Gardeners all over the internet seem to agree that dead pine and spruce needles have a high acidity and therefore will acidify any soil where they are used as mulch or dug-into the soil to decay and feed the soil for the following year.
But the truth is, while live needles on the tree are in fact acidic and while the fallen, dead needles are somewhat acidic, they decay so slowly that they do not alter soil pH at all or so little that it really doesn’t make any difference. And here’s how I know…
I know this because I have been using pine needles as a mulch (aka pine mulch or pine straw) in my raised beds for several years now and my soil pH never changes from year to year when I get my soil tests done. I have an abundance of pine needles on my property but I didn’t want to pay for mulch to cover my beds so I decided one year to throw caution to the wind and just use the pine needles as my mulch.
The idea that pine needles cause soil to acidify is an “old wives tale”. It came from farmers who used pine needle mulch in their chicken coops. They used pine needles as bedding because the pine needles soak up acidity in the chickens’ urine. So, at some point, these folks probably tried to use these chicken coop needles as a mulch or fertilizer in their gardens/farms and had no success since the needles were, in fact, acidic since they adsorb the acidity from the chicken waste. So from then on, it was widely believed (apparently to this day) that is was the pine needles themselves (even if not used in as chicken coop bedding) that were to blame for the poor crop, when in fact it was the acid the needles had absorbed from the chicken’s urine, not the needles themselves. This falsity was then probably attributed to all needles of all conifers – to play it safe, I suppose. But who could blame them, they had limited knowledge of these things and their lives depended on their ability to hunt and grow food.
But it’s amazing how we humans will perpetuate a myth or a lie for so long without even seeking the truth through simple, minor experimentation. This makes one wonder how we have gotten as far as we have and how far we could be by now if we weren’t so naive, fearful and gullible as a people, as a race.
But don’t take my word for it, if you have free access to dead pine needle mulch but you’re worried about them making your soil too acidic to grow crops in, mulch a small section of your garden or other part of your property with it for a few years, grow some crops in the soil beneath it and get routine soil tests every year. If you find the acidity tale to be bunk (and I’m sure you will), now you have a nice, free source of great mulch to use on your garden beds. You’re welcome! 🙂
Below you’ll find a couple of sources and a video about this subject of pine needles and soil acidity…