tree indefinitely. The needles fall off the tree periodically and are replaced by new growth.
Not much grows beneath pine trees when a blanket of needles covers the ground around the tree’s base. Is this due to the acidity of the pine needles, or the pine needles acting as a thick mulch layer, preventing the growth of other plants under the tree?
There is no disputing that pine needles are acidic, with a pH of between 3.2 and 3.8 and an average of about 3.5. However, when you add pine needles to your compost, the resulting compost is no more acidic than any other compost.
This means that pine needles do not make ericaceous compost and will not provide the acidic environment needed for your ericaceous plants.
Why Don’t Pine Needles Make Ericaceous Compost?
Pine needles are acidic when they are green and when they have recently fallen from the pine tree. The acidity in the pine needles rapidly breaks down and neutralizes as the pine needles age and dry out.
The time it takes for the acidity to reduce to an almost neutral pH in the needles is about 3 weeks. Since pine needles take much longer than this to break down in compost, they are no longer acidic when the compost is ready to be used.
Pine needles are coated in a waxy substance that is part of their protection against water loss, but this waxy layer takes a long time to break down in a compost pile.
The initial low pH of the pine needles slows down the composting process in the compost pile since most of the organisms and microbes do not flourish in an acidic environment.
The duration for pine needles to break down goes far beyond when they remain acidic. This results in a pine needle compost with the same pH values as normal compost.
Can You Speed Up Pine Needle Composting For Ericaceous Compost?
Pine needles make an excellent compost material, adding good levels of carbon to the resulting compost. Can you speed up the composting process for pine needles and, in this way, have a lower pH compost?
There are ways to speed up the rate of decomposition of pine needles, which mostly means increasing the surface area of the needles available for the composting microbes to work on.
The best way to speed up the decomposition of pine needles in your compost is to chop the needles into smaller pieces. This can be achieved by running a lawnmower over the pine needles a few times or by feeding the pine needles through a garden chipper.
While this process will make the pine needles decompose faster, it is still not fast enough for any of the remaining acidity to have any effect on the overall pH of the finished compost.
Can Pine Needles Be Used To Amend Soil pH?
There is still a way to use pine needles to benefit your ericaceous plants, albeit temporarily. The key is to use the pine needles while they are at their most acidic.
Digging chopped-up fresh, green pine needles or freshly fallen pine needles into the soil directly around your ericaceous plants is the best way to benefit from the acidity in the needles. Don’t compost the needles; dig them into the soil directly.
It is likely that the pine needles alone will not be sufficient to reduce the soil pH, so you will need other methods, such as coffee grounds, to supplement the pine needles to get the soil pH to the desired range.
The higher acidity of the fresh needles will help with other pH amendment methods to temporarily amend the soil to a lower pH, which your acid-loving plants will enjoy.
The amendment is temporary because the needles will lose their acidity over about 3 weeks, after which they will no longer affect the soil pH.
You can counter this by digging fresh pine needles into the soil every three weeks or so to maintain the lower pH value, but this can become a tiresome chore, in my experience.
Can You Make Your Own Ericaceous Compost?
You can make your own ericaceous compost by creating normal compost first and then amending the pH of the compost to the right level before adding it to the soil for your acid-loving plants.
When the composting process is well underway, add coffee grounds, leaf mold made from oak or maple leaves, and sawdust, preferably from conifer trees.
Do not add manure or lime to your compost, as this will have the opposite effect and make the compost alkaline.
Keep testing the compost with your pH meter to make sure the correct pH of 5.0 to 5.5 is attained. You can also add organic soil sulfur to the compost. Organic soil sulfur is available from most garden centers or nurseries.
Do not use any sulfates to lower the soil pH, such as aluminum sulfate. These substances have too much salt and will make your soil too salty for your plants to thrive.
Final Thoughts
Pine needles are acidic, but the acid levels in the needles rapidly diminish once the needles have fallen from the tree. This makes pine needles suitable for composting, but it does not make the compost acidic.
The pine needles are no longer acidic once the composting process has been completed and will not lower the pH of the compost to create an ericaceous compost.
Sources
- https://www.ag.ndsu.edu/horticulture/joes-old-pages/normal-fall-needle-drop-in-conifers
- https://extension.unh.edu/blog/2019/10/do-pine-trees-pine-needles-make-soil-more-acidic
- https://www.wnps.org/blog/ponderosa-pine-needles-composting
