There’s a long-standing debate over whether or not pine needles also known as pine straw or pine mulch is too acidic to use in your garden beds. I have heard both sides of this debate from very knowledgeable people.
PH is a term that is used to measure a substances acidity or alkalinity based on a range scale of 0 to 14. The middle of that scale, number seven, is known as neutral. Any number less than seven is defined as being acidic. Any number above seven is considered alkaline. Most drinking water is around seven or neutral pH. Rainwater is often considered being pure but rainwater actually has a normal pH between 5.5 and six which is slightly acidic.
Green pine needles are slightly acidic but quickly lose their acidity over a short period of time. Once the needles dry and are exposed to the rain they become much more neutral. Soils can buffer the slight acidity of pine needles and negates the slight acidity that pine needles may incur.
It seems that the big disagreement is really on the side of “highly” acidic conditions coming from pine needles. Soil pH is very important to good plant health. A good pH in your soil directly impacts your plants ability to intake nutrients that are in the soil. These nutrients are required for your plants to grow properly. The ideal soil acidity is about between 5.8 and 6.5.
We can come to the agreement that moderate amounts of pine straw mixed in with your compost is not a problem. By the time the pine straw turns from green to brown any problems that could have been caused from acidity or null and void.
The benefits of pine straw far outweigh the negatives. Dry pine straw actually helps provide the proper level of acidity for your plants to thrive and absorb the maximum amount of nutrients from the soil that they can. Pine straw adds an organic compound and nutrients to soil and reduces weeds. When moderate amounts of dry pine straw or added to a compost it is beneficial. Pine straw is like other organic materials found in most compost. Most create some slight acidic conditions.
Pine straw takes a while to break down in a compost pile because it is covered with a waxy substance. Breaking up pine needles in the compost would help them with breaking down. They also are composed of a higher level of carbon like most other fallen leaves. As with other high carbon components added to compost, adding a high nitrogen value will counter this problem. A great compost additive to counter this high carbon that is also found in sawdust would be chicken manure.
The high nitrogen value of chicken manure helps break down the extra carbon that is found in fallen leaves and sawdust. Normally this high carbon value takes nitrogen from the soil that could be used for your plants, so adding more nitrogen to the mixture will aid greatly in your compost.
As a top mulch pine straw is very easy to handle. Pine straw does not tend to float away or wash away. It tends to break down slowly as a mulch topping and does not need to be re-applied frequently. The same pine straw as an additive to a compost pile will also greatly benefit your plants growth and development.