Do Pine Trees Cause Acidic Soil?

Pines are part of the Pinaceae family of evergreen, coniferous, and resinous trees. Their needles remain on the tree for several years before falling off. These fallen needles are a concern for many because of their acidity levels. One common question people ask is whether pine trees cause acidic soil.

The quick and easy answer is, “No.” While fallen pine needles are a bit acidic, the belief that they’re capable of affecting the acidity of the soil is a myth that has been floating around for years.

Related Post: Do Pine Trees Die In The Winter Or Harsh Conditions?

Pine Trees and Acidic Soil

Let’s start with the pH levels in general before moving on to pine needles, or pine straws as they’re sometimes called.

Soil pH Levels

Any type of soil has a particular pH level. The pH scale ranges in value from 1 (strongly acidic) to 14 (strongly alkaline).

The middle point on the pH scale is between 6.5 and 7.0. This is a neutral pH, which means it’s neither acidic nor alkaline. This type of soil is the most suitable type for all kinds of plant species.

Pine pH Levels

While healthy and living on the tree, pine needles have a pH level that ranges between 6.0 and 6.5. This is in the range of neutral and slightly acidic, which is a healthy level that suits almost all kinds of plants.

The controversy starts when pine needles fall off the branches. Once on the ground, their pH levels drop to levels that range between 3.2 and 3.8. This is definitely more acidic than before.

What does this mean for the soil? This drop in the needles’ pH levels may lead to a temporary shift in the acidity of the soil. However, this shift is so meager that it’s almost insignificant.

Researchers weren’t able to record any significant changes in the soil’s pH levels. So they consider it to be nonexistent.

This is good news for the soil, but what about the surrounding plants? The good news is that these highly acidic fallen pine needles don’t harm the nearby plants in any way.

Why Is It Hard for Plants to Grow Under Pine Trees?

Found mainly in the Northern Hemisphere, pine trees have long been seen as a sign of endurance, adaptability, and wisdom. Yet, many find it difficult to grow other plants underneath pine trees.

Dirt road in pine wood
Yay Dirt road in pine wood

This is a common concern among gardeners and farmers. While this may pose a real problem for many, the cause has nothing to do with the acidity levels of the fallen pine needles.

There are two main reasons why plants find it hard to grow under pines. 

Shade Under the Tree

One obvious reason for certain plants not being able to grow a pine tree is because of shade. The majority of pine trees can grow anywhere from 50 to 150 feet high. Some can even reach up to 260 feet tall.

This creates a big area of shade underneath where sunlight can’t get through. If there’s not enough sunlight to reach the plants, then they won’t be able to make food.

If they can’t make food, they can’t survive. It’s that simple.

Pine Tree Roots

The second reason why it may be hard to grow plants under a pine tree has to do with the sheer volume of roots. Evergreens are known for having countless roots that are close to the surface.

These roots battle for water and nutrients when a different plant species show up. Because they’re so shallow and there are so many of them, they usually win the fight. As a result, other plants don’t make it and quickly wither away.

Advantages of Using Pine Needles as Mulch

Pine needles become more acidic once they fall off the tree. Yet, they don’t have the power to affect the pH level of the soil.

Furthermore, they become neutral once they begin decomposing. The reason? Decomposers in the soil somehow manage to neutralize their acidity as they break them down.

Fallen pine needles and leaves
Yay Fallen pine needles and leaves

This is one reason why pine needles make such good mulch. One option is to leave them right where they fall under their tree.

Another option is to spread them around in vegetable gardens and the edges of flowerbeds. Here are some more benefits to using pine needles to boost the health of the soil and plants.

  • Don’t cost anything
  • Are easy to obtain
  • Manage to suppress weeds
  • Add nutrients to the soil, such as calcium, potassium, and magnesium
  • Stay loose without creating an impervious covering as other types of mulches
  • Remain stable, even during heavy rains
  • Last longer when compared with other types of mulches
  • Retain soil moisture
  • Keep termites and other bugs away