Pine Needle Acidity: Myth or reality?
assured him that pine needles are not a problem as far as acidifying the soil is concerned. When he persisted, I changed the subject. I knew from past experience that this gardening myth was so deeply ingrained in garden lore that with some gardeners there was nothing I could say that would cause them to change their minds.
I do hope, however, to convince the majority of my readers that this is indeed a myth and to offer a few tips along the way for using mulch and, in particular, "pine straw," the usual term for pine needles used as mulch.
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.
Here are some other facts to consider:
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.
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.
nd the larger question: Why mulch at all?
Other reasons to mulch:
*See recent article by DG writer, Sharon Brown
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© Larry Rettig 2009Editor's Note: This article was originally published on November 4, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)