Phoenix Tropicals Gardening

[phoenixtropicals]

It seems there is all kinds of conflicting information on the web about whether pine needles make good mulch or not. One camp says that pine needles are allelopathic (produce chemicals that kill other plants) and another group says that it makes great mulch. The allelopathic group says that the needles produce acids as they decompose that kill other plants.

So, since we live in a place were the soil is very alkaline, I have long had the theory that acid from pine needles is a good thing. For over 5 years I have had a number of trees growing near the drip line of a large Afghan Pine. This pine is very similar looking to a ponderosa, but of course adapted to heat and alkaline soil.

I happily let the pine tree lay down a nice blanket of needles around my other trees. However, over the years I have noticed plants suffering in these locations, especially in the Fall which happens to be a time of year with a lot of pine needle drop. I would expect plants to normally do better in the Fall, not worse because the heat is easing up. Part of my rye grass lawn is also under this tree, but suffers no ill affects. Then again the lawn mower always sweeps up the pine needles there.

This leads me to another theory I have seen on the internet. The theory is that the needles themselves are not really a problem, rather the pine roots are so competitive and the shade cast by the tree is such that other plants don't grow. However, my lawn doing just fine under the tree seems to shoot down that theory.

Therefore, I have only one conclusion that makes sense. Those darn needles are hard on other plants, and it must be more than just some kind of acidification of the soil, because that wouldn't be a problem here in Phoenix.

So, today I did some serious raking around the plants near my pine tree, and pulled up all the needles I could reasonably collect. It will be interesting to see the result.

I also did this years ago below a eucalyptus with positive results. By the way, that pine tree produces some great afternoon shade for some of my fruit trees, so I don't want to get rid of it completely.

[phoenixtropicals]

Here's an interesting article. Looks like "phenolics" are produced by pine needles. I also imagine that maybe full composting would destroy these negative chemicals and this is why many people find pine needles good for compost.

http://www.sustland.umn.edu/implement/trees_turf.html